Canon lenses and Red Epic

[Reiner B]

I own a Canon 70 – 200 1:2,8 L lens and I use this with Red Epic and Canon mount. Unfortunately the focus is changing while zooming. This might be the flange focal distance. But I cannot find any way to correct it.
Any ideas?
Reiner

[Justin Chin]

That lens isn't a parfocal lens and thus doesn't hold focus through a zoom. Most Canon's are not parfocal, but a few are. I believe the 16-25 is.

[Curtis Stanton]

From page 7 of the Canon EF70-200 f2.8L IS II manual:

[Lauri Kettunen]

Justin, are you sure this lens is not parfocal. Have you seen Canon saying this?

Let's assume a lens is parfocal. In general there are two things which may still cause the focus to change while zooming. The first reason is the internal adjustment of the back focus within the lens. The second reason is the collimation of the camera.

To check these take e.g. the 16-35mm L f2.8 lens. That should hold the focus while zooming. If it doesn't, then adjust the collimation of the Epic. If you do this properly, and it still can't get the lens to hold focus, then it need to be sent to maintenance for internal adjustments.

[Josh Beadle]

That lens isn't a parfocal lens and thus doesn't hold focus through a zoom. Most Canon's are not parfocal, but a few are. I believe the 16-25 is.

Dude, this is a Technical Forum . . . not a teen chat room. Get your fact straight before posting

[N_Villers]

Dude, this is a Technical Forum . . . not a teen chat room. Get your fact straight before posting

?? Teen chat room ?? I also believe it is not parfocal and have focus shift with zooming. The manual clearly states this as posted above. So before sticking your foot in your mouth go check your own facts first!