By site editor Dan Chung:
Last week Blackmagic Design acknowledged what some of its customers already knew. Certain stills lenses were not able to correctly focus to infinity when mounted on the EOS version of the Blackmagic cinema camera. The main problem lens appears to be Tokina’s 11-16mm f2.8 – which multiple users have found to have issues. My own BMCC exhibited this problem with multiple lenses that I tried. The problem also existed with other stills lenses that I own.
After an investigation by Blackmagic’s Kristian Lam this is what he had to say on the company’s user forum:
I want to give you an update about this issue.
The cameras are all shimmed and calibrated to 44mm as per the reported focal flange depth of EF mount. I use the term “reported” as Canon does not publish the specifications officially so the exact expected tolerances are not known.
When checked against a collimated cine lens, we expect the Blackmagic Cinema Camera to get accurate focus according to the witness marks on the lens. For example, at focus chart placed 6 ft from the camera sensor plane will be in focus when the witness mark on the lens is at 6 ft.
When I tried the same collimated lens on some 5Ds, 7Ds and even a C300, the witness marks fall short of the expected distance which indicates to me that there’s some fair amount of tolerances built into the Canon cameras to cater for still lenses where the tolerances are not as critical as cine lenses.
To address this, we need to put in the same allowances. We have tested this with some of the cameras from customers reporting this and it works.
If you think you’re encountering this issue, please contact your local Blackmagic Design support office and we’ll sort you out.
So what this means in practice is that owners who experience problems need to send their cameras to Blackmagic for re-calibration. It is not a full recall as not every user will encounter these issues. New cameras will ship with the new calibration that is better suited to stills lenses like the Tokina.
If you think you have this issue then I would advise you to first check to see if your particular lenses are good copies. If possible go into a friendly shop or rental house and try similar lenses. If the problem persists I would then contact Blackmagic customer support.
I have been lucky to be one of the first to have the calibration done on my BMCC and am happy to report that initial testing shows that it now focuses to infinity using myas well as other lenses like my and adapted Leica R lenses.
It is good to see Blackmagic responding to this issue and I look forward to giving the camera a proper workout in the near future.