Focus Adjustment for Metal Camera

[Ari]

Hi,
I recently bought a Kodak Master 8x10 and noticed that my last few negs have been slightly soft, specifically the camera seems to focus just slightly behind the spot where I am focusing.
I did a crude measurement using a digital calliper, and found that the GG needs to move slightly closer to the film plane.

I've read about using shims on wood cameras, but never read about moving the GG closer on a metal camera.
It being a metal camera, I am hesitant to start filing it down, but maybe I shouldn't be too concerned.

Any thoughts on the best way to proceed?

Thanks in advance.

[Mark MacKenzie]

I think I would adjust your film holders before doing any permanent damage to a camera.

[evan clarke]

I think I would adjust your film holders before doing any permanent damage to a camera.


IMHO, don't mess with the holders, they should remain standard for use on other cameras. I would pull the GG and see if there are shims under it. Is it installed with the ground surface to the inside??

[Ari]

Mark, I agree with Evan: the film holders should remain untouched.
Evan, there are no shims under the GG, and it is installed properly.
It seems the ideal solution is to find a machinist well-versed in camera mechanics.

[Mark MacKenzie]

I am definitely talking out of my hat (without experience) but my thinking was that for an 8x10 people usually only have a few holders. Surely there is some procedure from Kodak to adjust for this. Using a file on the camera seemed pretty radical. Good luck with it!

[Ari]

Is there anything stuck to the bottom side of the GG frame that might be preventing it from sitting tight against the camera back? Are the springs still tight? These cameras were pretty well machined by Kodak and shouldn't need any additional work. It is possible you got a lemon, but I imagine the previous owner would have had the same issue.

Thanks, Greg; no, I cleaned everything off, and there are no obstructions under the GG.
Springs have already been tightened by me, and the film holder rests snugly when inserted.
The previous owner never used the camera, and in my test shots before buying, I wrote off the slight softness as movement on the sitter's part.

[Jac@stafford.net]

The Kodak Master is my most accurate 8x10 camera. I second the suggestion to check to be sure the ground glass faces the lens.

Some lenses shift focus when stopped down. Did you check focus stopped down?

[Ari]

I didn't stop down, I shot wide open; ground glass is properly installed.
Thanks

[Brian C. Miller]

Ari, from what you've described, the film plane is closer to the lens than the viewing plane of the ground glass. How is the GG installed? Is the ground side of it facing you or the lens? If it is facing you, then turn it around towards the lens, and then you can shim it back out to where it needs to be.
Now, it could be that for the age of your camera, the holders were wooden and made by Kodak. So it could be that your camera is correct for the matching Kodak holders. You can experiment with a holder by gluing bits of film on the edges with a removable glue like Elmer's white glue. Do that with one holder, and after you're done then you can just remove the shims with water.
There is another option, of course. Use a soft portrait lens wide open, and then you can always point to the lens and the most obvious culprit. ;)

[C. D. Keth]

Is there any slop or wiggle in the rear standard when it's locked down? I recently bought an 8x10 master view and it was quite sloppy and had to be fixed to really be useable. If yours needs help, I can send photos of what I did to fix it. It's doable with hand tools, I don't know your workshop/handiness situation.

[Ari]

Chris, I saw your post about fixing the slop; mine has very little, and it doesn't affect front-to-back anyway; thanks.
By my crude measurement, the ground glass plane is farther away than is the film plane; hence the reason for my original inquiry.

[C. D. Keth]

Chris, I saw your post about fixing the slop; mine has very little, and it doesn't affect front-to-back anyway; thanks.
By my crude measurement, the ground glass plane is farther away than is the film plane; hence the reason for my original inquiry.

That's so strange for a mass machined metal camera. Is the focus shift the same everywhere in the frame? Is the back straight and not warped? Maybe a paintjob to blame?

[Ari]

I will bring it to a machinist to have a look since I can't figure out the problem.
Everything is clean and reasonably tight on this camera.
The focus shift is localized; it focuses slightly behind where it's supposed to.

Thanks

[Jac@stafford.net]

Ari, while the thread might be ending, would not the GG actually need to be pulled farther back to correct for rear-focus? That would mean the glass requires shims.

