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John_shriver
Tinkerer
Username: John_shriver
Post Number: 47
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 29, 2009 - 05:43 pm: | 
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So I have a couple of 1A and 3A Autographic Kodak Special with Rangefinder cameras. The first Kodak cameras with rangefinders. But I'm trying to determine the best strategy for calibrating the rangefinders.
First problem is getting everything to agree. For instance, on the two 1A cameras, the rangefinder agrees dead-on with the focusing scale. Both the stop that pushes the sliding lens for the rangefinder, and the focusing scale, are riveted in place. So trying to move them seems futile. So I need to collimate the lens to focus at infinty (or 100 feet) when the rangefinder is at 100 feet.
One way would be to shim the lens relative to the front standard. But one lens will need something like 3mm of shimming, and the nut isn't going to get a grip on the shutter with that much shim. So that's not very practical.
The other approach is to adjust the focal length of the lens by changing the spacing of the two lens cells. For instance, on the 1A with repaired bellows, that needs the lens 3mm further out, I need the lens to be a shorter focal length. So if I back out one cell, the focal length will get shorter, and I can collimate it. Seems practical, although I've never seen any shims to set that distance in any of these Kodak cameras.
The second question is what to use as the focal plane for collimation. I check with a ground glass I took out of a TLR. (Leftover after installing one of Rick's nice split-image screens.) But 116 or 122 roll film doesn't wind up that flat in a folding camera. No way. So that results in front-focusing, since the film is further away from the lens than I collimated for.
So does anyone have a recommended "fudge factor" for 116 or 122 rollfilm cameras? Or for 120 ones, for that matter? Wasting precious rolls of 116 or 122 film to calibrate focus is not appealing!
I know what Topcon calls for in their Super D repair manual, but they hold 35mm film much flatter than these rollfilm cameras.
Or, does anyone have old Kodak service manuals on these old "Special with Rangefinder" Kodaks? |
Nickon51
Tinkerer
Username: Nickon51
Post Number: 108
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, November 01, 2009 - 06:21 am: |
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I'm not quite sure what you mean here John. Why would placing a ground glass screen on the film rails not work? The film is held in place by pressure rails or a pressure plate like any other roll film camera.
I would pull out the standard and set it to 100' as you suggest, and slide the lever back and forth to check for best focus on the ground glass.
Although the lever and distance scale are riveted in place, the latch for the standard is held in place by a couple of screws whose holes are slotted for adjustment. Unlatch the front standard and slide it back a bit and you should see it.
Best of luck. It would be nice to see some photos out of one of these.
Having 100 feet set on the film plane, you would then go ahead and adjust the rangefinder to correspond. |
John_shriver
Tinkerer
Username: John_shriver
Post Number: 49
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, November 23, 2009 - 07:51 pm: |
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The adjustable stop for the front standard doesn't have the right range of travel to make the lens agree with the focusing scale and rangefinder.
That's why the only remaining degree of freedom I can see is adjusting the focal length of the lens.
Many cameras call for a shim between the ground glass and the rails when calibrating focus, to compensate for non-flat film. For instance, the Topcon Super D is designed for 0.06mm of film curvature. A 116 rollfilm camera will have more film curvature than that. How much I don't know.
With the narrow DOF of the lens, the rangefinder is useful, but only if accurate.
I'm considering hanging a tiny LED flashlight inside the bellows, putting in a roll of 116 film with an X on the emulsion, and collimating with an SLR focused to 100 feet. |
Charlie
Tinkerer
Username: Charlie
Post Number: 223
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, November 24, 2009 - 05:34 am: |
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Can you build up the film rails the desired thickness to space the film further from the lens? |
Nickon51
Tinkerer
Username: Nickon51
Post Number: 114
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, November 28, 2009 - 07:16 am: |
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I was not aware of the method of using a shim when adjusting the focus on the film plane. I agree that if you are worried about the film not seating flat across the plane the the method with and X on a piece of film, and collimating with an SLR would be the next best thing.
As you know the infinity focus at the film plane has to be right before anything else. I would imagine that the film lever is put in the infinity or 100 ft position and the adjustable stop moved for best results. Shimming the lens would be needed if infinity focus cannot be achieved by the stop alone. Then adjust the rangefinder to suit.
I wonder what sort of error we are talking about here? a few thou, a mm or more?
Good luck
Greg |
Nickon51
Tinkerer
Username: Nickon51
Post Number: 115
Registered: 05-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, November 28, 2009 - 07:24 am: |
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OK I just reread the first post. 3mm is way too much if the lenses are the originals.
I would do the film plane focus with the lever at the correct position for infinity or 100ft. That will tell you whether the lever is out of position, or the range finder out of adjustment. |
Glenn
Tinkerer
Username: Glenn
Post Number: 724
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, November 29, 2009 - 06:38 am: |
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You are approaching this problem arse about face. Assuming that your cameras are original and not mucked about with, you need to ascertain the reason for the 3mm 'error' or difference found between the examples. My understanding is that whilst these cameras were hand assembled, they were not 'hand fitted', ie individually assembled with parts chosen to minimise the overall manufacturing tolerances. So find out what is worn, broken or otherwise wrong and do not work to dimensional tolerances that were not there in the first place.
I must add that in my 'formative' years I seemed to be surrounded by these and other Kodak models. My father's parents had an old photographic studio and attached shop, there were draws full of cameras in various states of dereliction that I played with - much as one would Meccano. When the ability to 're-assemble' surfaced one summer - I was eleven, house bound and on a long recovery from serious illness - I eventually manage to fudge up some 'workable specials'. I still have four of the cameras in question; I suppose they should be viewed as the very first items of photographic equipment I collected, whilst that seemingly endless summer certainly steered me into my eventual profession.
Sadly my darkroom skills were sadly lacking in those days; that, the use of very old film and Printing Out Paper has resulted in very few images remaining from this important period of my life. |
John_shriver
Tinkerer
Username: John_shriver
Post Number: 52
Registered: 12-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, February 28, 2010 - 03:07 pm: |
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I finally had another bout with the 1A's today, and I think I found the right calibration method. The stop on the bed of the camera pushes against a cylinder that screws onto a peg on the moving lens segment in the rangefinder. You adjust that cylinder by unscrewing it until the rangefinder agrees with a ground glass. I did this at 6 feet and 20 feet, and it looks like it will be accurate. Not film tested yet, a very gray day today.
The lenses do not have consistent focal length. Two two I have differ by a good 3 to 4mm in focal length. This is obvious by looking at where Kodak riveted the focusing scale down to the fixed bed -- they are at different locations on each camera. So there was definitely some hand calibration in assembling these -- parts are not interchangeable from one camera to another.
Similarly, the stop on the bed that the cylinder on the moving lens hits was located by Kodak at time of manufacture, it has a long slot, with a screw through it. But once they screw it down, they drilled another hole, and riveted it in place.
The one I got adjusted has such a short focal length lens that you can't really put the infinity stop on the moving bed in the right place. So you need to pull the front standard out a few mm short of the full way. That's OK, because the stop on the bed has nothing to do with the calibration of the rangefinder or focusing scale.
If I can get this focusing accurately, then I will invest either the time in making a good bellows, or pay to have one made. |
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