Focus Adjustment for Metal Camera

[coisasdavida]

Are the holders new to you too? Wood and metal? Could someone have been using them to shoot paper negatives (thick stuff)? That can loosen the lips that hold the film back. Plastic holders wouldn't be a problem, I guess paper negatives wouldn't fit...

[N Dhananjay]

Is this with all holders? Have you tried a relatively new, solid holder? That is, have you eliminated the holders as the source of the problem? I suppose it is possible for the odd camera to be out of spec the more troublemsome way. If it is what you have described, the only solution seems to be the removal of some material - given the somewhat drastic nature of that surgery, I'd want to be extra sure that I have eliminated all other sources of error before I cut into the patient. Cheers, DJ

[Ari]

Thanks, Guilherme and DJ.
The camera is clean, I went over it when I first got it; GG is installed properly, and looks true.
I have three holders, all of them plastic Fidelity Elite; I have shot paper negs on occasion, they work fine for that purpose too.
As to DJ's query, I will go through the holders again, and see if there is a problem there; you're absolutely right about re-checking everything else before working on the camera.

[C. D. Keth]

It's a good call to check your holders if you haven't already. I got some wooden eastman 5x7 holders several years ago that caused a similar problem. It turned out that some wiseguy thought they were all beat up and would look nicer if he planed a couple thousandths off and re-stained them.

I'm trying to think of anything else that might help before you have someone alter part of the camera itself.

[Ari]

Postscript:

I did some more measurements last night of the GG and each film holder.
The KMV has a hole in the bed where the tripod plate goes, so I closed the camera and measured the depth from the lip of the hole to the GG or film holder (with film inserted).

To my surprise this time, I got a reversal of my last readings: the GG is closer than the film plane.
I took multiple readings of everything, and after averaging it all out, I found that the GG has an average depth of roughly 0,5mm difference with my best (closest) film holder.

I will now proceed to shim accordingly, and of course, cross my fingers.

Thanks for everyone's help, I really appreciate it.

[Roger Hesketh]

Which lens were you using? You said wide open. What was the aperture used and what was the focused distance?

The questions may not seem relevant but they are. All are variables which will determine the depth of focus that you have at the film plane. With the answers to the above questions I should be able to work out the depth of focus that you should have available at the film plane with that lens, aperture and focused distance combination. Happy to supply you with the tools, depth of focus tables, so you can do it for yourself. Then you can work out if any measured disparities are significant. What you don't want to be doing is spending money correcting things that will not have a a significant effect in the first place.

Using the lenses and apertures that we tend to use for L.F. photography certainly for 8x10 were the focal lengths used are longer and their is more depth of focus. Depth of focus, that is the distance either side from the plane of principal focus were a focused image appears sharp is really quite large and allows a fair amount of wiggle room. Rather more than one might expect. With miniature cameras e.g. 35mm depth of focus is minute. With 8x10 depending on the aperture used, focal length of lens and focused distance it can extend several mms either side of the plane of principal focus.

[ic-racer]

the GG is closer than the film plane.

If that is the case your negatives show sharp focus of subjects closer to the camera than what the ground glass shows. This seems to contradict you original post.

[Ari]

Roger, I was using a Commercial Ektar 12" wide open; shutter was set to bulb for a one-minute exposure.
Distance was about six feet away.
I understand what you're saying, but all I see is a point of focus where it shouldn't be, wide open or not.
Depending on how far away I am shooting, I understand that the effect will vary, but it will still be there.
Thanks.

To my surprise this time, I got a reversal of my last readings: the GG is closer than the film plane.

IC, I am contradicting myself; my measurements told a different story the second time around.

I think I have found the real problem, it seems to be a slightly warped camera back.
Will investigate further, but nothing permanent has been done to the camera so far.

Thanks again.

[N Dhananjay]

It may not be a warped back but a 'tired' spring back. In other words, the spring that holds the back tight against the camera body has become weak in the normal position. I have seen this on many older cameras - so the back actually sags off the body a bit in use. When you insert the holder, the spring tightens up since it has been put under tension (the film holder pushes the back away from the camera body) and holds the film holder tight against the back. Cheers, DJ

[Ari]

DJ,
Thanks, but if I lay the back down on a flat surface, one corner sticks up.
I also spent some time bending the springs to eliminate them as possible errors.