Flange distance and back focus?

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Mark Davies

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Flange distance and back focus?

PostSat May 03, 2014 8:54 am

I just tested my Canon CN-E Primes and the lens witness marks do not match up and so the backfocus on my BM4K is out. How can I adjust back focus on the BM4K? Or can this be put right? One of the reasons I bought the CN-E lenses was so I could properly focus with a tape measure in a professional way with the BM4K.
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Dustin Boswell

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Re: Flange distance and back focus?

PostSat May 03, 2014 9:13 am

are you measuring from the sensor or from the lens?
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Mark Davies

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Re: Flange distance and back focus?

PostSat May 03, 2014 11:30 am

From the sensor
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Mark Davies

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Re: Flange distance and back focus?

PostSat May 03, 2014 11:35 am

Found a fix A couple of bits of tape Top and bottom gets it about right.
I've now seen some other posts and it appears BM made the flange distance correct for the BMCC then did a recall and changed it to suit the Tokina and to allow for lenses that were out. Unbelievable.. I suppose that thinking has transferred to the 4K camera. So take a standard and throw it out in order to make lenses built to the wrong tolerances work.

BM Please could you make available as an accessory A new flange lip so those with proper lenses can use them?
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adamroberts

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Re: Flange distance and back focus?

PostSat May 03, 2014 2:02 pm

The EF mount is not a Cine mount. It was designed for a stills camera where the tolerances not as tight.

As a result it has to have some tolerance built in for lens mount differences as there is no way to shim an EF mount like you can a PL mount.
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Mark Davies

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Re: Flange distance and back focus?

PostSat May 03, 2014 2:16 pm

Why cant BM make a slightly thicker flange plate as an accessory so we can put a new one on that is made for lenses that are not out.
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adamroberts

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Re: Flange distance and back focus?

PostSat May 03, 2014 2:37 pm

Try those lenses on 3 different Canon bodies. All of them will be different. It's not a BM issue. It's just how the EF mount is.

You could always shim the lenses.
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Mark Davies

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Re: Flange distance and back focus?

PostSat May 03, 2014 4:09 pm

Adam,

No its how BM's EF mount is and while manufacturers may play to lower quality lens makers The truth is there is nothing wrong with the EF mount Only how it is implemented.
Everyone of My CN-E lenses will have accurate witness marks It is the fault of BM for allowing a huge margin of error for lenses like the tokina.
Lets put the blame where it lies and bring this to the attention of BM Because if they wish to sell these cameras as professional then accurate witness marks on accurate lenses should be the norm Otherwise the word professional makes no sense.
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rick.lang

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Re: Flange distance and back focus?

PostSat May 03, 2014 9:12 pm

adamroberts wrote:The EF mount is not a Cine mount. It was designed for a stills camera where the tolerances not as tight.

As a result it has to have some tolerance built in for lens mount differences as there is no way to shim an EF mount like you can a PL mount.


Adam, I think this is not correct to imply the BMPC4K and certainly the URSA cameras are designed with the expectation that stills lenses only will be used . When you look at the CN-E primes and zooms, these are not inexpensive lenses and Canon does make them to fit either EF or PL mounts. Your point is well taken about the original BMCC EF. Although these very expensive EF lenses could be used on a Canon EOS Rebel XT, realistically, a zoom lens that costs 5 figures is not likely to be used on the Rebel. When someone buys the BMPC4K or URSA EF especially, they'll expect the best quality EF lenses to work properly.

Would be appreciated very much if BMD would let us know if the flange distance is identical on the BMCC EF, the BMPC4K, and the URSA EF. If it is, they may not sell as many EF mount 4K cameras. Given the high quality of Canon's 4K cinema lenses, certainly BMD 4K cameras should work well with the witness marks. But you may be correct of course that there may be a majority of users putting stills glass on the 4K cameras and BMD choose to accommodate those users' lenses at the expense of ciné lenses. We just deserve to be aware. If you are correct, they will sell more URSA PL cameras (since we know Tokina 11-16mm zooms are not likely to be used there) and the flange distance will be on spec.

BMD please respond shortly rather than let early adopters of the URSA find out the hard way.

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Tom

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Re: Flange distance and back focus?

PostSun May 04, 2014 12:14 am

Just out of curiosity, have you checked in a dslr with ef mount as to how accurate those lens markings are - i suspect you will find them also innacurate.
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rick.lang

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Re: Flange distance and back focus?

PostSun May 04, 2014 2:51 am

Excellent suggestion, Tom. I was assuming the CN-E primes would be good, but best to test on a good EOS camera.


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adamroberts

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Re: Flange distance and back focus?

PostSun May 04, 2014 6:54 am

Which is exactly what I said. The EF mount is not as precise as a PL mount. Never will be as you can't shim the mount.
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Mark Davies

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Re: Flange distance and back focus?

PostSun May 04, 2014 7:02 am

Tom,

The CN-E lenses are £3500 a pop So come on What are you paying for if these lenses are innacurate. This is not some cut price bargain from india.

If you read my earlier post I mentioned that I've put some tape on the EF MOUNT This tape is very thin and after two layers my witness marks now match up. Of course this is not as accurate as a properly built mount The BM4K Mount IS TO SHORT. They did this so that lenses like the tokina would still be able to focus at infinity and that is why my 24mm at 5' is 6" short at infinity it focuses at about 15 to 20' In closeup it wont focus at all.

However as I said I put some tape on the mount.

Rick
Why do you think BM should give distances for the URSA? shouldn't THIS also be the case for the BM4K and all the cameras?
ALL PRO lens witness marks on BM cameras are going to be OUT. That was the reason I went for the BM4K EF and that reason and my spending money I don't have on CN-E lenses was pointless But this is just another notch in BM's refusal to not be straight up and mis advertise their cameras. While I understand they are new to making cameras the refusal to put right or help is just very annoying.

BM Make a slightly thicker flange plate as an accessory so we can buy it for pro lens witness mark accuracy.

Or stop calling these cameras professional.
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Mark Davies

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Re: Flange distance and back focus?

PostSun May 04, 2014 7:12 am

adamroberts wrote:Which is exactly what I said. The EF mount is not as precise as a PL mount. Never will be as you can't shim the mount.

So why not just make a thicker flange plate as an accessory?
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adamroberts

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Re: Flange distance and back focus?

PostSun May 04, 2014 8:47 am

How much thicker?

When you shim a PL mount (which you need to do from time to time because metal wears) you use shims that are just a few microns thick. Often thinner than paper.

It takes just 0.001mm for your focus marks to be out.

Just because a lens is £3600 does not mean the mount it accurate. The CN-E lenses can also be shimmed as they too will wear over time and become in accurate.

Like I said before, and at Tom has said, test those lenses on other EF mounts and you'll see the results will differ on all of them.
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Mark Davies

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Re: Flange distance and back focus?

PostSun May 04, 2014 9:12 am

Adam

This is all getting a little weird.

BM have made the EF mount to short in order to make allowances for lenses that are out. What part of that is not registering?

If you know that then you can logically understand why this throws out the witness marks on pro lenses.

All this test CN-E lenses on another camera as they are likely to be out is a bit of a troll isn't it?
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Tom

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Re: Flange distance and back focus?

PostSun May 04, 2014 10:21 am

I think we all know and understand about the blackmagic mount, the point we are making is in regards to the general accuracy of the mount system, rather than this being a problem with a specific camera. Which is why we keep suggesting you at least try the lens on another EF mount camera.
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Alastair Traill

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Re: Flange distance and back focus?

PostSun May 04, 2014 10:38 am

Hi Mark,

I spent a bit of time today adjusting the length of a Nikon G – MFT adapter to make my combination of BMPCC / Sigma 18-35 and adapter the correct dimensions to obtain parfocality and align infinity mark. The account is on this forum under the heading ‘Lens Flange distance for BMPCC’, it may be of interest.
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adamroberts

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Re: Flange distance and back focus?

