Cooke 20-100 back focus adjustment

[Nacho Guzman]

Hello everyone

Pretty impossible to find a manual of this lens anywhere, before sending it to a technician, I was wondering if anyone know if is possible to manually adjust the back focus so the lens stays sharp all the way.

 

Lens came back from a job as is now incapable of doing it, so wondering what option could be.

 

So far has proven to be a tough one to be able to answer.

 

Thanks everyone in advance

Nacho

 

[Dom Jaeger]

Generally the back-focus on zooms like this doesn’t just go out, so if you’re finding the zoom no longer holds focus after a job, when it did before, chances are something has happened that needs a lens tech to diagnose.

Cine zooms like this are among the most complex lenses you can find, definitely not in the realm of DIY repair.

The only thing I would suggest before sending it to a pro, is to check whether the Intermediate mount at the back is properly seated and secured with the lock ring. And make sure that the camera you’re checking it on is OK in terms of flange depth (ie do other zooms hold focus?)