BMPCC4K Gets blurry when zooming

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jimrage

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BMPCC4K Gets blurry when zooming

PostMon Dec 17, 2018 9:52 pm

Hello I've got a 4k Pocket cam with a
"Metabones Speed Booster Ultra 0.71x Adapter for Canon Full-Frame EF-Mount Lens to Micro Four Thirds-Mount Camera." This setup works great for fixed lenses, but any time I put a zoom lens on I have to refocus after zooming. This doesn't happen with my old Pocket Cam (using the Metabones T Speed EF adapter). Did I make a mistake purchasing my speed booster, Or is this something unique?
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John Morris

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Re: BMPCC4K Gets blurry when zooming

PostTue Dec 18, 2018 12:34 am

While I don't know if there could be a problem with the speed booster, I can think of a couple of reasons why you are seeing focus issues. One is that the 4K has a larger sensor and shallower depth of field. The second is that in 4k there is more detail to blur. Also there is the issue that, unless your lens is par-focal, you should be seeing a focus shift from zooming anyway. In other words, the focus shift was still there when using the same lens on the old BMPCC but it wasn't so obvious.
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rick.lang

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Re: BMPCC4K Gets blurry when zooming

PostTue Dec 18, 2018 2:20 am

I wonder if a small adjustment of the rear focus on the SpeedBooster will help.


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Re: BMPCC4K Gets blurry when zooming

PostTue Dec 18, 2018 5:35 pm

Thanks for the replies. I should have stated before that the image doesn't get just a bit fuzzy, it'll go from a perfect crisp image to so blurry that everything is just blobs. Even with a fairly small zoom throw I'll end up with a completely out of focus image.

Adjusting the rear focus is a good suggestion, but I'm a bit cautious after reading an article from Metabones about it (sorry this forum won't let me actually a link to it.) They say to only adjust it if you can't focus on infinity, and I have no problem doing that, it just won't stay in focus.

I've sent a message to technical support at Metabones. I wish I had a MFT zoom lens to test out as well in case this is on the pocket camera's side.
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Re: BMPCC4K Gets blurry when zooming

PostTue Dec 18, 2018 7:10 pm

Sound like a lens issue to me, which Canon lens are you using? How is the focus/Zoom on a Canon Camera, or without the SB?
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jimrage

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Re: BMPCC4K Gets blurry when zooming

PostTue Dec 18, 2018 7:18 pm

It happens with ever zoom lens I use. When I pop them on a different camera they're fine.
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Re: BMPCC4K Gets blurry when zooming

PostTue Dec 18, 2018 7:25 pm

Follow the article on Metabones site and adjust the back focus. That's what I did with mine, and my zooms now stay in focus as you zoom. All my lenses still hit infinity, so it hasn't negatively impacted that either.
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Re: BMPCC4K Gets blurry when zooming

PostTue Dec 18, 2018 7:55 pm

Then it is the SB. You could try adjusting it, OEM return itmif you gotmnit new for a replacement. If new, i would do the latter.
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jimrage

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Re: BMPCC4K Gets blurry when zooming

PostTue Dec 18, 2018 8:34 pm

Thanks everyone! It gives me more confidence to try adjusting that screw hearing that someone else has given it a whirl. I'll let you know how it turns out.
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rick.lang

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Re: BMPCC4K Gets blurry when zooming

PostTue Dec 18, 2018 10:29 pm

Something to keep in mind that there are different tolerances possible on the dimensions of any device that ultimately affect the flange focal distance as perceived by your lens. Always a good idea to be able to adjust that FFD either through a back focus or shim on the lens or the adapters. One of the benefits of using PL lenses, but not restricted to PL lenses. It’s very good Metabones provides that option on their adapter, as does Wooden Camera and SLR Magic on their professional PL-mFT adapters.