PostSun May 04, 2014 11:03 am

Tom wrote:I think we all know and understand about the blackmagic mount, the point we are making is in regards to the general accuracy of the mount system, rather than this being a problem with a specific camera. Which is why we keep suggesting you at least try the lens on another EF mount camera.

What he said.

Try those lenses on a 5D, C100, C300, 1DC.... all of them will be different.

The EF mount, on any camera, is not precise enough for true cine lenses. Fact.

The only way you will get a mount precise is to shim it. EF mount does not offer that ability. Even if the mount was spot on when it left the factory the mount will wear over time and be out within months. This is why a PL mount is shimable and has to constantly be checked and adjusted.
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Mark Davies

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Re: Flange distance and back focus?

PostSun May 04, 2014 11:57 am

Hi Alistair
Yes I did read your thread I've also found a workaround by putting two layers of very thin tape on my mount which seems to get the witness marks on the 24mm lens (Which is the worst out) lined up correctly. This is now workable with a tape measure However it will never be exact and I don't have the tools you do. What would be best is if BM acknowledge this by making available a new flange plate that has the exact measurements for an EF mount.

TOM
I think we all know and understand about the blackmagic mount, the point we are making is in regards to the general accuracy of the mount system, rather than this being a problem with a specific camera. Which is why we keep suggesting you at least try the lens on another EF mount camera.


Why didn't you say this in the beginning. So you understand the BM mount is innacurate and why the witness marks will be out on any professional lens and yet you insist I should test my lenses on another camera. Presumably to make the point all EF lens Mounts are out and to back up Adams statement this is the case. But you are not going to mention the fact BM did a recall on their BMCC cameras because the flange was set for CN-E lenses and other lenses like Tokina couldn't focus to affinity are you. No you want me to waste my time to make you and your friend look good?

ADAM
Okay as you are being obstructive I will try a different way.
Your argument seems to be dissatisfaction with the fact an EF mount is not shimmable and decided this is the place to air that grievance so you want my thread to promote your cause (Why not start your own thread?) and I want to argue for BM to make a thicker flange plate that is accurate and caters to pro tolerances so pro crews can use a tape measure instead of the one fitted that allows a huge margin of error that allows those lens manufacturers making inaccurate mounts for their lenses to reach infinity.

BM could please both. With a new flange plate accessory that is accurate.

Your argument the EF mount is not shimmable and all lenses are out is exasperating the problem instead of trying to help solve it.
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adamroberts

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Re: Flange distance and back focus?

PostSun May 04, 2014 4:36 pm

I have no issue with the EF mount. It's a stills camera mount. It will NEVER be accurate. EVER. It not part of its design.

You say the "24mm lens (Which is the worst out)" so you mean they are not all out by the same margin??? That says to me the lenses are also out. Have you had the lenses checked on a collimator to see if they are all correctly shimmed??

To get perfectly accurate witness marks you need to have the mount checked with a collimator then shimmed if necessary and checked again. You probably can have that done on the EF mount if you take the camera to a cine lens & camera service centre or rental house that has a collimator. Probably can place custom shims behind the mount.

Your lenses then also need to be check with a collimator and shimmed if need.

Only then will they be accurate.

I have some PL mount lenses that are correct. My BMCC was fine with my Tokina. Maybe a touch soft. All my other Canon EF lenses focused passed infinity. When I got my PL adaptor all of my PL lenses would not reach infinity. They maybe reached 5m. On the BMPC4K they focused correctly. BM then replaced my BMCC. Now my PL mount lenses reach infinity with my PL adaptor.

Even Canon EF lenses are built with loose tolerances because Canon know the EF mount is not 100% spot on.

Even if BM sent you a mount that was 100% spot on, it would be out in a few months due to wear from changing lenses.
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Mark Davies

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Re: Flange distance and back focus?

PostSun May 04, 2014 5:37 pm

No they are ALL NOW accurate because as I have said twice before I have put two layers of thin tape on the flange plate.
The EF mount spec is supposed to be 44mm not 42mm and that is the problem and why my lens witness marks are out. What you are saying is I should take a professional standard and change it to fit with a wrongly made EF mount on the BM.
It is the mount that is out. While tape is a temporary fix I'd rather have a more permanent solution in the form of a new thicker flange plate from BM that is accurate.
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rick.lang

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Re: Flange distance and back focus?

PostSun May 04, 2014 6:36 pm

Mark, my previous post was intended to be supportive of your position so don't know why you seemed to be unhappy with what I said.

The modified BMCC is a horse out of the barn and not likely to be reverted back to the original specs. I was hoping both the BMPC4K and the URSA would be using the original specs, not the mod added to the BMCC cameras. Since you mentioned you had a problem with the BMPC4K, I suspect they have applied the BMCC mod to it as well. But the URSA isn't yet running off a production line and, you must admit, it appears to be designed with a strong nod to professional users' requirements, even though all their cameras are being used by professionals. So I'd expect all the 4K cameras to have the correct EF flange to begin with. I did say that, but I want to hear from BMD.

"When someone buys the BMPC4K or URSA EF especially, they'll expect the best quality EF lenses to work properly.

Would be appreciated very much if BMD would let us know if the flange distance is identical on the BMCC EF, the BMPC4K, and the URSA EF."

If the EF flange is not precise, then I also mentioned that they will sell more URSA PL cameras (because some people expect PL will have a precise flange spec). I can accept that wear and tear exists on a used camera, but at least start with an accurate flange.

If I recall correctly at the time of the BMCC EF flange change, someone stated that the BMCC MFT camera didn't require the same flange change because BMD belonged to the MFT consortium and would have access to published specs and be expected to adhere to those specs as a member. Even though an EF mount might make the most sense for me, I'm feeling more inclined to the MFT and PL mount

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adamroberts

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Re: Flange distance and back focus?

PostSun May 04, 2014 6:41 pm

Mark2929 wrote:I have put two layers of thin tape on the flange plate

Mark2929 wrote:EF mount spec is supposed to be 44mm not 42mm and that is the problem

2 layers of thin tape is not gonna give you 2mm. In fact if your mount was 2mm out there is no way you could place 2mm of tape between your mount and the lens. The lens would simply not mount.

As I've said before, try those lenses on other EF mounts and you will find they are also not 100% accurate. That is just the nature of the EF mount.

I'm not saying your BMPC4K mount is correct, because it's not. I'm saying that no EF mount is. They are all mass produced and there is no way to get mass produced mounts to be accurate to within 0.001mm.
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Mark Davies

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Re: Flange distance and back focus?

PostSun May 04, 2014 8:08 pm

Okay Rick, I hope BM will inform you what size the mount is. Though for me its not going to make any difference,

Adam,
I don't know what BM size the 4kBM mount is But I know they designed it to take into account all lenses and therefore will NOT be accurate for my CN-E lens witness marks. The reason I can say this with almost certainty is because no one with a tokina like lens has said their focus wont go to infinity.

The 4K mount is out That is A FACT. Something though we can both agree on.

BLACK MAGIC IF YOU'RE LISTENING
We need clarification on the size of the mount as it aint 44mm
We need a flange plate that takes the mount up to a true 44mm That can be bought separately please.


I also think this would be very innovative and a solution to the EF Mount not being shimmable in the traditional way!
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Tom

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Re: Flange distance and back focus?

PostSun May 04, 2014 8:30 pm

Mark2929 wrote:I also think this would be very innovative and a solution to the EF Mount not being shimmable in the traditional way!




You might want to speak to Canon seeing as it is their mount, their lenses and their spec. You know why the top end cameras use PL mount, and why Canon also supply their own cine lenses in another mount other than EF - because EF is not suitable for the accuracy required with those lenses.

I am sure if you contacted BMD and asked them to modify your mount, they would perhaps give you advice on how to go about getting that done. But getting so defensive about us pointing out the flaws of the EF mount system is not going to resolve your problem. The problem you are experiencing is not unique to blackmagic cameras, it exists on all EF mount systems.

