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Dustyman
19-Feb-2015, 17:08
I recently picked up a late model 4x5 Gowlandflex, and I've been testing it out in the studio. After some needed adjustments to the rack and pinion to allow for smoother focusing action, I started to test the viewing lens ground glass against the ground glass of the film holder, on which the taking lens projects the image. I assume this is the best way to check focus accuracy.

Despite the fact that everything appears plumb (using a bubble level to gage everything), the lenses, both identical 180mm Nikkor-W in Copal 1 shutters, do not focus identically. I need to rack the focus nearly 1/4" more out to get the film plane ground glass to match the sharpness of the upper viewing ground glass.

I double checked to be sure all was parallel.
I assumed that if both lenses were identical then the issue must be either be...

A) a tilted front standard. It isn't.
B) a misaligned internal reflex mirror. It seems very secure in place.
C) a misaligned or loose viewing ground glass. That looks good too, with no play. It is flush to the top of the square frame atop of the camera.
D) an out-of-whack film back. But that appears flush to camera, and secure.
E) different lens boards or mounting hardware. Nope. Both exactly the same.

I ended up shimming the taking lens out, about 1/4", to allow both lenses to throw sharp images on both ground glasses.

So the question is, can identical lenses behave so differently? Many TLR cameras do use cheaper glass for viewing, and I would expect the difference might pop up in that scenario. But with the identical same lenses in the same shutters?

Anyone with similar experiences?

Randy Moe
19-Feb-2015, 18:09
I recently picked up a late model 4x5 Gowlandflex, and I've been testing it out in the studio. After some needed adjustments to the rack and pinion to allow for smoother focusing action, I started to test the viewing lens ground glass against the ground glass of the film holder, on which the taking lens projects the image. I assume this is the best way to check focus accuracy.

Despite the fact that everything appears plumb (using a bubble level to gage everything), the lenses, both identical 180mm Nikkor-W in Copal 1 shutters, do not focus identically. I need to rack the focus nearly 1/4" more out to get the film plane ground glass to match the sharpness of the upper viewing ground glass.

I double checked to be sure all was parallel.
I assumed that if both lenses were identical then the issue must be either be...

A) a tilted front standard. It isn't.
B) a misaligned internal reflex mirror. It seems very secure in place.
C) a misaligned or loose viewing ground glass. That looks good too, with no play. It is flush to the top of the square frame atop of the camera.
D) an out-of-whack film back. But that appears flush to camera, and secure.
E) different lens boards or mounting hardware. Nope. Both exactly the same.

I ended up shimming the taking lens out, about 1/4", to allow both lenses to throw sharp images on both ground glasses.

So the question is, can identical lenses behave so differently? Many TLR cameras do use cheaper glass for viewing, and I would expect the difference might pop up in that scenario. But with the identical same lenses in the same shutters?

Anyone with similar experiences?

I have the same camera but have not noticed this at all. But the way the viewing GG can be mounted or factory set is slightly sloppy, in my opinion and is adjustable by tapping new mounting holes. Mine is NOT FLUSH mounted. I would show pictures of mine, but I have mounted a metal viewing hood by more tapped holes. My mirror mounts have shims... We have a few distances to deal with here.

I doubt Nikon was that imprecise lens to lens, but maybe.

Randy Moe
19-Feb-2015, 18:14
http://www.largeformatphotography.info/forum/showthread.php?36782-Show-off-your-Large-Format-camera!&p=1200607&viewfull=1#post1200607

Peter De Smidt
19-Feb-2015, 19:09
Make sure the ground glass isn't in backwards. I had a Keith Camera 4x5 twin lens. I asked the person I bought it from how the pictures were from it. He said "Soft." I bet they were, as the ground glass was in backwards and silk was covering the back of the taking lens.

dsphotog
19-Feb-2015, 19:15
Have you tried swapping the lenses? To verify the lenses and mounts are identical.

mdarnton
19-Feb-2015, 19:22
Lenses are not identical; the focal length is nominal, the numbers just a convenience, and the manufacturer accepts a certain range, a couple of mm either way in a lens of that length, so you could have two lenses within specs, but at opposite ends of the tolerance. Even with small cameras, Leica's 50mm lens is a 51.7, with a small variation on either side of that. No one would normally notice or care, because how often are they used in pairs?

