BMPCC + Speed Booster = shifted focal plane?

Hi,

I´m using a Sigma 18-35 1.8 with a Metabones Speed Booster on my BMPCC.
What I noticed is, that the left side of the image isn´t perfectly in focus while the right side is spot-on.
If I try to get the left side as sharp as possible, the middle of the picture and the right side will be slightly out of focus.

Please take a look at the picture below. Notice how the very left side seems to be quite blurry, while the right side isn´t that bad. The aperture was 2.5.



I´ve tried two Sigma 18-35 and two different Speed Boosters, but the results were exactly the same.
However, if I use a completely different lens (Panasonic 14mm 2.5) without the Metabones SB, everything seems to be fine. This is really strange.

Has anyone else noticed similar effects? What could cause this?

are you on Infinity Focus?

It's possible your speedbooster (much like many on the forums) may need a slight adjustment.

http://www.metabones.com/article/of/infinity-adjustment-speed-booster-only

The lens was at infinity, but the SB is perfectly adjusted. This is my second SB. I have no idea, why the middle of the picture and the right side is fine, while only the left quarter of the image is out of fucus...

That's either a decentered lens element or a misaligned mount.

Probably not a decentered element given you've tried 2 Sigmas and 2 SB's. If it was you'd notice some uneven vignetting WO - that is, if you can notice vignetting.

So if it's a misaligned mount, you have the mount on the Pocket, two mounts on the SB and the mount on the Sigma. However, it's not very likely to be the lens or the SB since you got the same result with 2 Sigmas and 2 SB's. Which leaves the mount on the Pocket. It's possible the increased DOF of the Panny 2.5 is enough to cover up the problem.

If you stop down the Sigma + SB to about 2.5 is the sharpness even across the frame?

If you have another 1.8 or faster lens does it have the same problem?

If you stop down the Sigma + SB to about 2.5 is the sharpness even across the frame?

No, it´s not perfectly sharp. Unfortunately, I have no lens here to compare it to the Sigma, except an identical Sigma 18-35. Both lenses behave the same, there is no difference in terms of focus shift. That´s why I don´t think it has something to do with the lens.

Here is a comparison between F1 and F2.8:

Picture 1: F1 (with SB)


Picture 2: approx. F2.8 (with SB)


Notice how the right side is always sharper than the lift side, no matter the aperture.
The roof tiles of the buildings on the right side are detailed at F2.8 and still sharp enough at F1.
On the left side, you don´t see fine details, because everything is out of focus.
It looks like my camera needs to be checked by BMD...

I have a Sigma 18-35 and a Metabones Speed booster to use on my BMPCC. As it was not a parfocal combination I followed the Metabones adjustment procedure to achieve parfocality. This involves slackening a clamp screw and rotating the lens elements to a new setting and checking focus. I used an autocollimator to provide an infinity target. After I loosened the clamp screw I noticed that the threads were what I would call ‘sloppy’. I would not be surprised if this sloppiness caused alignment problems.

However I did obtain a parfocal combination as a result of my adjustment. Although the combination is now par focal I do not think much of the resulting definition. I took the camera to the local BMD agent and I was told that as the Sigma was not on their 'approved lens list' I probably would not get much sympathy.

Does this happen only with the Sigma, or with other lenses too?
If you want you can come to my office and we do some tests with my lenses on your camera.
We can also check your Sigma on my BMCC. Just give me a call.

Does this happen only with the Sigma, or with other lenses too?
If you want you can come to my office and we do some tests with my lenses on your camera.
We can also check your Sigma on my BMCC. Just give me a call.

Brilliant idea! I would be happy to do some tests. I´ve got some Canon FD glass here, but the results aren´t very informative, as these lenses are quite soft. I sold all my MFT lenses, except for the 14mm pancake.

This is the 14mm at F2.6:


At this aperture, the DOF is large enough to mask the weird effect. With my Sigma at 1.8 (plus SB) it´s very evident, stopped down to about 2.8 it´s not so easy to point my finger at it, but it´s there. Maybe I´m paranoid, but also with the 14mm F2.5, the left side looks a bit distorted, doesn´t it? It´s not obvious, but it just doesn´t look "right". Like a bit of motion blur on the left third of the image, although the camera didn´t move. The right side looks ok to me...