The reason a PL mount is so expensive even though it is a passive "dumb" mount, is precisely because it allows one to have such issues resolved. You are talking about adjustments made in Microns, not mm. The tolerances required are so extreme that there is no way it would be feasible on such a loose mounting system as EF.

I am not trying to upset you or "troll" you, I am trying to explain in detail why what you seek is just not possible with the mounting system you want to use.
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Re: Flange distance and back focus?

PostSun May 04, 2014 9:47 pm

Tom
Two layer of tape got my BMCC within the ballpark I would say focusing is still a smiff short but not that it makes any difference worth talking about.

Do you actually know anything about this? Seriously I don't think you do.
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John Brawley

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Re: Flange distance and back focus?

PostSun May 04, 2014 10:07 pm

Mark.

No cinema lens collimates perfectly on every camera.

It's a standard part of the prep process. I speak from experience. I spent three years at a rental company where we would DAILY re-shim and re-collimate both lenses and camera bodies.

Sometimes the camera needs to be shimmed. Sometimes it's the lens. Sometimes it's both. You can overlap one being out with the other, but ideally the camera is shimmed to a known depth, the FFD, and then the lens is shimmed to project an image in focus at the same FFD.

I bought brand new Zeiss CP2's and 3 of the 6 lenses had to be re-shimmed because they didn't even pass the QA of the lens tech at the local re-seller where I bought them.

You can't assume lenses are correct just because they've come from Canon. Have you had them checked by a tech on a lens collimator ?

When someone asks you to check the lenses on another body, it's a standard way of checking if it's the lenses or the bodies. In the absence of a lens collimator, which I assume you don't have, it's the next best thing.

A lens can be OUT but still hit the right witness marks on a body that's also out.

Putting your specific issue aside for a second, the EF lens mount is highly problematic.

The reason it's so problematic is that it's a 20 year old STILLS mount that's been adapted to motion imaging. The legacy of that mount is that of the reputed 100 million EF mount lenses that have been made, the very vast majority of them are going on stills cameras that AF.

That means they need to be mass produced and cheap. The focusing groups inside the lens need to be really light so the AF motors can drive them quickly. This means you get a lot of play and inconsistency in focussing setup to setup but no-one ever notices because they never actually use the witness marks on the lens, the witness marks are never accurate enough to be used either. Even if you MF the lens you're still using your eyes, so again, you'd never notice if it didn't hit the same witness mark.

Now because of this sloppiness in the mass produced EF lenses, they build in some overhead by doing two things. They shorten their own EF mount standard on their bodies and they make lenses that focus past infinity.

This allows Canon to make lenses less expensively with less precision.

Now, look at it from BM's perspective.

They started off by making a camera that was EXACTLY the standard you're now demanding. And there was a huge ruckus because the very vast majority of users are using stills lenses. Not CN-E lenses. So their lenses now suddenly won't always hit infinity.

You're in a huge minority Mark because you use a lens that evry few others do. I'm willing to bet you're a 1 in 1000 user. So should they screw the other 999 users just so you can have witness marks for your EF mount ?

I think you can understand why they decided to do WHAT CANON THEMSELVES DO and make their EF mount's short.

Now, you can't shim the EF mount. But, you can re-shim your lenses.

The really easy solution for you if you like your CN-E lenses is to collimate them to your camera. Like we've always done in filmmaking for decades. Go to any decent rental company and ask them to shim your lenses to your camera. Then your focus marks will line up. Problem solved.

Your use of a bit of tape is a really bad idea. Mainly because it will change over time as you compress it and as it attracts dirt.

Your suggestion of a flange adaptor plate is unworkable. Most flange adjustments are really really tiny. Thinner than a piece of aluminium.

Look at this Zeiss document. It details the changes in shims you need to make to correct focus scales.
http://www.zeiss.com/content/dam/Photog ... r_CP.2.pdf

Look at this Zeiss document. They actually have a chapter thats headed "Adjusting your lens to your camera"
http://www.zeiss.com/content/dam/Photog ... ctions.pdf

And this is exactly why I would never purchase or use CN-E lenses in EF mount.

It commits you to a mount that usually can't be shimmed and has other issues with use in motion imaging. For example, you'll find that a heavier cine lens will rotate int he mount when used with a follow focus. There is no way of locking the rotational torque that that follow focus introduces on the lens.

The end result is that you're image will "shift" or "move" as you rack the follow focus hard.

There's nothing you can do about that. That's also why Canon themselves with the C500 introduced a lockable EF mount. RED also did something similar with their dual locking ring $2000 titanium EF mount.
http://www.red.com/store/products/dsmc-ti-canon-mount

Both of these mounts attempt to address this well known shortcoming.

PL by the way stands for Positive Lock. It has a locating PIN in the mount that prevents rotational torque.

The fact is, you never see EF mount's on larger sets....they have lot's of issues just like this.

EF isn't a good idea for motion imaging. It's generally not shimmable on the body side and the lens will rotate in the mount when used with a follow focus.

Never say never and of course there will be exceptions, but all things being equal I don't know many that would CHOOSE EF when they could use PL.

This is why when I needed to buy some primes, I went for the Zeiss CP2's. They offer an interchangeable mount that is designed to be changed by the user (not a technician) and they offer EF as well as PL or MFT.

Right now I have a Zeiss CP 50 Macro in EF mount that lives on my 4K and my 2.5K cameras have (shimable) MFT-->PV mount adaptors for the PV mount lenses I have.

I think every post has been so far, trying to help and explore your issue. It does you no favours to respond with vitriol and insulting those that seek to genuinely help you. I'm seeking to do the same.

JB
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Mark Davies

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Re: Flange distance and back focus?

PostSun May 04, 2014 11:14 pm

Thanks John

You've sort of touched on the problem but basically skimmed over it.

BM did make the mount correct in the first place using CN-E lenses as their guide Had this remained the case My lenses would have worked fine. They then overcompensated for the tokina 11-16mm which was out As a result of this no witness marks on pro lenses would ever be right. However that hasn't stopped BM from plastering pictures all over their advertising buff using CN-E lenses and describing the camera for use with the worlds best lens crafters without mentioning the wibbly wobbly EF Mount.

You're right I could get my lenses collimated for BM's wrongly sized EF mount and then recollimated again if I buy another camera in the future. Yes BM got slated for those lenses wrongly made and with infinity issues so lets not mention that Lets blame the idiot who went out and spent all he had on a set of pro lenses That's far better isn't it.

I bought brand new Zeiss CP2's and 3 of the 6 lenses had to be re-shimmed because they didn't even pass the QA of the lens tech at the local re-seller where I bought them.
Yes the CP2's are shimmable with a kit and instructions how to do it So no problem there then.

You can't assume lenses are correct just because they've come from Canon. Have you had them checked by a tech on a lens collimator ?

After testing ALL my CN-E lenses now match with two layers of thin tape.

When someone asks you to check the lenses on another body, it's a standard way of checking if it's the lenses or the bodies. In the absence of a lens collimator, which I assume you don't have, it's the next best thing.

Yes but that would mean ALL my lenses are out by the same degree I would agree with you if one were different But they are all the same now.

A lens can be OUT but still hit the right witness marks on a body that's also out.

Two wrongs make a right?

Putting your specific issue aside for a second, the EF lens mount is highly problematic.

No its not Its only problematic when information is not given Like for example "Buy a BM camera and use the worlds best lens crafters but dont forget we made the mount to cater for the lens most out so your witness marks wont work and you will need to recollimate your lenses so their not accurate to the EF spec.

The reason it's so problematic is that it's a 20 year old STILLS mount that's been adapted to motion imaging. The legacy of that mount is that of the reputed 100 million EF mount lenses that have been made, the very vast majority of them are going on stills cameras that AF.

