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Exploring Issues with Infinity Focus and the Blackmagic Cinema Camera

02.13.13 @ 5:18PM Tags : , , , ,

Some conversations have been appearing recently talking about infinity focus issues with specific lenses and the Blackmagic Cinema Camera. One of the biggest offenders so far has been the Tokina 11-16mm f/2.8 lens, which is one of the few faster wide options for the EF mount BMCC. Unfortunately, it seems that many people have replicated these issues, and a recent video posted online shows just how bad the situation can be.

Dan Chung at DSLR News Shooter recently posted this video from Raitank showing the problem:

They have also posted an additional video:

Here’s what Dan said about the situation:

It seems that most genuine Canon EOS lenses are working as they should because they tend to focus slightly past infinity. The main exception seems to be the recently released 40mm f2.8 STM lens which some users claim gets nowhere near infinity.

Other users are saying that older legacy lenses and even manual focus Zeiss ZE lenses are also affected. On Blackmagic’s own forums user Phillip Mortimer has posted several examples of problems achieving infinity focus with vintage glass and adapters. You can download them here for the first camera he tested, and here for a replacement that was sent to him by Blackmagic. It is clear that both cameras exhibit the issue.

I have run some tests with my own BMCC and several lenses and it appears that I too have the same issue. Lenses that achieve infinity focus on a Canon 6D or C300 do not do so on my BMCC. So far I have tested the Canon 40mm f2.8 STE, Zeiss ZE 18mm and 85mm lenses, along with several Leica R lenses adapted using the excellent Leitax R to EOS adapters. To a greater or lesser extent they fail to achieve infinity with my camera.

In my testing with the camera, I do not remember this being a serious problem, but I do recall that at one point infinity didn’t seem as sharp as I thought it should have been — but I don’t believe that was with the Tokina. Each lens was a Nikon mount with a Canon to Nikon adapter, and that included the Nikon version of the Tokina 11-16mm. It’s unclear at the moment what is causing this issue. Cheaper SLR lenses are not made to very strict tolerances, so these sorts of issues crop up all the time. Why some lenses do not have any issues on the Canon cameras but cannot reach infinity on the BMCC is very strange indeed.

Blackmagic is investigating the issue at the moment, so we should have some sort of response or solution in the near future, but it has been stated a number of times by the company that the flange distance of 44mm is exactly the same as Canon’s own specification for the EF mount. The issue is that there is no way to adjust back focus with any of these lenses without taking them apart, and the BMCC has no way to adjust back focus within its mount. Since none of them are in the hands of regular users at this time, it’s not clear if the MFT mount version would experience the same infinity focus issues with Micro 4/3 lenses or other lenses adapted to that mount.

We’ll update you once Blackmagic responds. In the meantime you can head on over to the forum and read more about the experiences of other users.

Link: Flange distance issue — Blackmagic Forum

[via DSLR News Shooter]

Disclosure: Blackmagic Design is a NoFilmSchool advertiser


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Description image 38 COMMENTS

  • This is the reason why they should just sell the MFT version..with electronic contacts..rather than the EF.

    • Jorge Cayon on 02.13.13 @ 6:33PM

      This could very well happen to a MFT version as well. If the lenses work on other cameras, specifically Canon models than it isn’t a lens issue. Firmware updates can most likely fix this.

      • Clayton Arnall on 02.13.13 @ 6:39PM

        hmmm, how can firmware fix focus? Seems to me the mount is too long, making the lens slightly macro. Much like if you threw an extension tube between a camera and lens. The infinity point gets shorter.

        • Jorge Cayon on 02.13.13 @ 7:26PM

          They can try and trick the lens if all we’re talking about is infinity. Honestly if I had the EF model right now I would sell it for a small profit. If they truly wanted this to be a “Cinema” camera they would not have chosen the mount for a stills camera on their first release. MFT or PL would’ve made a better choice, at least a filmmaking goes.

          • Pretty sure this isn’t talking about AF. Particularly since according to the article, some manual lenses are affected as well. I don’t think the BMCC even has AF in the current firmware version.

  • I’ve found it a pain in the ass so far trying to get some landscape shots, I don’t know how they are going to fix the problem, is it even fixable?

  • Wow, problem after problem,with massive delays and now more serious problems. You wouldn’t be a small camera manufacturer for quids … Or jump the gun to buy one for that matter :-(

  • Sigma 10-20 seems better

  • The sensor issue is understandable…but there is little excuse for this. BM could and should have gone the extra step in pre-production and purchase/test a cross section of lenses to confirm the suitability of the flange distance selected. This would have had two important benefits:

    1) They would know if all tested lenses (particularly wide angles) would focus to infinity. Were they not aware of this issue with other cameras (Red) in the recent past?

    2) They could provide a DATA BASE of guaranteed compatible lenses (obviously not all…just the most popular and likely to be used) for Infinity Focus AND viewfinder aperture readout.

    As it is the loyal, trusting customers have been hit by a double wammy…unreasonable delivery delay AND focus issues.

    • The old handcraftsman’s rule: measure two times, cut one time.
      Although I’m not interested in this camera personally I really want Blackmagic to make it a success story.

  • 2.3x crop is painful. Very few fast zoom choices on the wide end. I have the Tokina 11-16. It’s OK, nothing more. It’s ƒ2.8, most in this range are ƒ3.5, ƒ4, or the dreadful ƒ3.5-4.5. Makes ya wanna get the C100? At 1.6x crop don’t have to suffer with this Tokina.

