Today Blackmagic Design announced a fix for the Blackmagic Cinema Camera for a flange distance issue which could cause back-focus / infinity focus issues especially with certain wide angle EF lenses such as the popular Tokina 11-16mm zoom.
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."