Film-Tech Forum ARCHIVE: Flat Lens is going blurry

This is topic Flat Lens is going blurry in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Craig Kocher (Member # 2432) on 07-12-2004, 04:42 PM:

hello all, may be a stupid question, but we cant seem to figure this one out, hell, even our tech doesnt know whats wrong. It seems that during the first show ( usually around 10am ) the Flat Lens on one of my Christies is going immediately blurry. I can fix it obviously by adjusting it, but then the weird part is, it does this again during the second show, but corrects itself in a few seconds and then I have no problems for the rest of the day, Untill the next morning that is, when the process repeats.

Anyone experience this before? Any Suggestions?

Thanks

Craig

Posted by Wolff King Morrow (Member # 2226) on 07-12-2004, 05:09 PM:

That is strange. Could it be a thick splice knocking the focus out at the same spot in the trailers? I've seen this happen before. Or maybe some sort of heat expansion in the lense?

Posted by John Pytlak (Member # 331) on 07-12-2004, 05:23 PM:

Perhaps an element is loose, and changes position as the lens heats up? Or the lens mount/turret is loose and changes position with vibration?

Posted by Chris Hipp (Member # 1788) on 07-12-2004, 06:14 PM:

I will say it before Brad gets here to yell at you. Post the make and model of the lens to help everyone identify the problem.

I recently had a problem on an ISCO lens where the ring that holds the front element was loose and the focus would drift. Just tightened it up and fixed it.

Posted by Brad Miller (Member # 2) on 07-12-2004, 06:38 PM:

Craig,

Loosen the allen screws that hold your lens into the turret a little bit. Probably a half turn counter-clockwise should be enough. If they are tightened down too far, the Christie turret will exhibit this sort of focusing issue. Just make sure they aren't so loose that the lens can fall out.

If that doesn't work, post again with more detailed descriptions of how the focus behaves on screen.

Posted by Craig Kocher (Member # 2432) on 07-12-2004, 10:13 PM:

Thanks everyone for the advice. Brad, I'm in the Booth Wednesday Morning at 8am so I'll try it then and check back that night. Thanks again everyone, This place is so great, I'm trying to learn as much as possible and this place is definitly helping.

Craig

Posted by John Anastasio (Member # 607) on 07-13-2004, 07:04 PM:

I once had exactly this problem. It was caused by humidity getting into the lens. The lens was cold, then when the heat of the lamp hit it, the condensation formed on the inside lens element, sort of like taking a cold coke out of the fridge. After it stayed warm for a while, the humidity was driven from the lens and it cleared up.

Posted by Brad Miller (Member # 2) on 07-13-2004, 07:32 PM:

It can't be that. He reports that he can fix it by adjusting it, hence it's not a humidity issue.

Posted by Craig Kocher (Member # 2432) on 07-13-2004, 10:52 PM:

well, I'll know tomorrow morning, Our Tech is coming and were gonna get to the bottom of this...

Posted by John Anastasio (Member # 607) on 07-14-2004, 04:08 PM:

Agreed, Brad. I wasn't paying much attention... and I agree about the Christie lens screw on the turret. There's really nothing else there to move.