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Re: BMPCC4K Gets blurry when zooming

PostWed Dec 19, 2018 7:03 pm

Try as I might I couldn't get that rear element to budge. If you google Metabones and "infinity-adjustment-speed-booster-only" you'll find the article I was following. I've got an Ultra speed booster and I found the recessed screw they were talking about. I loosened it to the point that it fell out. I found another screw that looked similar to the one in the diagram and took that out also. Still no dice. I pushed hard enough on the housing around the lens that I left a scratch (not to pleased about that, but it doesn't seem to have done any damage to the optics.) Metabones still hasn't responded to my email. Am I hopeless or just cursed?
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Re: BMPCC4K Gets blurry when zooming

PostWed Dec 19, 2018 7:22 pm

Also thanks rick.lang for the shimming idea. I think you're on the right track. I googled shimming the Metabones itself. I don't want to shim my lenses because I use them on other cameras that they work fine on. If you google "shimming-your-metabones-cine-smart-adapter" you'll find an article by Adam Roberts who seems to have had a similar problem.
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Re: BMPCC4K Gets blurry when zooming

PostThu Dec 20, 2018 12:33 am

Good, Adam’s advice is useually Sound, he used to be a regular contributor here.
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Re: BMPCC4K Gets blurry when zooming

PostThu Jan 03, 2019 8:25 pm

SOLVED

So the answer turned out to not be very exciting. I returned the Metabones and exchanged it for an identical unit. The new one works fine. The old one was just defective. Doesn't leave me too impressed with Metabone's craftsmanship or costumer service (they never replied to any of my emails and they don't have a phone number) but the problem is solved non the less.

Thanks everyone for chiming in and helping me troubleshoot.
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Re: BMPCC4K Gets blurry when zooming

PostThu Jan 03, 2019 9:29 pm

Metabones does stand behind their products, it is just getting a hold of them that is problematic, as is SKR Magic. But both make excellent products, even with less than ideal quality control, which BM also suffers from.
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Re: BMPCC4K Gets blurry when zooming

PostFri Jan 04, 2019 3:14 am

Ray, actually the first Metabones Speed Booster was produced in 2013,
Petersburg, VA, USA, January 14, 2013 - Metabones® and Caldwell Photographic jointly announce a revolutionary accessory called Speed Booster™, which mounts between a mirrorless camera and a SLR lens.


So they have only been produced in their first version for five years, and the more complicated versions (Canon EF to MFT for example) only for the last three years. BM released its first Cinema Camera in 2012, and the Pocket Camera was released about one year later in 2013. The original MFT version was an immediate success with Panasonic AF100 and GH2 users. So the Metabones Speed Booster as we know it now, is relatively new, and camera manufacturers that make cameras with varying FFD issues, adds to Metabones Speed Booster issues, and tolerances. What works on one csmera, may not work with another without some tweaking.
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Re: BMPCC4K Gets blurry when zooming

PostFri Jan 04, 2019 6:01 pm

Ray, I agree, manufacturing should be more precise, and have better QC, which adds to the cost. However, I think you missed my point, it that the one issue Metabones can not control the differences with camera manufacturers lens mounts, not being made to the same specification. This is also an issue when trying to get an adapted lens to be parfocal, or have accurate witness marks, unless the adapter can be shimmed or FFD adjusted (as Metabones has done), not going to happen. But we live in a world that is far from perfect, so everything else is not going to be perfect either.

I have owned several Metsbones Speed Boosters, no issues with any of them, other than FFD tollerences.

Even BMs own MFT mounts do not have the same FFD (or same flange thickness) and will throw off what might have been a parfocal Zoom, so it is no longer parfocal without shimming. The FFD on my original BM Pocket Camera was not the same as the Micro Cinema camera, which was different than the Micros Studio Camera, all required a different MFT/PL mount shim set, to get my parfocal Angie zoom to be parfocal on each of these cameras. The adapter was a Wooden Camera Pro MFT/PL adapter. My first test was with the fixed FFD Wooden Camera BMPCC MFT/PL adapter, which worked on the Pocket, but not on the Micro cameras.
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Re: BMPCC4K Gets blurry when zooming

PostFri Jan 04, 2019 10:53 pm

Ray, you are right about number 4. However, Metabones did make different speed boosters for different model cameras, and original generic MFT Speed Booster, the BMCC, BMPCC GH4/5 all had specific recommended SB, for example. But because they can not control variance in camera lens mounts or ca era manufacturing by the various camera makes, they use the published standards or a sample camera for setting the mount. This is why some Pocket Speed Boosters fit tight and sime loose, due to issues by BM to keep the mount consistent. BM also changed the original EF mount in the BMCC when people complained about some EF lenses not hitting inf. focus, which added to the issues with lenses and adapters on those cameras. Metabones is not free from errors, and the OPs SB needed replacement or adjustment to correct the issues it was having.

