Exploring Issues with Infinity Focus and the Blackmagic Cinema Camera
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.
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.
[via DSLR News Shooter]
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