Yes but BM cited using Canon CN-E lenses and indeed made the EF mount using them as a reference. Only changing it after complaints fromTokina users who also seem to have issues with the canon c300

That means they need to be mass produced and cheap. The focusing groups inside the lens need to be really light so the AF motors can drive them quickly. This means you get a lot of play and inconsistency in focussing setup to setup but no-one ever notices because they never actually use the witness marks on the lens, the witness marks are never accurate enough to be used either. Even if you MF the lens you're still using your eyes, so again, you'd never notice if it didn't hit the same witness mark.

No the reason witness marks cant be used on the EF mount is because the mount is out.

Now because of this sloppiness in the mass produced EF lenses, they build in some overhead by doing two things. They shorten their own EF mount standard on their bodies and they make lenses that focus past infinity.

Initially BM made the mount according to the EF spec.

This allows Canon to make lenses less expensively with less precision.

Not so with their CN-E lineup though.

Now, look at it from BM's perspective.


They started off by making a camera that was EXACTLY the standard you're now demanding. And there was a huge ruckus because the very vast majority of users are using stills lenses. Not CN-E lenses. So their lenses now suddenly won't always hit infinity.

That was the reason they introduced the M4/3 mount Or at least it should have been.

You're in a huge minority Mark because you use a lens that evry few others do. I'm willing to bet you're a 1 in 1000 user. So should they screw the other 999 users just so you can have witness marks for your EF mount ?

No they shouldnt screw other users They should screw me instead. I think where the problem lies is the advertisement guff and the lack of information

I think you can understand why they decided to do WHAT CANON THEMSELVES DO and make their EF mount's short.

Yes I understand they needed to please those buying the cameras and I agree But just not with the way they did it. You see if I had known this I would never have bought the CN-E lenses.

Now, you can't shim the EF mount. But, you can re-shim your lenses.

BM could though get their factory to make a flange plate that is the correct thickness and sell it to us. Although you believe BM's mistake however good intentioned should be my problem.

The really easy solution for you if you like your CN-E lenses is to collimate them to your camera. Like we've always done in filmmaking for decades. Go to any decent rental company and ask them to shim your lenses to your camera. Then your focus marks will line up. Problem solved.

I think it would very helful if BM could make a flange plate of the correct thickness.

Your use of a bit of tape is a really bad idea. Mainly because it will change over time as you compress it and as it attracts dirt.

Well At least you didnt call me a liar! Its a workaround for now. Thanks BM.

Your suggestion of a flange adaptor plate is unworkable. Most flange adjustments are really really tiny. Thinner than a piece of aluminium.

Whatever the thickness and I believe it is far more than a few microns It could easily be done by BM's factory Not a piece of ultra thin metal But a properly sized flange plate to replace the old on Just unscrew it and screw your new one on,

Look at this Zeiss document. It details the changes in shims you need to make to correct focus scales.
http://www.zeiss.com/content/dam/Photog ... r_CP.2.pdf


Look at this Zeiss document. They actually have a chapter thats headed "Adjusting your lens to your camera"
http://www.zeiss.com/content/dam/Photog ... ctions.pdf


And this is exactly why I would never purchase or use CN-E lenses in EF mount.


It commits you to a mount that usually can't be shimmed and has other issues with use in motion imaging. For example, you'll find that a heavier cine lens will rotate int he mount when used with a follow focus. There is no way of locking the rotational torque that that follow focus introduces on the lens.

So you're saying I couldnt get my CN-E's collimated anyway

The end result is that you're image will "shift" or "move" as you rack the follow focus hard.

EF isn't a good idea for motion imaging. It's generally not shimmable on the body side and the lens will rotate in the mount when used with a follow focus.
Really? So why does the lens lock into place on the BM mount?


This is why when I needed to buy some primes, I went for the Zeiss CP2's. They offer an interchangeable mount that is designed to be changed by the user (not a technician) and they offer EF as well as PL or MFT.

I prefer the CN-E's as they are sharper better colour rendition and open wider.

I think every post has been so far, trying to help and explore your issue. It does you no favours to respond with vitriol and insulting those that seek to genuinely help you. I'm seeking to do the same.

No Vitriol coming from me JB Just a request to BM for a new flange plate that works to the correct tolerances so I can use the lenses they advertise the camera for in a professional way

MD


Here's what a rental house said
http://www.mkeproductionrental.com/back ... -ef-mount/
WHY the black magic camera shouldn't be used with zooms
http://wolfcrow.com/blog/why-the-blackm ... ith-zooms/
BM Users forum explaining why BM changed the mount Seems they started of as silly as me and then went on to make a mount for all unprofessional lenses out there and keep the heading about the camera being professional Shame they didn't tell me in the advertising this was the case.

When Blackmagic designed the BMCC, they designed it to match with Canon’s cinema lenses. These lenses are pricey, and made to much more exact measurements than Canon’s photo lenses, even their L series. Most of the high-end lenses with EF mounts have very precise focus marks on the barrel. They stop at exactly infinity. Then, they released it to the public, and realized that certain lenses are really meant to mount much closer to the camera sensor. Oops! Plenty of wide-angle lenses that worked perfectly on cameras like the 5D mark III couldn’t focus to infinity on the BMCC. So they performed a recall, and every lens mount they made afterward was adjusted to allow for the wider tolerance of photo lenses. This is how our BMCC is set, to the manufacturer’s revised specifications.
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John Brawley

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Re: Flange distance and back focus?

PostMon May 05, 2014 12:51 am

Mark2929 wrote:BM did make the mount correct in the first place using CN-E lenses as their guide

No.

They used the EF mount standard FFD. Not CN E lenses as their guide.


Mark2929 wrote: Had this remained the case My lenses would have worked fine.


While many many wide wide angle canon and non canon users lenses wouldn't be able to hit infinity.


Mark2929 wrote:They then overcompensated for the tokina 11-16mm which was out


No.

That was a lens that commonly showed up as not hitting infinity, but if you search these and other forums, you'll find many lenses especially wider angles one wouldn't hit infinity, including Canon lenses.

The Tokina already had a bad reputation for not even hitting infinity on many bodies before the BMCC was introduced.

Mark2929 wrote:As a result of this no witness marks on pro lenses would ever be right.


Well no lens witness marks were ever right anyway on any stills lens. Unless you had a Zeiss CP or a CN-E lens in EF mount that was collimated to the target body. Witness marks on most still lenses are incredibly minimal and most don't even have lines for their distances.

Mark2929 wrote:However that hasn't stopped BM from plastering pictures all over their advertising buff using CN-E lenses


And there's nothing at all stopping you from using those lenses Mark. You can also use them with the correct witness marks by collimating your lenses to your body, something that's been SOP in PL mount lenses and cameras for many decades. You could also mark up and laminate a follow focus disc with the "right" markings as well, something many 1st AC's do with lenses that don't have good markings.

Mark2929 wrote:You're right I could get my lenses collimated for BM's wrongly sized EF mount and then recollimated again if I buy another camera in the future.


Yep. That's exactly what you do and what many others do with PL lenses.

Mark2929 wrote:Yes BM got slated for those lenses wrongly made and with infinity issues so lets not mention that Lets blame the idiot who went out and spent all he had on a set of pro lenses That's far better isn't it.


Well Mark, did you actually do the research ? You don't seem to understand that it's normal to have to collimate lenses for each camera. I just spent a week in testing. Two of those test days was testing each prime and zoom lens on the bodies I have so that I could be sure they'd all hit their marks. These are Panavision Primos, which have shot countless amazing films and won many academy awards. We still rejected a few.

I'm not blaming you but you, yeah you're kind of ignorant of what normal practice is for cinema lenses. Maybe take the hit for a second and get on with what you can do about it. Like I said, you can easily collimate your lenses to work with your body. It doesn't take long to do.

Mark2929 wrote:
Yes the CP2's are shimmable with a kit and instructions how to do it So no problem there then.



