Blackmagic Pocket Cinema Camera 4k back focusing issue

I have a Blackmagic Pocket Cinema Camera 4k and Metabone speedbooster ultra 0.7X and with canon 24-105mm lens.
I have problem back-focusing using BMPCC 4k, when I set my focus to an subject, without changing the our distance, I only change the zoom on the lens, but for some reason I lost focus during the process, meaning the focus point at 24mm is different at 105mm. Is there problem with the compatibility or other issue

The lens loses focus when you zoom? This is not according to my knowledge a back focus problem. This is a normal issue with zooms that are not parfocal. I have never used a Canon L 24-105 that WAS parfocal. The issue may be exacerbated by the adapter since it might need micro adjustments to get the focal plane to be exactly where it should be on the sensor. You will see in many documentaries or faux documentaries (The Office style) where this problem actually aides in the aesthetic.

True zooms that are parfocal tend to cost much more than the common varifocal zooms that are on the market, such as the 24-105 F4 L.

Generally, it is a good idea to use varifocal zooms more like variable primes and not to use them like industry parfocal zooms, such as those glued to studio broadcast cameras.

I have a Blackmagic Pocket Cinema Camera 4k and Metabone speedbooster ultra 0.7X and with canon 24-105mm lens.
I have problem back-focusing using BMPCC 4k, when I set my focus to an subject, without changing the our distance, I only change the zoom on the lens, but for some reason I lost focus during the process, meaning the focus point at 24mm is different at 105mm. Is there problem with the compatibility or other issue

Additionally, cameras normally do not have a back focus adjustment. Some cameras with certain mounts, like PL mounts, can be shimmed to adjust inf. Focus. Back focus adjustments are found on Broadcast parfocal Zooms and some cine zooms. Still camera zooms are not real zoom lenses, but more of a variable focal length lens, and are not parfocal. The MFT mount in the Pocket 4/6K can not be shimmed, due to the lens contacts. Same goes for BMDs fixed EF Mount Cameras, like the Pocket 6K.

That said, Nikon’s new S Zooms for their Z cameras are parfocal on a Z6/7 Camera. Some Canon cameras can adjust the focus on the fly when zooming, to give the appearance the lens is parfocal, but this only works on the higher end Canon camera bodies.
Cheers

You can adjust back focus with your Speed Booster, go check out how to adjust the back focus on your Speed Booster. My Sigma zoom are working great with this adjustment.

On the other hand, I'm having problem with the back focus on the M. Zuiko zoom.

Does anyone know if there's shim sold for PCC4K?

metabones infinity adjustment:

https://www.metabones.com/article/of/in ... oster-only