Just looking at these images it's difficult to judge what is going on as they are low resolution and very flat.

Any chance you can share I hight res version?

Also shooting out over a landscape is probably not the best test. Can you shoot a flat brick wall? This way we can see a flat plane that is all at the same distance from camera.

Just looking at these images it could simply be a finder print on the edge of the lens element of the sensor.

The image should be higher res now. There are no finger prints on the sensor, the lens or the speed booster. Maybe I should find a flat brick wall and test again.

The high res images are better to look at. Thanks.

Are you shooting through a window?? The 2 shots of the building look like you are shooting through a window. Could that be causing the issue?

Yes, I was shooting through a window, because of the rain. The window has no influence on the softer left side of the image. Please take a look at the two pictures on top of that thread, they were taken outside in the deep woods with a different Sigma 18-35 and a different speed booster. By "different" I mean the serial number. Please notice how the left quarter of the image is much softer than the right.

Because the left side of the image still looks a bit inaccurate to me, even with the 14mm pancake attached, my BMPCC seems to be the error source. I´m going to pay a visit to Robert Niessner and look how my lens behaves on his camera.

The high res images are better to look at. Thanks.

Are you shooting through a window??

Bingo!

The high res images are better to look at. Thanks.

Are you shooting through a window??

Bingo!

The window has nothing to do with my problem. I took a lot of footage outside in the woods and everything looks exactly the same.

The high res images are better to look at. Thanks.

Are you shooting through a window??

Bingo!

The window has nothing to do with my problem. I took a lot of footage outside in the woods and everything looks exactly the same.

Well it appears you may have a faulty speedbooster. I actually just got one wit the nikon sigma 18-35and it's amazing. It's difficult to see tho in your images. Maybe shooting at a chart will hep determine for sure?

Have you tried a Sigma 18-35 with an optics free adapter and if so did you get the same problem?

Here is an observation that I should have included in my earlier post.
When I was adjusting my Metabones SB to make my BMPCC / SB / Sigma 18 -35 combination parfocal I concentrated on the centre of the image. However it became fairly obvious that at the 18mm setting the plane of focus is curved, if, for example, the image centre is focused at the lens infinity mark the periphery is a little out of focus. To improve focus for the periphery focus setting had to be a little beyond the infinity mark. This may be what you are seeing. It will be interesting to see any brick wall results.

I did not detect the field curvature at the 35 mm setting. This is not surprising as depth of focus issues are more apparent at shorter focal lengths. Is the effect you are observing related to focal length

Thank you all for your help! I´m going to try it with a brick wall today.

@Alastair: Yes, I did notice that the plane of focus is curved, as I wasn´t able to get the center of the image and the periphery in focus at the same time. It´s even noticeable at 35mm, but it´s rather subtle compared to 18mm.

I always thought the speed booster was to blame here, but I´ve got a new one and the left side of the image is still not OK. I tried to adjust my previous SB, because it looked like the rear glass element was a bit skewed. It´s very loose if you don´t thighten the screw properly. Anyway, the adjustment didn´t pay. The left side was still too soft, while the right side was fine.

If only I had an optics free adapter for my Sigma, just to make sure that the lens is flawless.

UPDATE: A grid pattern should work fine to clearify the problem, although the effects gets more obvious if the focus is set to infinity. The 18mm image shows some reflections, as I had to use my screen as a brick wall replacement... The vignetting isn´t that strong in reality, I just wanted to emphasize it, maybe it tells you something I don´t know.




And here is what I see if I take a look at the BMPCC monitor. The focus peaking proves that the center seems to be shifted!? The camera was very well aligned to the monitor, yet the sharp center isn´t centered. This is exactly what I noticed with my fist speed booster and my first Sigma 18-35 too.

A couple of points: -

Firstly I am impressed with your shot of the tower etc taken at f2.5. It is sharper than anything I have managed with my set-up.

I am also interested that the lens elements in your speed booster become very loose when the locking screw is undone. This is what I was worrying about in my first post. I do a bit of lathe work including screw cutting. If I had made a thread that was as sloppy as that I would start again. I do not know how sensitive the alignment of the lens elements is but with that degree of looseness they must be pushed to one side when the lock screw is tightened.

I do not know how sensitive the alignment of the lens elements is but with that degree of looseness they must be pushed to one side when the lock screw is tightened.