Thirdly, I don't see how shimming would affect a lens that is truly parfocal. If the lens focuses correctly at one zoom setting, it should do so at any zoom setting, that's what parfocal is about. Unless you're talking about shimming to set the lens at some average point where nothing is critically in focus, but close enough.


First a parfocal Zoom lens is designed to be parfocal with a given lens mount FFD dimension. The camera this parfocal lens is being used on must also have a lens mount FFD that matches the standard being used.

The PL mount is 52mm and Canon EF mount FFD is 44mm, for example. The PL. oh t can be shimmed in most cameras, whereas the Cankn EF mount is fixed. Now, if the Camera Mount is off by as little as 0.020 of an inch, a mechanically set parfocal cine Zoom or any parfocal Zoom (except for zooms that are controlled by the camera electronics) will not give parfocal performance as the “Back Flcus” is off, and the focus will change when you zoom, get this off my a 0.10 of an inch, and the lens will no longer hit inf. focus.

This is pure physics, nothing magical here. So while my copy of the Oly 14-35mm f/2.0 Zoom is giving parfocal performance on my AF100, it might not give parfocal performance on the new Pocket 4K. Is your 14-35 parfocal on your Pocket 4K?

This is why the Cine PL Mount was designed to be shimmed, so the FFD could be corrected and reset back to the 44mm stsndard, and correct for lens mount or camera mount wear, which will also throw off the FFD over time. Stainless steel is being used now to reduce wear issues on these mounts.

This also explains why some Sigma 18-35s will give very close to parfocal performance on some cameras and not on others. It all boils down to what the camera’s actual FFD is and the build quality of thenlens sample, which vary from lens to lens.

There are errors in very type of manufacturing, and expecting error free performance from one company and not another is very un realistic. Even robotic, CNC and other computer controlled manufacturing is not error free. Even the new Nikon Z cameras have bad copies shipped, and need adjustment or replacement.

Nothing is perfect, but we try to be as close as we can. ;)
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Last edited by Denny Smith on Sat Jan 05, 2019 2:01 am, edited 1 time in total.
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rick.lang

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Re: BMPCC4K Gets blurry when zooming

PostSat Jan 05, 2019 1:24 am

Denny, I admire your patience.


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Re: BMPCC4K Gets blurry when zooming

PostSat Jan 05, 2019 2:15 am

Ray, you obviously haver never used a real ENG type or true Cine camera with a parfocal designed ENG or Cine zoom lens. On every ENG camera I have used over the last 30-years, you need to adjust the back focus of the zoom every time you mount it, to insure the zoom is correctly set for parfocal performance. The back focus on a ENG zoom, and the 2/3rds Cine lenses that were made, optically corrects for FFD misalignment. The other way to correct is this is with shims on the lens mount in cine cameras, when used with cine lenses than lack a back focus adjustment.

Every lens made is designed to project an image at a given distance from the rear element of the lens to the film or sensor plane. This distance is incorporated into the Focal Flange Distance (FFD) of a given lens and its mount, and if you change this distance by even a few millimeters, it will not focus as designed, and this includes parfocal zooms.

I am done trying to explain a concept that you are just not getting. Here is a quote from Matt Duclos, who runs one of the leading Cine Lens Service in the USA, with most of his customers in Hollywood and New York.

Focus back on back focus

Back focus is a common term used to describe the Flange Focal Distance (FFD). Or the distance between the rear surface of a lens mount and the film plane or sensor. The most common FFD in my line of work is relative to the Positive Lock (PL) Mount system used on many motion picture cameras and lenses. The FFD for a PL camera is 52mm (2.0472441″) This means that when a lens is mounted to a camera correctly, the image produced by the lens should come to focus at exactly 52mm from the rear of the lens mount. There is a lot of argument about precision calibration in regards to where exactly the image lands. For film and digital, the argument is that the image must land “within” the film or sensor and not on the surface. This is an extremely small amount, approximately 0.02mm or 0.0007″.