Indeed. If you've only just received your CN-E lenses perhaps you may be able to return them if this is so important to you. In my opinion the CP's are the equal optically to the Canon CN-E's from what I've seen (and I've shot both) and you have the advantage of interchangeable mounts that are user shimable.

CP's are more future proof and will allow you to grow into other cameras and mounts. EF is a closed system that has little chance of growth.

Mark2929 wrote:After testing ALL my CN-E lenses now match with two layers of thin tape.


As I mentioned, a terrible solution that will not be consistent over time.

Mark2929 wrote:
A lens can be OUT but still hit the right witness marks on a body that's also out.

Two wrongs make a right?


Yeah they sure can if the lens collimates and the witness marks line up. Absolutely.

Mark2929 wrote:
Putting your specific issue aside for a second, the EF lens mount is highly problematic.

No its not Its only problematic when information is not given Like for example "Buy a BM camera and use the worlds best lens crafters


You keep referring to canon as the "worlds best lens makers". You're making this a very emotional argument. Lenses are highly subjective.

Mark2929 wrote:but dont forget we made the mount to cater for the lens most out so your witness marks wont work and you will need to recollimate your lenses so their not accurate to the EF spec.


Yeah. That's exactly what you need to do. Collimate your lenses to the camera so your witness marks line up. You'll also find they are probably closer to accurate on any other EF mount camera you care to use.


Mark2929 wrote:Yes but BM cited using Canon CN-E lenses and indeed made the EF mount using them as a reference. Only changing it after complaints fromTokina users who also seem to have issues with the canon c300



Mark. you've answered your own issue. BM show a range of lenses on the camera. You can use the CN-E lenses on the camera right now. If you want accurate witness marks then get the lenses collimated to your camera. Just like you'd have to do if you bought a C300 or a 5Dmk3. And it wasn't Tokina users. It was a lot of users with canon lenses under 50mm.


Mark2929 wrote:No the reason witness marks cant be used on the EF mount is because the mount is out.


No.

It's because the lenses often don't even have witness marks, don't have any more than three distances, only have 20-30 degrees of rotation before a clutch engages an infinite rotation ring that means you can never accurately repeatedly pull to them, plus their super lightweight loose construction means that even if the mechanical coupling was accurate they never land in the same spot anyway.

Mark2929 wrote:Initially BM made the mount according to the EF spec.


And then many many many user complained so they matched what CANON ALREADY DO and shortened their mount.

So far, in 2 1/2 years you're the only guy I can think of that has complained about this.

Yes. You're right. Yes, if it was at spec and the CN-E lenses were at spec then the witness marks would line up. No canon camera does this. Why should BM, at the expense of the rest of their users ?

Instead, do what we've been doing for years and collimate your lenses to the camera. You have in effect already done this with your bit's of tape.


Mark2929 wrote:
This allows Canon to make lenses less expensively with less precision.

Not so with their CN-E lineup though.


Indeed. You're starting to come to grips with why cinema lenses cost so much.


Mark2929 wrote:That was the reason they introduced the M4/3 mount Or at least it should have been.


Correct. That was the fastest way for them to get to PL mount, which would allow shimming, plus allow a lot of other vintage lens options.

Mark2929 wrote:No they shouldnt screw other users They should screw me instead. I think where the problem lies is the advertisement guff and the lack of information


Well like I said Mark, anyone who's worked around cinema lenses knows about shimming and the need to check it. Research. The onus is on you to do that research and be informed. You could have asked here for example and I would told you to seriously consider not buying CN-E lenses in EF mount for exactly these reasons.

Mark2929 wrote:
Yes I understand they needed to please those buying the cameras and I agree But just not with the way they did it. You see if I had known this I would never have bought the CN-E lenses.


Well as I've just said, I wouldn't either.

Mark2929 wrote:
BM could though get their factory to make a flange plate that is the correct thickness and sell it to us. Although you believe BM's mistake however good intentioned should be my problem.


It wouldn't work Mark. Did you look at the shim sizes ? They are measured in thousands of a mm.

You could try asking BM to reset your mount with a "correct" FFD, though that would then mean any other EF lenses would probably have trouble on your camera hitting infinity below 50mm. I imagine if you plead with them you might be able to do this, but I don't think it can be done retrospectively. It has to be set during manufacture.

Mark2929 wrote:
I think it would very helful if BM could make a flange plate of the correct thickness.


Which won't work because it's too thick.

Mark2929 wrote:Well At least you didnt call me a liar! Its a workaround for now. Thanks BM.


Where have you been called a liar ?

Mark2929 wrote:Whatever the thickness and I believe it is far more than a few microns It could easily be done by BM's factory Not a piece of ultra thin metal But a properly sized flange plate to replace the old on Just unscrew it and screw your new one on,


Like I said Mark. They measure shims in thousands of a mm. The act of tightening a screw on a sheet of metal is enough to change the FFD. metal is too thick. Most shims are made of poly / plastic.

Mark2929 wrote:
It commits you to a mount that usually can't be shimmed and has other issues with use in motion imaging. For example, you'll find that a heavier cine lens will rotate int he mount when used with a follow focus. There is no way of locking the rotational torque that that follow focus introduces on the lens.

So you're saying I couldnt get my CN-E's collimated anyway


No. Not at all. I'm saying theres ANOTHER issue with using EF mount lenses. Collimation aside, the lens will move in the EF mount because a large diameter focusing ring on a large lens driven by a follow focus has enough leverage to rotate the lens in the mount.

Put any EF lens on your camera and grab it like you're about to have a pull. Then rotate clockwise and counter clockwise. You'll notice it MOVES. That means image shift in your image

Mark2929 wrote:
Really? So why does the lens lock into place on the BM mount?



It locks in, but you can still rotate it in the mount.

Mark2929 wrote:I prefer the CN-E's as they are sharper better colour rendition and open wider.


And so the price you have to pay, like for any cinema lens, is to get the lenses collimated if you want the witness marks to line up. Or the camera. But you can't shim an EF mount camera.

Mark2929 wrote:No Vitriol coming from me JB Just a request to BM for a new flange plate that works to the correct tolerances so I can use the lenses they advertise the camera for in a professional way


Yeah there is mate. You're the one who calls people for trolling. You yourself have shown you're totally ignorant about using cinema lenses, issues of collimation and shimming lenses. You've googled a few documents and you're argumentative to those that are trying to explain the complex issues of lens camera body interoperability. Your solution also reveals your ignorance of how lens collimation works. It's fine....I'm really not trying to be insulting, but you keep aggressively responding and banging the table when someone tries to explain any of the detail.

All of your responses show only knowledge gleaned from reading someone's posts from a blog (most of which is wrong). You're not speaking with any previous experience. I do. With both the issues being discussed and how they pertain to BMD specifically.

I actually almost never ever respond here any more for exactly this reason. I've spent over an hour of my own time the day before I start shooting to tell you what you can do to fix the problem. Because it's not the solution you want to hear all I get back from you is agro.

This is precisely why I don't generally bother to engage anymore. Mostly I get told my opinion is biased towards defending or apologising for BM. I'm certainly not the be and end all of lens mounts and knowledge. But I've addressed your issue and told you the painful truth. I truly empathise with your position and can understand why you'd be upset.

I actually felt your pain as I'm sure you've spent a bucket of money on lenses and you want them to work. I was only trying to help mate.



Mark2929 wrote:When Blackmagic designed the BMCC, they designed it to match with Canon’s cinema lenses.


No.

They designed it to work with the EF mount and they've done it to maximise the compatibility with the vast majority of EF lens users. Unfortunately that's not you right now, but doing what we've done for decades, you can collimate the lenses to work with your body perfectly.


Mark2929 wrote: These lenses are pricey, and made to much more exact measurements than Canon’s photo lenses, even their L series.


And are designed to be re-shimmed.....


Mark2929 wrote: Most of the high-end lenses with EF mounts have very precise focus marks on the barrel. They stop at exactly infinity.