This is exactly what I am suspecting too! If I tighten the screw, the rear element of the SB seems to be lifted on one side. Maybe this is the reason why the left side is always softer, because the screw sits on the right side of the SB?

I have sent an eMail to Metabones describing these observations. I will let you know if I get a reply.

I have sent an eMail to Metabones describing these observations. I will let you know if I get a reply.

Thanks a lot!

Maybe there are some BMPCC owners here who can share some pictures that were taken with a speed booster and a Sigma 18-35 at F1.8. Maybe all speed boosters behave likewise when shooting wide open?
In my case, I can either get a sharp center and out of focus edge regions or sharp edge regions and an out of focus center... Additionally, the focussed center isn´t really centered, as you can see above.

Oh man, i think i'm getting the same issue with my BMCC and my Zeiss zf 85mm:
https://www.dropbox.com/s/auo3q2jtwgb3n ... 086700.tif

Sharp on the right side and soft on the left...

Oh man, i think i'm getting the same issue with my BMCC and my Zeiss zf 85mm:
https://www.dropbox.com/s/auo3q2jtwgb3n ... 086700.tif

Sharp on the right side and soft on the left...

Geez! Looks familiar to me...
Seems like the speed booster is the evildoer here! I bet it has something to do with that unfavourable concept of locking the wiggly part of the speed booster with a tiny screw. The screw applies pressure onto the rear part of the SB and lifts it a tiny bit.

Please take your SB and look at it from the bottom side (with the four holes).
Does the adjustable part with the small screw look like it was perfectly aligned?
If I eye up my SB, I notice that the rear lens is somewhat tilted, but I don´t know if it´s the whole lens or just the ring that holds it in place.

Can anyone else please make some tests with the BMPCC speed booster and a fast lens? Maybe this is a common but overlooked issue...

EDIT: @ João Gomes: Sorry, I didn´t ask you if you were even using a SB for this particular shot...

Please take your SB and look at it from the bottom side (with the four holes).
Does the adjustable part with the small screw look like it was perfectly aligned?
If I eye up my SB, I notice that the rear lens is somewhat tilted, but I don´t know if it´s the whole lens or just the ring that holds it in place.

Mine looks absolutely normal. I've just played with the screw and positioning of the glass but didn't notice any changes.

On my case, i have to take into account that the Zeiss 85 f1.5 is known to be quite soft around the edges.

For now i just solved it using an inverted power mask with sharpness applied but would love to hear if more people have noticed this issue.

Sharp on the right side and soft on the left...

Which aperture (or number on the speed booster) did you choose for this shot?

Sharp on the right side and soft on the left...

Which aperture (or number on the speed booster) did you choose for this shot?

I was at f.4.

Sharp on the right side and soft on the left...

Which aperture (or number on the speed booster) did you choose for this shot?

I was at f.4.

Could you please do another test and shoot something outside with your lens wide open and the focus set to infinity? It would be interesting to see if the left side of your image becomes even softer while the right side stays rather sharp.

Thanks!

Could you please do another test and shoot something outside with your lens wide open and the focus set to infinity? It would be interesting to see if the left side of your image becomes even softer while the right side stays rather sharp.

Thanks!

It's tough to shoot with the lens wide open since it's a f1.5. I´m shooting trough a Tiffen 2.1 and still i can only go as open as f4. I'll try to make the time to shoot later in the day but i've been very busy.

Cheers.

I have had 3 replies from support@metabones.com
This one makes the most sense and seems to admit to a very loose screw thread on the lens element block: -

HI, Alastair,

It can’t make sure that you setting have problem….
It need to base on your Lens and aperture data too…..

Anyway, i will ask to our engineer for this case,
you also setting the infinity again……

You can add some paper type inside the speed booster’s thread first,
and then install a glass again, then screw-in the Lock screw with plastic ring.

Thank you!

Could you please do another test and shoot something outside with your lens wide open and the focus set to infinity? It would be interesting to see if the left side of your image becomes even softer while the right side stays rather sharp.

Thanks!

It's tough to shoot with the lens wide open since it's a f1.5. I´m shooting trough a Tiffen 2.1 and still i can only go as open as f4. I'll try to make the time to shoot later in the day but i've been very busy.