Adjustment of the FFD does not usually require moving the actual lens mount but moving the body and glass of the lens forward or backward relative to the film plane. Most mounts are manufactured using reliable solid stainless steel and are precision ground. This allows the mount of the lens to interface with the mount of the camera with little to no variance. Since the locking of the two mounts creates the same distance every time. The easiest way to adjust back focus is to add or remove shims between the lens mount and the body of the lens, effectively moving all of the glass and changing the distance from the rear element to the film plane. This can be tricky because both the camera and the lens have a standard to comply with and sometimes one standard must be broken to obtain proper back focus. All of this is assuming the lens you are using has precise focus marks that require calibration… If not, stop reading now.

Several tools are used to aid in the adjusting lenses as well as cameras. A lens must be set so that it obtains infinity on its mark. This is assuming the lens is marked properly from the factory. To check this a Reflex Autocollimator. I don’t want to geek out too much here, but basically, this tool uses a small test pattern that light passes through onto a corrective lens that makes the light travel in a parallel pattern into the lens in question. The light then travels though the lens and lands on a mirror (film plane) and bounces back through the corrective lens, still parallel, back to a reflex mirror where a technician can inspect the image. Assuming the lens mount of the collimator is proper, and the lens is adjusted properly, a sharp crisp image of the test patter can be seen. Otherwise, adjustment is necessary. The glass of the lens either needs to be moved closer or farther from the film plane so that the focal point is exactly where it should be. As I mentioned before, the easiest most common method for adjusting the distance to the film plane is with shims under the lens mount. Lens manufacturers will design a lens with room to add several shims from the factory so that they can be removed if necessary. The smallest common adjustment is one half thousandth of an inch (0.0005″). A perfectly adjusted lens (relative to infinity) can still be useless if the cameras FFD is improperly adjusted.

In the “old days” of film, adjustment of the FFD on a camera was done only be experienced camera technicians. With the coming of the digital age and cameras such as the RED One, adjusting back focus on the camera has become common practice. A poor common practice in my opinion. There are many tools to determine the FFD of a camera. The most simple and obvious is a depth gauge. Basically a ruler that measures the distance… Easy right? Not so much… I would recommend something a little more scientific. There are a few tools that will be coming to the market soon. Of course you could always use the old wide angle lens trick. This simply requires a wide angle lens that you know is perfectly adjusted. You may ask yourself, why a wide lens? Basically, the depth of focus is far more critical on the film plane with a wide angle lens than it is with a telephoto lens. So the idea is to set the lens on it’s infinity mark and dial in the back focus on the camera while looking through the view finder or a monitor trying to find the best image possible. Sometimes this can be tricky and less than accurate.

All in all, a camera can be adjusted to correct improper back focus in a lens and a lens can be adjusted to correct improper back focus in a camera… But this doesn’t do anyone any good because as soon as you change either variable, you’re going to be searching for a reason why everything is out of focus or your lens won’t reach infinity focus. The camera and lens should be adjusted independently and brought together with proper specs. This is the only way to keep everything calibrated correctly and avoid variance in critical components.
Matthew Duclos


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Jack Fairley

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Re: BMPCC4K Gets blurry when zooming

PostSat Jan 05, 2019 2:55 am

Denny Smith wrote:In the US, we have an expression, “you can lead a horse to water, but you can not make it (the horse) drink.
Good night.

I'll have what he's having. Interesting posts, thank you Denny.
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Re: BMPCC4K Gets blurry when zooming

PostMon Jan 07, 2019 8:50 pm

Hi, I stepped away after my last post thinking this thread was now dead, but boy has it sprouted legs! Anyhow I have to admit that some of the things you guys are talking about make my head spin, but I'll try to provide a little more additional information.

My primary zoom lens is a Canon 24-105. I took some time just now to look into this lens a bit more and there are certainly some varied results out there. I use it on my full frame Canon Mark III 5D as well as my old pocket cam and had never noticed any fuzz. I wouldn't be surprised however if there is a tiny bit of fuzz that I've never noticed if I focus all the way zoomed in on the Mark III 5D and then pull it as wide as possible, but if so, it's fairly negligible.

I also tested out some cheapo zoom lenses that work fine on both the old Pocket Cam and the Mark III 5D, but were way off on the BMPCC4k. When I say way off, I mean totally out. Crystal clear zoomed in, blob soup zoomed out.

The new Metabones I got is great, and would totally recommend, but it's a shame that they sent out an off kilter mount and wouldn't reply to my emails.

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