Yes. They have hard stops, unlike most other EF canon still lenses which focus past infinity. Yes, they have better witness marks and more of them. And they are designed to be re-shimmed.


Mark2929 wrote:So they performed a recall, and every lens mount they made afterward was adjusted to allow for the wider tolerance of photo lenses. This is how our BMCC is set, to the manufacturer’s revised specifications.



No.

They didn't perform a recall.

They allowed people to return their cameras if they could show that they weren't hitting infinity. Not the same as recall.

JB
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Re: Flange distance and back focus?

PostMon May 05, 2014 2:01 am

I have no real input to this thread but I'd like to thank all the posters, especially John for the very informative discussion. I didn't know tolerances were so tight.
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Re: Flange distance and back focus?

PostMon May 05, 2014 5:39 am

I want to take issue with the word professional First of all John Thank you for replying Your post was helpful in helping me understand your position through your own professional work re these lenses I now understand that you wouldn't use a follow focus on an EF mount Weirdly I haven't had the problem you describe of movement But I will now further test to see if I can replicate this. If so this is beginning to build a picture of the EF Mount being completely unprofessional and unusable and so is wongly described by BM who seek to please all by making the EF mount short enough that all unprofessional cameras can work with it as well Further adding to its uselessness.

John far from calling you a supporter of BM I would say you are not In fact you are supporting the argument that the BM4K is Unprofessional and not fit for use in a professional environment. I'm sorry you feel my posts are angry and full of vitriol That is not the intention The reason it may come over that way to you is because Posts directed at me have been this way and I have had to answer them back. In other words don't shoot the messenger.

1) The CN=E Lenses at 3500 a pop should not need collimating and are set to fixed tolerances. Of course as they get older this may need to be done But not when they are brand new.

2) BM 4K EF mount throws out the witness marks and C/U focus on professional lenses FULL STOP.

3) All those buying a BM MUST KNOW You will need to get all your lenses collimated unless you own a Tokina 11-16mm which case your good to go.

4) IF like me you have a camera with 40 stuck/hot pixels and an EF Mount that throws out witness marks that you bought Pro lenses for You've been framed.

5) Don't come on the BM Forum as you will further add to the misery by having all blame heaped on yourself for not being professional enough to realise all CN-E Lenses must be Collimated for use on a BM camera.

6) Don't try to present solutions as they will be seen as a weakness in your argument.

7) When BM say professional They mean If the forum BM supporters are to be believed you must be a professional to fix what's wrong with the camera yourself.

From what has been said I have chosen the wrong camera and the wrong lenses for professional use. I've onlywasted about £10,000 believing in BM to be a solution So thanks guys for putting me wide. Hopefully now anyone else wishing to use the BM4K camera and CN-E lenses wont be so dumb.
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Re: Flange distance and back focus?

PostMon May 05, 2014 6:10 am

dude, ya'll need to chill out.

It's simply that the EF mount was originally designed for multiple stills cameras, not for video.

The BM cameras can be used in a professional setting, but like all cameras they have specific quirks (for example, RED One's require Blackshading before use - something I haven't seen on any other digital cinema camera so far).

Any camera can be used in a Professional setting as Professionalism isn't something designated by equipment but rather how you conduct yourself.

You found a solution to your problem, That's awesome. If you maybe talk to a BM Rep about it later they could take it as constructive feedback.

What John says about the EF mount is (unfortunately) correct, however: I don't feel anyone should be that angry over something that small not working. Sure the witness marks are off, most of the AC's I've worked with don't end up using the witness marks knowing that if you're looking at the witness mark rather than your subject you'll miss more subtle movements or the pace of their movement that will throw you out of focus. It's a convenient feature to make an ACs job easier.

What's more important about Cinema Lenses is that they are Consistent (T-Stops are far more precise than F-Stops) which for multiple lenses used in the same lighting setup is a majorly helpful thing, as well as the fact that they don't tend to change focal lengths as you focus.

I'd Kill to own a set of proper Cinema lenses right now (I would buy the Zeiss CP2's however as I am not a huge fan of Canon as a company in the video world), Hell if I had Rokinons I'd at least have focus gears on my lenses that are permanent (I'm working on adding some to my Nikkors - if anyone has a low-budget way to do this let me know!).

It's nice to see I'm not the only one leaving walls of text.
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Flange distance and back focus?

PostMon May 05, 2014 7:25 am

You've come onto a user forum with a problem. We, users, have taken time out to try help you with this issue but you simply shoot us all down because it's not the answer you want.

So why bother posting on a user forum???

Have you contacted BM support directly?
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Re: Flange distance and back focus?

PostMon May 05, 2014 7:58 am

Dustin,

The witness marks don't work because BM's mount is to short.
Now a NEW problem has been bought up by JB IE You cant use a follow focus because the lens moves in the badly designed EF mount. Unless you do away with rack focusing altogether.

Even if you bought CP2's you still cant rack focus. Or even use a follow focus with any lens to rack focus and yet you maintain this is professional.

Do you understand the word professional? The focus puller is no longer needed as he cant pull focus and all CN-E lenses need collimating even though they are not designed to be.

By the way. I'm not angry at all As MY follow focus seems to work fine. Also The witness marks are a disappointment but not the end of the world. I can still focus using the monitor. I cant focus up close though unless I get the BM4K collimated. Its some of you out there I'm worried about who are having real issues with follow focus and communication as I seem to have a camera that works in that regard and I would like to get BM to address the issue of witness marks being out and a workaround that includes a flange plate accessory.

Guess we got sidetracked from MY issues onto the needs of some here who need to vent their anger at those with problems looking for solutions.
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Re: Flange distance and back focus?

PostMon May 05, 2014 8:20 am

adamroberts wrote:You've come onto a user forum with a problem. We, users, have taken time out to try help you with this issue but you simply shoot us all down because it's not the answer you want.

So why bother posting on a user forum???

Have you contacted BM support directly?


We users? Do you speak for everyone or is this just those who like to take the subject off the issue (IE A Solution) and onto their own pet peeve and slam those unfortunate enough to bring problems here? Maybe you could agree about the flange plate as an accessory. Although you have zero knowledge of the BM EF mount as you don't have a BM camera with an EF mount.
Painting me as an angry aggressive idiot as opposed to someone who wants a fix is just a way to stop any progress on getting a fix and diverting it to your fav topic which is hating on the EF mount and on posters taking issues with BM.

The question is what are you doing here? So far from a vocal few I've heard the EF mount is pretty much unusable and yet professional with quirks that all cameras have. That seems to be the direction you and a few want to take this. Have your cake and eat it. So BM are professional but not professional I am the villain of your lovely forum and so what next? Get me banned Don't talk to me Paint me even more as a jerk?
The only people that are coming off that way are those acting as jerks.
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Re: Flange distance and back focus?

PostMon May 05, 2014 10:16 am

Mark2929 wrote:We users? Do you speak for everyone or is this just those who like to take the subject off the issue (IE A Solution) and onto their own pet peeve and slam those unfortunate enough to bring problems here? Maybe you could agree about the flange plate as an accessory.

Where have I taken this off topic??? I've pointed out the flaws of the EF mount which is where your issue lies. I've suggested you test your lenses on other EF mounts so you can see how much they actually vary. I've suggested that as you can't shim the mount you could solve your issue by shimming your lenses to meet your cameras mount distance.

All pretty helpful suggestion at dealing with you problem, no??

Mark2929 wrote:Although you have zero knowledge of the BM EF mount as you don't have a BM camera with an EF mount.

How have I got zero knowledge? I own an original BMCC EF, BMPCC and a BMPC4K, among other cameras. I've also used Canon DSLRs and C100/300's, Sony F3/5/55, etc...

The EF mount is horrid. But its mass market and that's why it's used on so many low cost video camera.

Mark2929 wrote:Painting me as an angry aggressive idiot as opposed to someone who wants a fix is just a way to stop any progress on getting a fix and diverting it to your fav topic which is hating on the EF mount and on posters taking issues with BM.