Cheers.

I see, thank you for your efforts!

I have had 3 replies from support@metabones.com
This one makes the most sense and seems to admit to a very loose screw thread on the lens element block: -

HI, Alastair,

It can’t make sure that you setting have problem….
It need to base on your Lens and aperture data too…..

Anyway, i will ask to our engineer for this case,
you also setting the infinity again……

You can add some paper type inside the speed booster’s thread first,
and then install a glass again, then screw-in the Lock screw with plastic ring.

Thank you!

Thank you! I tried to adjust the SB, but the focus problem still exists. If only there was someone with a BMPCC + SB and a Sigma 18-35 who could test this combination under similar circumstances...

I have had 3 replies from support@metabones.com
This one makes the most sense and seems to admit to a very loose screw thread on the lens element block: -

HI, Alastair,

It can’t make sure that you setting have problem….
It need to base on your Lens and aperture data too…..

Anyway, i will ask to our engineer for this case,
you also setting the infinity again……

You can add some paper type inside the speed booster’s thread first,
and then install a glass again, then screw-in the Lock screw with plastic ring.

Thank you!

Thank you! I tried to adjust the SB, but the focus problem still exists. If only there was someone with a BMPCC + SB and a Sigma 18-35 who could test this combination under similar circumstances...

I have the combo and will try to test it over the weekend.

I have had 3 replies from support@metabones.com
This one makes the most sense and seems to admit to a very loose screw thread on the lens element block: -

HI, Alastair,

It can’t make sure that you setting have problem….
It need to base on your Lens and aperture data too…..

Anyway, i will ask to our engineer for this case,
you also setting the infinity again……

You can add some paper type inside the speed booster’s thread first,
and then install a glass again, then screw-in the Lock screw with plastic ring.

Thank you!

Thank you! I tried to adjust the SB, but the focus problem still exists. If only there was someone with a BMPCC + SB and a Sigma 18-35 who could test this combination under similar circumstances...

I have the combo and will try to test it over the weekend.

That would be great, thank you!

I have not noticed this problem shooting charts or scenery with my MFT SpeedBooster and Sigma 18-35 on the Pocket camera.

Sir_danish, I just noticed you never stated which SB you have. Is it the Pocket SB? I suspect so, given the slight vignetting in the corners on the grid picture.

A couple of things to be aware of: the Pocket SB is made so the entire image circle of an APS lens is used. So imperfections in the corners that all lenses have will not be cropped out as they are with other SB's and plain adapters.

You are changing the f-stop and decreasing dof when shooting wide open.

With the scenery shots at "infinity" above, the objects at the left and right are at different distances.

I haven't seen anything in the examples above that screams "defect."

It´s the Pocket SB, yes. The softer left side can´t be the result of an imperfect Sigma 18-35, as this is my second lens of this kind. I´ve tried both lenses with the same SB and the same camera. In both cases I couldn´t get the left and the right side in focus simultaneously, as if the focal plane was skewed or something. This has nothing to do with different distances of objects, because I noticed the out of focus left side in almost all of my footage that was shot wide open. It´s unlikely that two Sigma 18-35 have exactly the same "defect", namely a badly cut or misaligned lens. By the way, I´ve tried two Speed Boosters and two Sigma 18-35.

The only thing I didn´t change yet is the camera itself. Maybe the lens mount isn´t perfectly aligned, who knows. The thing that puzzles me though is the image posted by João Gomes:
https://www.dropbox.com/s/auo3q2jtwgb3n ... 086700.tif

It´s not that obvious, but if you look closely, the very left part of the image is softer than the right side and it doesn´t look like this is due to different distances of the buildings.
I also don´t believe that this has something to do with the general softness of the lens. I´ve never owned a lens that was unevenly soft, that´s why I suspect the SB to be the problem.

I don´t know if I´m wrong or right, until someone with exactly the same setup shoots something outside with the lens wide open and set to infinity, like I did many times in low light situations.

I should point out that i'm using my BMCC with the Blackmagic specific speedbooster.

I should point out that i'm using my BMCC with the Blackmagic specific speedbooster.

You said that your lens is known to be rather soft in the corners. I´ve looked at your image closely and to me, it didn´t look like the softness on the left side was a result of some optical weaknesses of your lens.
The center is very sharp, the right side is too. I wonder why the buildings and the bridge are softer on the left side.

