Nikon F3 focus adjust

[De_Corday]

Hey all. One of my F3 bodies is having a focusing issue where, at infinity, the split image isn't quite aligned... the upper half is still just a hair to the left of the lower half. This is consistent across lenses, and fairly minor (I've never noticed problems with it on film, for example) but I seem to remember reading about adjusting the mirror in the mirror box to deal with this very issue...
I know there's an adjustment screw off to the lower right-hand side of the mirror. Does anyone know the proper procedure for this adjustment?

 

[presspass]

I, too, would be interested in learning how this repair can be done and how I can tell if it is successful. Any help appreciated.

 

[Dwig]

BEFORE you do anything keep in mind that having the image focus "properly" in the VF doesn't mean that it will be focused properly on film.

The focusing problem could be the result of:

• The focusing screen no being seated properly
• The mirror being out of alignment
• The mirror box being distorted moving the lens mount out of position

You need to find out what is the cause of the error before you look for a fix.

 

[_tom]

In order to check if the infinity focus is correct aligned, you´ll need a special reference 50/1.8 infintiy lense #J18010 (according to the service manual) and a collimator #J19001.
Throughout devices that not everyone necessarily has at home. Otherwsie take a look here: http://www.rangefinderforum.com/forums/showthread.php?t=117411
Greetings...

 

[jim_jm]

Have you tried checking the focusing screen? Maybe swap it out with the screen from one of your other F3 bodies to see if the problem is still there. If it was a mirror alignment issue I'd think the problem would be apparent across the entire field of view, not just the split-image. Try focusing on something flat like a brick wall about 10-15 feet away. If the mirror is out of alignment, I would think you'd see a large part of the view was OOF.

I'd eliminate any other possibility before mucking with the mirror alignment.

 

[De_Corday]

Just checked--it's true across focusing screens... same problem with an identical K screen at infinity focus.

I've shot many rolls of film with this camera and it's never an issue I notice on film... whether that's because the variation is so small it'd only be obvious shooting wide open or because the film is in focus while the VF is not...

I have a parts F3... Maybe I'll check the mounting flange on this one against the parts-body and see if there's a difference in trueness?

 

[De_Corday]

swapped mounting flanges from another F3, problem seems more pronounced, even though the original mounting flange seemed a bit warped... thinking maybe some previous owner toyed with the mirror alignment to compensate for the warped flange?

Also, the same lens on the parts F3 with a different focusing screen and the warped flange recreates the problem... might assume its the flange and adjust the mirror to match?

at least I have one good F3 🙂