I bet a good repair shop could adjust them so they were the same. It's all just about $$$$, right?

Dustyman
19-Feb-2015, 20:57
Major Update!

I have discovered a small black thumb-screw that resides on the inside top center ceiling of the lower half of the camera. If you remove the back you will feel it in the ceiling of the lower picture-taking body section. This screw, when loosened, will allow you to move the mirror, in the above section, back and forth until focus is achieved on the top ground glass via the viewing lens. This is a pretty ingenious device, which allows one to "sync" the focus of the two lenses without the use of shims. Here's what you do:

a) Using a tripod, you focus critically with the taking lens (wide open, of course) on the ground glass of the 4x5 back.
b) Then, remove the back, loosen the mirror adjusting screw, and move the 45 mirror forwards or back until critical sharpness is seen on the top viewing focusing screen.
c) Once the top glass is sharp, tighten the thumb-screw, then reinstall the 4x5 back.
d) take nice pictures

I guess my mirror moved over the years and needed an adjustment. This will work only on the very late model Gowlandflex cameras (i.e., black bar handle on top versions). I have an older one (similar to yours Randy, except gray) that does not have this thumb-screw mirror adjustment. I think Peter Gowland was constantly tinkering and modifying the design and there are very few that are identical. Each one has its own refinements as well as new idiosyncrasies. That's the charm and also the source of frustration, sometimes, with these cameras.

Anyway, I hope this info comes in handy to others with similar cameras.
Thanks to all who made suggestions. You helped me to think deeper into what the variables might be.

Randy Moe
20-Feb-2015, 00:08
Major Update!

I have discovered a small black thumb-screw that resides on the inside top center ceiling of the lower half of the camera. If you remove the back you will feel it in the ceiling of the lower picture-taking body section. This screw, when loosened, will allow you to move the mirror, in the above section, back and forth until focus is achieved on the top ground glass via the viewing lens. This is a pretty ingenious device, which allows one to "sync" the focus of the two lenses without the use of shims. Here's what you do:

a) Using a tripod, you focus critically with the taking lens (wide open, of course) on the ground glass of the 4x5 back.
b) Then, remove the back, loosen the mirror adjusting screw, and move the 45 mirror forwards or back until critical sharpness is seen on the top viewing focusing screen.
c) Once the top glass is sharp, tighten the thumb-screw, then reinstall the 4x5 back.
d) take nice pictures

I guess my mirror moved over the years and needed an adjustment. This will work only on the very late model Gowlandflex cameras (i.e., black bar handle on top versions). I have an older one (similar to yours Randy, except gray) that does not have this thumb-screw mirror adjustment. I think Peter Gowland was constantly tinkering and modifying the design and there are very few that are identical. Each one has its own refinements as well as new idiosyncrasies. That's the charm and also the source of frustration, sometimes, with these cameras.

Anyway, I hope this info comes in handy to others with similar cameras.
Thanks to all who made suggestions. You helped me to think deeper into what the variables might be.

Well you are correct, mine is not adjustable that way. But I don't currently need it. Next time I take it apart I will look into that mod.

So if yours also does not have it, have you moved your mirror? Or are you saying you have 2 of these, one older one newer?

Also mine originally came with 3" inch round threaded lens 'cones' that screwed in and may have been depth adjustable. But those were missing and I had custom square boards locally made.

EdSawyer
20-Feb-2015, 06:34
Good to know about this. The other thing I was thinking is was there a fresnel involved? If that is in the wrong place (e.g. wrong side of focus screen), it will affect focus.