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Issues with 3x4 Graflok back

 
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Axon



Joined: 20 Feb 2011
Posts: 8

PostPosted: Thu Dec 22, 2011 10:37 pm    Post subject: Issues with 3x4 Graflok back Reply with quote

Hi everybody,

I have a 3x4 Anniversary Speed Graphic. It came with the original Graphic back. I bought a Graflok back from a member of this forum and installed it. There begins my trouble. Although he assured me it would work, it traps the focal plane shutter when screwed down. Okay, whatever. I use slow film and shuttered lenses. I can deal with that. But recently I've noticed focusing errors. On a landscape shoot, it consistently focused in front of the focus point I thought I set. I confirmed this with backyard focus testing today. Clearly I have installed the back incorrectly, or it was never meant to fit on my model of camera.

I found this on APUG: "Yes, the back will simply unscrew. I don't know about the pre-anny models, but on my 1946 Anniversary, I was able to install a 3x4 Graflok with no problem..." What am I doing wrong that prevents the focal plane shutter from functioning?

There is no fresnel in the Graflok back, and here are pictures of the two backs and a focus test. I mis-labeled the "Graphic" back as "Graflex" in the test.
http://imgur.com/a/V4mwD

Can anyone here shed light on my situation?
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45PSS



Joined: 28 Sep 2001
Posts: 3231
Location: Mid Peninsula, Ca.

PostPosted: Thu Dec 22, 2011 11:01 pm    Post subject: Reply with quote

1. Remove the focus panel from the Graflok back by pressing inward on the ribbed edges and sliding the frame to the right.
2. Measure the distance the lower focus panel arm frame intrudes into the camera shutter.
3. Make a shim from heavy card stock, wood veneer edging, or similar to bring the back out .010 to .020 from the curtain.
4. Reset the infinity stops and Rangefinder infinity focus point and retest.
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Axon



Joined: 20 Feb 2011
Posts: 8

PostPosted: Thu Dec 22, 2011 11:10 pm    Post subject: Reply with quote

I can do what you describe with my Century Graphic back, but this particular Graflok back has a lip that seems to prevent removal of the focus panel. Is there a separate method for 3x4 Grafloks?
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45PSS



Joined: 28 Sep 2001
Posts: 3231
Location: Mid Peninsula, Ca.

PostPosted: Thu Dec 22, 2011 11:18 pm    Post subject: Reply with quote

Can you post a picture of the Graflok back, panel side?
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Axon



Joined: 20 Feb 2011
Posts: 8

PostPosted: Thu Dec 22, 2011 11:42 pm    Post subject: Reply with quote

It is remarkably hard to manipulate a spring back with one hand.

Here are several views of the back, with my speculation added. http://imgur.com/a/0NBMF
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45PSS



Joined: 28 Sep 2001
Posts: 3231
Location: Mid Peninsula, Ca.

PostPosted: Fri Dec 23, 2011 12:40 am    Post subject: Reply with quote

http://graflex.org/speed-graphic/features.html#GraflokBack
or
http://graflex.org/speed-graphic/features.html#GraflokBack
page 21.

Push in toward the ground glass on the ribbed section.

The Grafok probably shipped as a kit to retrofit the Anniversary. The kit included a spacer to fit the edge of the camera body and space the Graflok back so that it would not interfere with the shutter. You have to make such a spacer.
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Axon



Joined: 20 Feb 2011
Posts: 8

PostPosted: Fri Dec 23, 2011 1:33 am    Post subject: Reply with quote

This is the motion you're describing, right?
http://i.imgur.com/7zk6Q.jpg

I can't, and here's why:
http://i.imgur.com/OGFO5.jpg

No amount of twisting or pushing in any direction that I can see will move this. It appears that the only way the glass can be removed is by disassembling the whole back. But, you clearly know a heck of a lot more than me, and I can't wait to be proven wrong.
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45PSS



Joined: 28 Sep 2001
Posts: 3231
Location: Mid Peninsula, Ca.