Or is my sleeplessness showing?

[Ari]

Jac, I get this confused as well; my measurements showed the GG was farther back from the film plane.
My test sheets show that actual focus happens a little bit behind where I focus the camera.

[C. D. Keth]

Jac, I get this confused as well; my measurements showed the GG was farther back from the film plane.
My test sheets show that actual focus happens a little bit behind where I focus the camera.

If focus on film is further from the camera than you focused, then the film is indeed closer to the lens than the groundglass.

[Jac@stafford.net]

If focus on film is further from the camera than you focused, then the film is indeed closer to the lens than the groundglass.

Thanks for that.

I would have been very surprised if the back supporting the ground glass was so far out of spec in the wrong direction. Shimming is the practice.

Now for a question - where can one find sets of shims? I have a modest supply from military aerial cameras which I can snip to fit, but for the rest a source would be good. ...and automotive filler gauges are not appropriate.

Great discussion here!

[C. D. Keth]

Thanks for that.

I would have been very surprised if the back supporting the ground glass was so far out of spec in the wrong direction. Shimming is the practice.

Now for a question - where can one find sets of shims? I have a modest supply from military aerial cameras which I can snip to fit, but for the rest a source would be good. ...and automotive filler gauges are not appropriate.

Great discussion here!

Any good sheet metal supplier will sell shim stock in many thicknesses. Shims aren't needed, though. Read that bit again and visualize it: the film is indeed closer to the lens than the groundglass. The groundglass does need to go deeper into the metal frame as Ari stated.

[Ari]

How far off is it? I assume you are talking about mere thousandths of an inch.

Enough that I notice softness in photos in the areas that should be sharp.

I think it was about one fifth of a millimetre, but I will check again tonight.
I don't have proper depth gauges, just a digital calliper.

[coisasdavida]

I would remove the GG frame and look underneath for something glued/bent there.
I would check if the GG isn't to tight, maybe distorted.

[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.

[Richard Wasserman]

Ari,

While you are checking things, I suggest that you make sure that your front and rear standards are parallel. It could be that you are introducing some unwanted tilt or swing.

[Ari]

Hi Richard,
As a matter of course, I always make sure the standards are parallel before shooting; my KMV's front standard doesn't lock up super-tightly, so it's important to check each time I take a shot.
Thank you for the suggestion.

[Roger Hesketh]

Glad you found the problem. The warped ground glass frame will be the problem.

Even when focused at infinity with a 12 inch lens at f6.3 lens the depth of focus will extend 1.8mm either side of the plane of principal focus.

That figure will become larger upon focusing closer. In that respect it differs from depth of field were as you focus closer you gain less depth of field. I suspected that with none of the other suggestions that had been made for instance regarding misplacement of ground glass, holders not holding the film flat enough etc would have been of a magnitude to effect the image on the film. Cumulatively they might have done so though.

Roger

[C. D. Keth]

Even when focused at infinity with a 12 inch lens at f6.3 lens the depth of focus will extend 1.8mm either side of the plane of principal focus.
Roger

I guess that would be why the ANSI spec for 8x10 holders is +/- .016" or a whopping +/- .41mm. That seems like a huge margin until you consider the length of lens used on 8x10.

[Roger Hesketh]

Yes Chris exactly the only time it might possibly be an issue is if using very short lenses wide open when focused at infinity.

[Jac@stafford.net]

Any good sheet metal supplier will sell shim stock in many thicknesses.

Good idea.


Shims aren't needed, though. Read that bit again and visualize it: the film is indeed closer to the lens than the groundglass. The groundglass does need to go deeper into the metal frame as Ari stated.

Thanks for clearing that up. I was confused.

[Ari]

Thanks for the responses.
I hope that someone with more skill than I possess can re-true the back; otherwise it'd be a looooooong wait to find a spare.

[C. D. Keth]

Thanks for the responses.
I hope that someone with more skill than I possess can re-true the back; otherwise it'd be a looooooong wait to find a spare.

I don't know metalwork all that well but I'm sure it can be trued by the right person with the right equipment. If that doesn't work for some reason, I bet you could adapt a 2D or similar back. It would be ugly but it would work fine in a pinch.

