RED 18-50mm holding focus?

[Aiden K.]

When I zoom in to 50mm and focus, is it supposed to hold that focus when I pull out to 18mm? because when I do, the focus is off. The numbers in the RED LCD stay the same, but the image is NOT in focus when pulled back to 18mm. I have to refocus a little further out (or closer in).

 

[Steve Sherrick]

Is your backfocus set correctly?

 

[Brook Willard]

That's a lens issue, not a flange focal depth issue. The lens needs service.

 

[Brent Carter]

When I zoom in to 50mm and focus, is it supposed to hold that focus when I pull out to 18mm? because when I do, the focus is off. The numbers in the RED LCD stay the same, but the image is NOT in focus when pulled back to 18mm. I have to refocus a little further out (or closer in).

Shoot me an email at brent - at -red - dot - com and I can help you out with troubleshooting and getting the lens in for eval, as needed.

BC

 

[Aiden K.]

Thanks for the help guys. I was talking with Chad last year about a second problem with the lens that when I zoom in or out, the image shifts on the sensor. I just never had time to send it in, but now that there are 2 things wrong with the lens (which probably always was wrong with it) I'll make time to get it sent in.

 

[Peter Repich]

That's a lens issue, not a flange focal depth issue. The lens needs service.

If the Flange Focal Distance (FFD) or Back Focus on the lens is off (lens terminology), the zoom lenses will not track (hold focus while zooming). Both have to be set to the proper 52 mm specification. The lenses need to be set via a profettional collimator (Gecko or Chroziel - very accurate instruments) and the digital cameras need to be set via a digital FFD device.

Peter Repich

peterr@uniQoptics.com