Where have I painted you as an idiot. I've been trying to help you understand the issue better so you can make educated decisions going forward. The issue is nay as simple a having a plate as an accessories.

Mark2929 wrote:The question is what are you doing here? So far from a vocal few I've heard the EF mount is pretty much unusable and yet professional with quirks that all cameras have. That seems to be the direction you and a few want to take this. Have your cake and eat it. So BM are professional but not professional I am the villain of your lovely forum and so what next? Get me banned Don't talk to me Paint me even more as a jerk?
The only people that are coming off that way are those acting as jerks.

???

What am I doing here??? I'm a user of the cameras. I come on here to try help other, like yourself, get the most out of the cameras.

I'm not hating the EF mount, I'm a realist and understand its limitations.

Why would I want to get you banned? I'd much rather get you out there shooting and using the gear you've spent a fortune on.

The BM cameras are affordable alternatives to the Arri Alexa, RED Epic, Sony F5/55. BM choose to put an EF mount on these cameras as most people who can't afford an Alexa/RED certainly can't afford PL cine lenses. This means they can use affordable EF lenses and get a professional image. Doing this mean we have to deal with compromises. The EF mount is not a "Professional Cine Mount" and any professional camera op/DOP/cinematographer would know this.

John has gone into great detail as to why. No need to repeat it all.


As for the rack focusing issue with the EF mount. This is addressed on the Zeiss CP.2 lenses as Zeiss includes a lens support threaded hole in the EF and MFT mount. Once the lens is mounted you attach the lens support to your rails and the lens can no longer rotate in the mount. I'm surprised Canon never did this but I guess they only assumed the CN lenses would only be used on the C500 or RED Epic that has a locking EF mount.
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Re: Flange distance and back focus?

PostMon May 05, 2014 11:14 am

Mark2929 wrote: I now understand that you wouldn't use a follow focus on an EF mount


I didn't actually say that Mark.

I pointed out a known problem when using large CINE lenses with big focus pulls on regular EF mount bodies.

It doesn't mean you can't use a follow focus and I didn't actually say that you couldn't. You keep on drawing these over reaching conclusions to support your own hostility towards your own choice of buying EF mount cinema lenses.

Mark2929 wrote:
John far from calling you a supporter of BM I would say you are not In fact you are supporting the argument that the BM4K is Unprofessional and not fit for use in a professional environment.


Mark.

I'm a professional. I make my living as a cinematographer. I use the camera you're describing as "unprofessional" most days. I use it often alongside cameras costing a lot more. Sometimes I shoot entire scenes using only this unprofessional camera. Those scenes get broadcast on a major free to air commercial broadcaster.

Again, you're reaching. Yeah the EF mount is unprofessional and a crappy legacy mount. I've listed why it's unprofessional and they were reasons you don't even know about. And yet here I am, dealing with it and embracing it for what it does give me and can do for me.

That's what being a professional is.

Mark2929 wrote:
1) The CN=E Lenses at 3500 a pop should not need collimating and are set to fixed tolerances. Of course as they get older this may need to be done But not when they are brand new.




This is just so wrong Mark. you have to let go of this idea that the lenses come to you in some perfect way made by unicorns in the canon factory. Cine lenses are designed to be shimmed. Let's call it optimised. They are designed to be optimised to your camera. They are still the same awesome cine lenses you bought. They aren't affected in any way at all optically. They are actually made even better by being "optimised" because their witness marks will also now be accurate. More than likely they'll also be more accurate for any other EF mount camera you plan to use.

The "optimisation" they are on now is a generic standard that no one actually cares about.

Mark2929 wrote:
2) BM 4K EF mount throws out the witness marks and C/U focus on professional lenses FULL STOP.



Yes they do. Just like every other single EF mount camera made by Canon.

Mark2929 wrote:3) All those buying a BM MUST KNOW You will need to get all your lenses collimated unless you own a Tokina 11-16mm which case your good to go.


You're still hung up that this was done for the sake of one lens. I've said, twice already, that it wasn't just the Tokina. It was most lenses below 50mm, irrespective of the brand, but it was especially bad with the Tokina, which was a popular lens because many wanted it for the full frame equivalent focal length it offered.


Mark2929 wrote:4) IF like me you have a camera with 40 stuck/hot pixels and an EF Mount that throws out witness marks that you bought Pro lenses for You've been framed.


Mark, just let go of your conviction that the lens has to stay with the same collimation it has now and everything will be awesome. I promise.

Mark2929 wrote:5) Don't come on the BM Forum as you will further add to the misery by having all blame heaped on yourself for not being professional enough to realise all CN-E Lenses must be Collimated for use on a BM camera.


Don't sulk about a decision that you've made and then refuse to take the solution that offers you no real compromise in what you're trying to achieve and then denigrate the several people that spent time over multiple posts trying to show you how you could achieve what you want in the first place. Be professional.

Mark2929 wrote:6) Don't try to present solutions as they will be seen as a weakness in your argument.


By all means offer up solutions. Your flange plate adaptor isn't a solution, it's been explained why, and you don't seem to want to accept that it won't work. Prove me wrong and make one yourself. I'd love to be shown up and that's how innovation happens.

Mark2929 wrote:7) When BM say professional They mean If the forum BM supporters are to be believed you must be a professional to fix what's wrong with the camera yourself.


Again, because we talk about solutions that aren't what you want to hear, we're "defenders' or "apologists". It's really ******* tiring mate to keep on banging on with that tired old trite. Seriously it's such a boring non argument. And again, all you do by throwing that out there is make me never ever want to post to help anyone like you in your situation. Would you prefer to still be where you were at post 1 ?

A whole bunch of well establish and experienced users shared their views, which you invited them to do by posting in the first place. It's really rude to then slag people off because you don't agree with their views and responses.

Mark2929 wrote:From what has been said I have chosen the wrong camera and the wrong lenses for professional use. I've onlywasted about £10,000 believing in BM to be a solution So thanks guys for putting me wide. Hopefully now anyone else wishing to use the BM4K camera and CN-E lenses wont be so dumb.


Mark, with one simple step.... letting go of your notion that the "Optimisation" your canon lenses currently have is somehow perfect and should never be adjusted, you can go back to where you hoped to be when you bought the lenses.

This "optimisation" is something I do at the beginning of every major shoot I do, be it a one day commercial or an 8 week TV series. It's standard operating procedure.

Collimate your lenses to your camera, and the problem is solved. You lenses are back to being awesome again. As they should be....

JB

* Optimisation really means collimation.
Last edited by Tony Rivera on Wed May 07, 2014 4:55 pm, edited 1 time in total.
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John Brawley
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Chiaroscuro

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Re: Flange distance and back focus?

PostMon May 05, 2014 12:22 pm

Mark2929 wrote:Why cant BM make a slightly thicker flange plate as an accessory so we can put a new one on that is made for lenses that are not out.


This: Ask Blackmagic Design directly (as mentioned). JB, Adam & Tom have all attempted to help you by sharing their knowledge and painting a realistic picture of how things are but also offering possible solutions to your problem.

I can honestly state that my opinions are objective in this matter: I am very critical of some aspects of my BMPCC and I certainly don't agree with everything people make off as fact on this forum. However, your arguments seem unreasonable and maybe fuelled by great disappointment.

I for one appreciate their knowledgeable contributions (although I don't always agree).

In your own words, "don't shoot the messenger".
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Re: Flange distance and back focus?

PostMon May 05, 2014 3:18 pm

Going back over the posts I may have been a bit harsh while I overcome the lack of professionalism inherent in the equipment and I apologise for that. But then I was right to be defensive over some of the answers given and for that no apology is offered.

John, some of your writing seems to be with caveats you later backtrack or ambush with. If you say something it is only right I may take issue with certain statements. However I thank you also for some of the insights you have given.