[John Koehrer]

Is it possible to have it (mating edge) flat and then shim the GG out?

[erie patsellis]

If you bring it to a moderately competent machinist, as in somebody 50-60+ years old, tell him you need it straightened and I'm pretty sure with a well placed whack or two he'll have it lying straight again.

[erie patsellis]

Also, it would be prudent to take both pieces with you to lay them on a surface plate and find out which is bent. I'd put money on both....

[Ari]

Thanks, Erie; that's exactly what I plan to do.
So far, I've tried machinists who were referred to me by friends; I have yet to hear from one of them.
They're a funny bunch, don't answer phone calls, messages, etc.

The shop I called said they could do almost everything, but one thing they wouldn't do is straighten out the camera back.
They're pretty funny too.

I'm losing hope in the local machinists, but I do have a good one two hours away.

[C. D. Keth]

Good luck, Ari. I'm sure one of them will be able to do what you need. Out of curiosity, why wouldn't the last machinist do it?

[Ari]

Thanks, Chris.
He said since it could probably be done by anyone, and it's a hit-and-miss affair, he wouldn't want one of his guys spending time on it.

[erie patsellis]

Gotta find the old retired guy with a well equipped garage.

[wombat2go]

Hi Ari, I have a marking out table that I use for my camera projects and a basic milling attachment on the lathe.
Can you post a photo of the plate with an arrow to where you measured the warpage?
If it is die cast Al it may fracture if impact is used to try to straighten it.89639

[Ari]

Gotta find the old retired guy with a well equipped garage.

Found him; he's been in his garage so long, he forgot how to dial a phone number. :)

[Ari]

Hi Ari, I have a marking out table that I use for my camera projects and a basic milling attachment on the lathe.
Can you post a photo of the plate with an arrow to where you measured the warpage?
If it is die cast Al it may fracture if impact is used to try to straighten it.89639

Hi W2go,
I will certainly post it; I was also kind of worried about cracks and such if a hammer were to be applied.
My thinking was that a press of some kind could exert just enough pressure to true it, but I know nothing about this stuff.

Thanks for adding to the discussion.

[Jody_S]

I would be more concerned about why it warped in the first place. I don't see any data anywhere on production years for these, but there's a possibility it's affected by zinc pest (http://en.wikipedia.org/wiki/Zinc_pest).

[Ari]

Hi Ari, I have a marking out table that I use for my camera projects and a basic milling attachment on the lathe.
Can you post a photo of the plate with an arrow to where you measured the warpage?
If it is die cast Al it may fracture if impact is used to try to straighten it.89639

Here is the camera, looking at the lower right-hand side; the problem corner.
The affected area, where the warp is apparent, is in red.
Thanks

http://farm9.staticflickr.com/8230/8487376938_d5eee80bf9_c.jpg (http://www.flickr.com/photos/zsari/8487376938/)
P1000795 (http://www.flickr.com/photos/zsari/8487376938/) by Ari4000 (http://www.flickr.com/people/zsari/), on Flickr

[Jody_S]

If nothing else, anyone with a vertical milling machine and an hour or two's time could make you a new piece out of solid aluminum. Which, if it ever bent, could be simply hammered straight. That casting cannot (almost certainly not without breaking it).

[Jim C.]

It would seem to me that the GG frame could be also be milled back to flat and shimmed back to
the correct distance rather than making a whole new frame.

[jp]

Is that a crack in the lower corner or just an imperfection in the red?

If not, you could build it up with JBweld. Use a depth gauge to straddle the corners and verify glass distance.

[Ari]

That isn't a crack in the frame; I coloured the affected area in PS, so it may just be an after-effect of my poor drawing skills.

[Ari]

Just to follow up, I had a local guy measure and fix everything on my KMV.
I added some Toyo holders and it is now working like a charm; focus is bang-on.
The back was warped, and he trued it; then measurements were taken, and everything is now aligned.
I shot some test sheets, and focusing was perfect; just to be on the safe side, I also used a 12x loupe to double-check (it wasn't the problem before, but I left nothing to chance).
The proof is in the film, so I will hopefully have a few decent shots to post soon.

Thanks for everyone's help and input.