Backfocus way off and not correctible

[Bruce Byker James]

Hi.

I'm having an odd backfocus problem:

As it is now, a 40mm Zeiss prime at 5 feet must be turned all the way to infinity to get the image in focus, so I lined the camera up with a focus chart 5 feet away and loosened the backfocus screws. The backfocus setting was turned almost all the way to the right, putting the lens mount almost as close as it could get to the sensor. When I turn the backfocus ring counter-clockwise, it pulls the mount away from the sensor, adjusting the focus closer. This is not the direction I need to adjust the backfocus and there is no more adjustment left in the other direction.

Something appears to be off and I have no idea what it could be. This camera is used by students, so there's no telling what could have happened and I feel like I'm on a bit of a detective mission here.

By the way, I did try another lens just to make sure it wasn't a lens problem and got the same results.

Any ideas?

Thanks,

- Bruce

 

[Jacek Zakowicz]

It looks like the adjuster skipped thread because it was loosened too much. You can tell that AFAIK by measuring the gap between the rotating ring and camera body.
It should be no more than 1mm in the extreme close setting(like you have when you can't turn clockwise any more).
You can try to loosen and push back (gently non hammers :wink5 but that rarely works.
Best to remove and reengage.
Based on the little info here I could be completely wrong BTW...

 

[Steve Sherrick]

The flange adjustment on Red One needs to be handled with care. It's possible that it was loosened too much and the internals have been messed up, not allowing you to get it back in alignment. Might need to be repaired. I would educate students on this process because it's not something you want to have happen too often.

 

[Bruce Byker James]

The gap between the rotating ring and the body was less than 1mm when I got it. Good point about educating students about backfocus. This hasn't been a part of the training so far.

I took off the PL mount and one of the wires that attaches to the mount is broken so I think someone must have done as you mention and loosened it too much. I'm going to put it back together and see if the problem is still there.

Thanks for the responses!

- Bruce

 

[Douglas Underdahl]

Right, it sounds like the mount was loosened too far and the exterior plate has come off the studs. I saw this once. I loosened the two 4mm screws on the adjustable collar and turned it so that the outer plate unscrewed, then re-indexed it on the studs so it wouldn't rotate (it shouldn't rotate, the studs stop it from doing this). Then I reset it with my shop standard lens. It may be that the outer plate came off the stud on your camera because it was loosened too far.

 

[Bruce Byker James]

That appears to be exactly what happened. As I attempted to line everything up I noticed that the mount was turning outside the studs, so I re-indexed it and put everything back together and all is well. Except for the lens info connection. Can anyone comment on how difficult it is to get to the point where you can re-attach the lens info wires? When re-indexing I noticed holes that line up with several larger torx screws. Is this the next step?

 

[Douglas Underdahl]

This video might help:

http://www.youtube.com/watch?v=IhmolBMtDzg

also watch the next one, which is part two.

You should be able to solder the disconnected wire back onto the little white connector if you are good at that sort of thing. If the wire is broken off inside the camera, I would get ready to send it to Red.

If you don't use PL lens data, then you could simply cover the connector and the end of the unattached wire with tape or heat shrink and carefully pack it back into the recess, leaving it disconnected.

 

[Bruce Byker James]

Thanks for the link. The wire is broken in the middle of its length and there's enough slack that I could just reconnect it and cover it with some heat shrink. This camera is destined for Stage 3, though, so I thought if it wasn't a big deal to get a little further into the camera and replace the entire wire harness I would go ahead and do it to avoid unnecessary charge and delay when it goes back to RED.

 

[Marcus Struzina]

I would be contacting Red about this one asap, as a short in these wires has apparently caused havoc in the past. I'd be guessing that opening the camera further would void the trade in deal too, so exercise caution.

 

[ericyoung]

Thanks for the link. The wire is broken in the middle of its length and there's enough slack that I could just reconnect it and cover it with some heat shrink. This camera is destined for Stage 3, though, so I thought if it wasn't a big deal to get a little further into the camera and replace the entire wire harness I would go ahead and do it to avoid unnecessary charge and delay when it goes back to RED.

I wouldn't mess with that wire harness without talking to Red. And be very careful to avoid pinching any of the wires when reassembling the mount, or letting the loose one potentially short against anything (tape over it). This can potentially cause an expensive repair to be needed, especially if it's going back for Stage 3. Explain as you have above that students have been at it!

 

[Robert Knoll]

You have nothing to lose in repairing yourself if you are confident and have the skill. Just be careful. If it has to go into Red after your attempt so be it. Just be gentle and have a good eye. A broken wire is no big deal to repair correctly.