One could think that this has something to do with the distance of certain objects on the left side, but there are buildings in the center of the image that seem to be even further away from the camera than the ones on the left side, yet they are perfectly sharp! The same applies to the right-hand side, where everything is sharp and crispy.

If only I had another BMPCC with a different lens to test. Maybe you find the time to make a test shot in the evening, when there is less light so you can shoot wide open. I would be glad to see some footage.

Thanks!

It seems plausible, since wide angles are more critical in flange distance than anything. Even the tiniest tilt in the lens group of the SB can cause such a problem.

It seems plausible, since wide angles are more critical in flange distance than anything. Even the tiniest tilt in the lens group of the SB can cause such a problem.

Thats exactly why I think that the SB is the problem. It would be very interesting to see if all BMPCC or BMCC Speed Boosters behave the same, as this is my second SB with the same characteristic. Maybe the locking screw on the rear lens causes a slight tilt! If this is the case, I´m going to contact Metabones and ask for an improvement.

I was wondering if this was ever resolved? I seemed to have the same problem with my pocket camera, SB and the Sigma. It is soft on the left.
I have tested both the Sigma and a Nikkor Prime and both showed the same problem.
I also borrowed a Lumix prime/MFT and it shows no such problem (of course it is generally must softer).

Hey guys

been having a similar issue for a while now and there seems to be no fix. What you're describing as soft, can you rack focus and ever get the side in focus?

I'm having an issue where I can either get the center OR the sides sharp, but never both at the same time unless I stop down to F11 - with any lens. It's pretty bad. I'v sent my bmpcc speedbooster in for repair, they sent it back and the problem persisted. They asked me to ship it back and offered to replace the unit. It arrived this morning and still, the problem continues.

I'm starting to think it's a fault in the design. Perhaps the Nikon mount SB for bmpcc isn't professional grade.

I have the same issue with my Sigma 18-35 and the Pocket-SB, left hand side is soft, more so when I'm wide open, the focal plane on the SB is definitely out somewhere, it's not the lens as the Sigma is perfect on my Canon 600D, I can't see an easy fix for this as it could be many issue with an six element system that the SB uses.

The unfortunate part is that it does not seem, so far, that metabones wants to address that there may be a inherent flaw in the design but instead offers to replace or fix a unit with another unit that has the exact same issue. Would love to help them get the product to where it needs to be but haven't spoken to the right people yet.

Well ... a lot of people here suggest speedbooster and the 18-35 as the optimal combination for the pocket. Rather than native MFT lenses.

Either they dont have this problem or they don't see it.
Let's me think about advices from the internet ...

Just checked with my bmPcc speedbooster and sigma 18-35: i can't see evidence of a shifted focal plane in my combination; i slowly altered focus through and inspected the center and sides of the image, and found the sides to become focussed simultaneously, while the image center was slightly defocussed then. The test was performed at about f/4.

The Sigma (and most photo lenses) are not "flat field" copy lenses, and therefore do not have a "flat" field of focus, rather, the focus point shifts slightly at the edges, so if edge is sharp, center de-focuses, and vise versa. The speed booster might be emphasing this shift, making it more noticeable. If you need a flat focus field, you need to use a "copy" lens, designed for shooting flat material. The wider the lens, the more field of curvature it will have

The Sigma (and most photo lenses) are not "flat field" copy lenses...

Sure, that's not the point here. Center and sides will not be perfectly focussed at the same time, that's to be expected, and that's what i found for my lens/booster combo. However both sides of an image should be in focus at the same time (as they are in my test), whereas the thread starter found that the left side of the image was blurry while the right side wasn't, and that should not happen.

I'd say that his speedbooster isn't collimated perfectly.

I´ve tried two different Speed Boosters and both showed exactly the same problem, just like in PaPa´s case. Don´t you think it could be a series fault?

Maybe your cameras mount is damaged?

Maybe your cameras mount is damaged?

Christian Horne seems to have the same problem, Thomas Nerling and two other guys at eoshd.com have noticed the "shifted focal plane" too. Maybe we all have slightly misaligned camera mounts? It seems plausible, because I´ve tried two Speed Boosters and two Sigma 18-35 with exactly the same results on my BMPCC.