PostPosted: Fri Dec 23, 2011 3:53 am    Post subject: Reply with quote

Take the first of your last two images.

The graflok sliders are pushed in against the focus panel. Slide them to their extreme limit opposite what they are now. They are currently blocking the path the arms must move once depressed.

Press in on the arms at the arrows once the sliders have been moved to their release position and while holding them down slide the panel to the right.

Leave the graflok sliders in the release position except when using an accessory.
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Axon



Joined: 20 Feb 2011
Posts: 8

PostPosted: Fri Dec 23, 2011 4:12 am    Post subject: Reply with quote

45PSS, you've done it again. Next time I catch myself thinking, "I sure do know a lot about photography," I'll remember this day.

I removed the panel and measured the distance, and I can see exactly what I'll need to do to fix it. Thank you very much for your help.
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45PSS



Joined: 28 Sep 2001
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Location: Mid Peninsula, Ca.

PostPosted: Fri Dec 23, 2011 5:03 am    Post subject: Reply with quote

With the back removed from the camera and the focus panel installed:
1. Lay a straight edge across the back making certain the straight edge is not on a raised point or recess, measure from the straight edge to the ground glass at top, center, bottom, left, right, center. the distance should be the same at all points.
2. Insert a film holder with a scrap piece of film installed and remove the darkslide. Measure from the straight edge to the surface of the film at the same points as the ground glass. The surface of the film should be the same distance as the ground glass +/- .007 inch. Test with 2 or 3 film holders and on both sides. I have had film holders that were .003 out on one side.

If the film surface is out the same amount on all holder sides then the ground glass is out of position. Add shims to the ground glass mounting bosses between the glass and the boss to increase the ground glass distance, remove them to decrease the distance.

Once the ground glass position is correct and the back is correctly mounted on the camera mount the camera on a sturdy tripod. Focus the lens on the ground glass on an infinity target at least 5000 feet away. The farther away the target the more accurate the setting. Use a focusing loupe. With the lens in critical sharp focus on the ground glass and the front standard square to the camera bed/rails and locked slide the infinity stops up to touch the front standard frame and tighten their set screws.
Next adjust the rangefinder infinity if it is not correct. Rangrfinder focus on closer objects at 25, 15, and 10 feet and verify correct focus on the ground glass. If the ground glass does not agree with the rangefinder the rangefinder requires adjustment.

The moon makes an excellent infinity target but one must keep readjusting the camera position to keep the moon on the ground glass.
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Axon



Joined: 20 Feb 2011
Posts: 8

PostPosted: Fri Dec 23, 2011 6:16 am    Post subject: Reply with quote

Again I thank you for the advice. Simple household toothpicks proved to be perfect shims, and now the ground glass/film plane is within 1/64 of an inch tolerance.

What is the best way to shim out the entire back to free the curtain? Should the card stock go only around the edge, or is it safe to have it protrude inward toward the shutter curtain a little bit?
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45PSS



Joined: 28 Sep 2001
Posts: 3231
Location: Mid Peninsula, Ca.

PostPosted: Fri Dec 23, 2011 6:44 am    Post subject: Reply with quote

Quote:
Should the card stock go only around the edge, or is it safe to have it protrude inward toward the shutter curtain a little bit?

Should not matter as long as it does not touch the curtain or rollers.

The aperture stays (stiffeners) are .010 copper or brass folded over. When they go over the center of the roller is when the curtain will be at its highest or closest to the back.

Quote:
and now the ground glass/film plane is within 1/64 of an inch tolerance

TriX 320 in 4x5 sheet film is .007 inch thick. If the ground glass is more than the thickness of of a sheet of film different from film in a holder depth you will have focus issues.
Film holder depth is .197 from the holder edge +/-.007 inch and ground glass should match the holders. 1/64 is .015625, .001625 more than backing plate distance tolerance and .008625 over a single sheet of thick film variance. 24 or 28 bond printer paper single, double, or triple layer makes good ground glass shims also.

---
Focus errors are most noticeable at close focused distances.
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