    • Nah, just makes me wanna get a BMCC MFT version with a Metabones Speed Booster.

      • Kenneth Merrill on 02.14.13 @ 3:10AM

        Pretty sure the Speed Booster doesn’t come in a MFT version yet. Oh wait, the BMCC doesn’t either.

        • No, but they will, and I don’t need to buy the camera today, so it doesn’t bother me.
          Specially considering Canon won’t be coming up with anything nearly as comparable to the BMCC+Speed Booster anytime soon.

    • Agreed. The Tokina 11-16mm, which is super wide even on APS-C, looks to be about 25mm in focal length, on the BMCC 2.5K. The combination of small sensor and EF mount is a little bit awkward. It’s not prohibitive, but I shoot a lot of landscapes. I didn’t want to buy an 8-16mm Sigma that I would ONLY use on the BMCC 2.5K.

      I’ve been used to RAW landscape images from a s35, full-frame, and that smaller sensor has a different “look” than full-frame..

      My opinion is that most cameras are going to look fine for tight (interview) shots, it’s really the wide shots where you’ll see the difference in image quality, and I wasn’t getting the end result I wanted. By this serpentine logic, I found the BMCC 2.5k to be the wrong camera for a nature/landscape filmmaker (I returned my camera and got a Nikon D600 instead, and I’ve been happy with the swap — I do a lot of time-lapse still photography also)

  • I have had a Nikon mount Tokina 11-16 on my GH2 for years and it’s always focused slightly past infinity. I just got used to focussing a small twist back. I would be very surprised if BM measured the lens mount wrong…

  • My take: they didn’t measure the lens mount wrong. But they measured it with their old sensor filters and old bonding methods (the ones that gave horrible IQ issues and caused the delays). The new ones must add a bit more diffraction, and they didn’t take that into account.

    No easy solution if that’s the case…

    • And BTW, if that’s so, they’d have to redesign both the canon mount and the MFT mount.

      • No, because there are no such different mount versions in MFT, so they probably got that one right (hopefully) and the rest is up to the quality of third party adapters going into almost any lens available to man. I use the Fotodiox brand and they have been an absolute success for me and my GH2.

        • The problem with the canon mount is that it sits maybe a quarter of a mm too far from the sensor. If the MFT mount sits a quarter of a mm too far from the sensor, it will have exactly the same problem.

          It all depends on whether they made the MFT measurements before or after changing the filters in front of the sensor, and how much it takes them to solve the issue if it is there.

  • OR…they measured the distance BEFORE getting rid of the optical low pass filter.

  • This is a pity. I was planning to purchase a BMCC once they start shipping properly, but if there is a focus issue and/or more production delays then I will look elsewhere (maybe the c100, though my friends who work on more serious productions don’t like that line). And based on that thread someone linked, there definitely seems to be a focus issue if it doesnt focus to infinity with zeiss glass either.

  • I had the chance to test this camera yesterday as a 1st AC and I found this problem. I was using a manual focus ZEIS ZE 35mm camera, and it happened in every exposure we used.

  • *Lens, not camera.

  • Nobody has ever screwed up a new camera introduction as badly as Blackmagic has screwed up this one. It’s amazing to behold.

  • How long will I have to wait for 2.5/or 4k raw at a reasonable price and with no problems? .. I wish Canon or someone else is able to release such a package …Although perhaps there are too big for such a move..from the other hand side I m intrigued with BMCC but the company is still young and learn.

    I look forward to see how they can fix this .. perhaps the distance to the sensor is greater than initially thought .. or during the production process someone typed an extra mm to the production line and the adapters come with offset ..

    Funny enough that suits really well the rest of video camera world!


  • My EF 11-16 can’t hit infinity on my 60D… I’m gonna go with the lens being at least PARTLY to blame.

  • You get the same issue on a RED Scarlet/Epic, but you can adjust the backfocus of the REDs.

  • I remember in days of sony z5 and z7 there is a similar problem, focus can not be achieved infinity or even close subject focus, and the lens was wide angle, the camera needs to know the focal length of the lens, and fixed with a tool inside the camera called (flange corrector), in BMCC case, maybe this have something to do with focal length especially wide angle lenses, a distant between camera and sensor maybe needs to re adjusted, if that the case with BMCC I wonder how BM will fix it? maybe an adapter between lens and sensor?

    • Unlikely since the required adapter thickness will be less than a mm, and I doubt there’s a way to build an EF-EF adapter so thin.

  • Sounds like you might need to send that lens in to the shop, you shouldn’t be experiencing that issue on a Canon camera.

  • I can confirm this issue on the Sony FS700 as well with a vinatage 135/2.8 Zeiss Contax Prime.

  • Daniel Mimura on 02.21.13 @ 7:39AM

    Wow…I’m so glad I didn’t go with this camera. They want to call it a “cinema” camera, but it doesn’t have a way to adjust the backfocus? That’s one of many reasons it sounds more like a D-SLR to me than a movie camera.

    It’s one thing after another. I’m so glad I couldn’t wait and wound up getting a BTR1 MX instead. An end of life camera has most of the major quirks ironed out by this point, versus the host of problems a new camera introduces.

  • No problems that I’ve seen with any of my lenses on my BMCC, seems to be a very slight tolerance/build quality problem mostly with the Tokina. Here’s the same lens with a problem on a Red body:

    Someone did figure out that you could fix the problem if you take a shim out of the lens, but obviously that’s not for everyone.