I must admit I still cant quite believe the limitations on the EF mount and on the fact I cant use the witness marks on my lenses without having them or the camera collimated.

Adam Actually the CN-E'S do have an accessory you can purchase to hold the lens onto the rails. I thought this was to hold the weight I expect its for both.

Anyway lots to think about now and who knows maybe BM will come up with a solution for the BM EF back focus.

For me the preferred solution is to focus using the monitor now.
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Peter J. DeCrescenzo

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Re: Flange distance and back focus?

PostMon May 05, 2014 5:01 pm

Thanks, JB, for your detailed posts. Very informative. Cheers!

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Flange distance and back focus?

PostMon May 05, 2014 5:22 pm

Mark2929 wrote:I must admit I still cant quite believe the limitations on the EF mount and on the fact I cant use the witness marks on my lenses without having them or the camera collimated.

Even high end PL mount lenses costing over £30k and Arri Alexa cameras need to be collimated. That is why the PL mount is designed to be shimmed both on the lens and the camera. Rental houses check and adjust cameras and lenses all the time. A simple hard bump could put the witness marks out.

This is why it's not that simple for us to just swap the mount for one that is to spec.

Mark2929 wrote:Adam Actually the CN-E'S do have an accessory you can purchase to hold the lens onto the rails. I thought this was to hold the weight I expect its for both.

Get it. It'll pretty much eliminate the rotation of the lens when pulling focus.
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Re: Flange distance and back focus?

PostMon May 05, 2014 9:48 pm

Thanks, John. Learned a lot from this exchange. I retract my request that BMD reply to tell us the flange focal distance on the BMPC4K EF and the URSA EF. I think it's been answered in this exchange. As I said much earlier in the thread, they are going to sell more PL mounts with this understanding. And I understand even the PL mount can require collimating the lenses.

Thanks, again, for all your contributions and extreme patience. We miss your presence here but enjoy when you can drop by.


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Last edited by rick.lang on Tue May 06, 2014 3:28 am, edited 2 times in total.
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Re: Flange distance and back focus?

PostTue May 06, 2014 1:13 am

Mark, your main gripe seems to be that you cannot reliably use lens witness marks to set focus using a tape measure. You have found that by increasing flange depth by the use of a sticky tape shim witness marks become more accurate and from this you assume that the flange depth on your camera is too short. I have been through a similar exercise recently and for a while I assumed that my BMPCC’s flange depth was short. It turned out that I was wrong. I was wrong because I had not located accurate information beforehand.

If I was working on your problem I would start by testing the idea that using witness marks and a tape measure were a good way to set focus. I realize that your marks are not accurate but I am sure that you could make temporary marks of your own by using a write-on sticky tape for example. I would then check how reproducible the results were when I returned focus to my chosen witness mark. I would check for the effects of backlash by approaching the witness mark from either direction. I would compare my results with those obtained by using the camera viewfinder or field monitor or autofocus if available.

If my results showed that tape measure and witness marks were the way to go I would look for a better way of making and displaying witness marks.

When I suspected that my BMPCC’s flange depth was short I took my camera, collimator and lenses to the technician at the local BMD agent who is conveniently located close to my address in south-eastern Australia. His only suggestion was to send my camera back to BMD but as I was not using a ‘BMD approved’ lens I could not expect much sympathy. It would have been a great help if the agent had a trusted test lens. A rather disconcerting outcome of my trip to the agent was that I was told BMD build some ‘give’ into their mounts. As short is better than long I assume their ‘give’ is on the short side. I have enquired as to the amount of this ‘give’ but as yet I have no reply.

I believe that you have read my thread on my BMPCC flange depth issue. I solved my problem by modifying an adapter so that it was slightly too long and then shortening it in a series of steps of 0.0005” at a time. It was a tedious process as I had to reassemble the adapter after each shortening until the witness marks and parfocality corresponded. Are suggesting that BMD market thicker mounts in say 0.0005” rises? If available which one would you choose?
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Re: Flange distance and back focus?

PostTue May 06, 2014 1:29 am

WOW!
I feel like I owe someone tuition money!

I don't think I could have gotten a better grasp of this info even if I was with you guys on set in the real world while your explaining what your doing in real time.

Thank you for this, even if this will not apply to me until later down the road... way later.
But I will still put it in the brain bank for a withdrawal in the future.

As for the money I can't send any to y'all on count of I'm a bike mechanic and junior film maker who spends it all on bikes and camera gear.

But seriously, thanks I've learned a lot in the past few months just ghosting this forum.
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Re: Flange distance and back focus?

PostTue May 06, 2014 2:59 am

It's unfortunate Mark hasn't got the answers he's looking for, but through his persistence, I have learnt a great deal from this post. Thanks John, Adam and Tom.
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Re: Flange distance and back focus?

PostTue May 06, 2014 3:28 am

Adam and Tom, thanks for your gentle persistence in this thread. Appreciate the generous spirit in which you share your knowledge.

There sure is a lot more to cinematography than a layman would think! I wonder if there's any kind of equivalent to film school on the iTunes Podcasts. There's a ton of accredited university courses available online, but would be very interesting to know where to pick up more of this knowledge besides the school of hard knocks. I am in complete sympathy with Mark who felt Canon CN-E lenses would allow him to use the witness marks on an EF mount. It seems reasonable to me but it's not the reality as we've learned over the last few days.

More to digest in determining which camera and mount is appropriate for my abilities. Maybe the Sony A7s? But I swore off 4:2:0 because I know from experience, it doesn't always grade well. So then you must buy an Atomos recorder that costs more than the camera and that means you end up needing a rig and by the time I'm done thinking about that, I'm back where I started, in the World According to Grant. My wife says just buy the Pocket! She's always able to see the forest when I only see the trees! So many trees to see


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Re: Flange distance and back focus?

PostTue May 06, 2014 7:02 am

rick.lang wrote:Adam and Tom, thanks for your gentle persistence in this thread. Appreciate the generous spirit in which you share your knowledge.

No problem. I just wanna help people get the most out of what they have. It'll only improve the craft all round.

None of this solve Mark's issue but I hope he, and others, have the info to understand the issue better.

None of this kit is perfect but today we have access to more than we ever did at lower cost than we ever imagined.
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Mark Davies

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Re: Flange distance and back focus?

PostTue May 06, 2014 12:23 pm

Well Seemingly Canon disagree with what is being said.

This from Canon

Also with regards the shims for your lens I have been told by our head office that we are unable to supply the shims as it would affect the lens back focus and therefore be incorrect for the canon camera that is was designed for. They suggest contact the camera manufacture for them to have the mount at the correct focus position for a camera.


Clearly Canon are saying they make the CN-E's to the EF mount spec and the witness marks will not be out if using their cameras Now that might mean their professional cameras only. But then that's what BM call their new 4K camera and those soon to be released Along with a whole lot of advertising showing the Canon CN-E lenses attached to their products.
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Re: Flange distance and back focus?

PostTue May 06, 2014 9:15 pm

Another email from Canon re this.

The lenses are set up in japan using the correct back focus, and therefore this will give you the correct focus position on the lens. If you were to alter this for another camera then put that lens on to the C500 etc the back focus would be incorrect so you would have to adjust it again.
If you wish to adjust your lenses then that is your choice. But the lenses are correct for the EF mount back focus position.


This backs my earlier expectations that the primes are set up properly and unlikely to be out as they are factory set with no Canon provision for adjustment and a recommendation they shouldn't be.

So according to Canon I can use these lenses on their professional cameras and any camera with the correct mount dimensions.
I would guess Canon have had few complaints about lenses that cant focus to infinity on their professional camera lineup.
I have to now consider what JB has said against what Canon are saying and I really cant see how Canon could get away with selling pro unshimmable primes with pro cameras and get away with it to the point they could give me that response.

This has to be another error on BM's part who altered the mount in order to please less than professional lens users. Although understandable it also catches out those who took them at their word that the camera was professional.
Mark Davies
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