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07-23-2019, 05:16 PM   #1
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Can film SLR split-image focusing screen systems go haywire? If so how & what then?

I've been getting ready to shoot some film again in my Sears-labeled Ricoh film SLRs and discovered something surprising that I never noticed before -- two of the three seem to have focus problems, when using their spit-image circle in the center of their (original and unchanged) focusing screens.

The three camera's, with their Ricoh names first, are:

* the Ricoh XR-1s (Sears KS1000)

* the Ricoh KR-10 (Sears KSX)

* the Ricoh KR-10 Super (Sears KSX Super)

The main differences between the models are that (1) the XR-1s has a manual shutter, while the other two have electronic shutters that only work at one speed without batteries; (2) the KR-10 and KR-10 Super both offer Aperture-Priority exposures, while the XR-1s does not; (3) the XR-1s and the KR-10 have match-needle light meters, while the KR-10 Super has a Liquid Crystral Display of a needle over a shutter speed scale; and (4) the KR-10 Super can go as slow as 16 seconds for manual or A-P exposures.


One thing all three have in common is diagonal split-image circles at the center of their viewfinder screens. One would expect these to all function identically, but today I discovered that they do not.

EXAMPLE :

* If I put my Auto Sears MC f/1.8 lens on the XR-1s, and focus on an object (specifically on the frame of the TV set from sitting in my living room easy chair) using the camera's split-image circle in the viewfinder, the scale on the lens shows the object as being about 8.5 to 9 feet away -- which looks to be accurate.

* If I put the same lens on the KR-10, and focus on the same object while seated in the same location, surprisingly the scale on the lens now shows the object to be 10 feet, or slightly farther, away -- close enough to accurate that I might not have noticed it if I weren't doing this comparison.

* If I follow the same procedure, but with the lens on the KR-10 Super, the lens distance scale now reads north of 15 feet, which isn't very far from the 30 feet label, the interpolated value could easily be considered to be about 18 to 19 feet -- more than double the actual distance.

One other thing, I don't think the lens has any responsibility in these different focusing behaviors, since I have taken excellent and precisely focused pictures with it when using it on my Pentax ME Super film SLR body.

I've read that people who replace focusing screens can have problems if they are not shimmed and checked properly. These do not see seem to be screen replacements.

I don't suppose there is an easy adjustment to correct the problem with the KR-10 Super's very aberrant split screen behavior?


[Another other thing -- it would be against forum rules for me to post this in the Pentax Film SLR Discussion category where more readers knowledgeable about this issue would likely be hanging about, even though Ricoh now owns Pentax and even though finding dozens of examples of that rule being ignored can be found in that category. So I have posted this query here in General Photography.]

07-23-2019, 11:10 PM   #2
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The prisms of a split image screen might be set at different angles, Pentax used to offer different screens for faster lenses for MX & LX, improving accuracy with wide aperture lenses. The drawback is that these prisms 'blackout' much sooner (wider apertures) than normal screens. Think of it as being equivalent to a longer rangefinder baseline.

You can see a change between a Super-A (from an era of mainly fast primes) to an MZ-M (where slower zooms were the norm), the latter prisms black out about f/5.6 or later while the former starts about f/4. All else being equal, the Super-A should be more accurate with fast primes (larger DoF with slower lenses might cancel this out).
07-24-2019, 01:38 AM   #3
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As you mentioned yourself it could be a question of the shims which are used to adjust the position of the focusing screen. If the screens are user-exchangeable, then a do-it-yourself fix is possible, otherwise a repair shop can do it. Or perhaps the focusing screen has been put in upside down?

It could perhaps also be that the mirror on the bad copy isn't positioned in the required 45 degree angle due to worn (or missing) components such as the stops in the walls of the mirror box.
07-24-2019, 01:51 AM   #4
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The registration distance from the flange to the focus screen (via mirror) should be the same as from flange to film: 45.46mm on all K-mount cameras.

Differences could be because of the above mentioned screen design, built-in diopter of the viewfinder, focus screen or mirror out of adjustment.

Check the focus in the viewfinder using a non-split image portion of the screen. A viewfinder magnifier will help. Blackout of the split image can be overcome somewhat by shifting the position of your eye along the axis of the split line - usually left-to-right.

Is the image in focus on the film on all the bodies? If not the screen, mirror and/or diopter needs adjustment.

07-24-2019, 08:10 AM   #5
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Thanks johnha, Ole, Not A Number !

Unfortunately, my first suspicions came about the bad slr copy came AFTER I had loaded it with film and was taking some pictures with it using my Auto Sears MC f2.8 28mm during the middle of the day yesterday. For some of the shots I used the depth of field guide marks on the lens to shoot at a hyperfocal setting, and since I've had no problem with that lens on other cameras (including dslrs), those exposures shouldn't have a problem. I see no reason to suspect that the flange to film distance could have changed on the body.

I noticed problems first when I had to crank the lens much closer to infinity for things that weren't that far away, but since 10 feet and infinity aren't that far apart on wide-angle lenses, using a 50mm seemed better for the test I used to introduce this thread. That's when I started comparing the split-image focus setting to the reading on the lens distance scale, and sometimes also compared it to focus settings I got using the outer ground glass area of the focusing screen, particularly when focusing at closer distances when these different results seemed to conflict the most.

* As for viewfinder eyepiece lens diopter, it isn't user adjustable in this camera model, though the viewfinder lens might have shifted or be defective.

* I don't believe that focusing screen replacement was a general option for any of these models, not that technicians might have been able to do it. Again, I assume that all three of these cameras have their original screens, and if any of these screens are out of adjustment it is probably due to something shifting, breaking, or disappearing.

* Mirror angle could be an issue, though I don't feel equipped to measure or correct the angle. The mirror had been occasionally sticking up, but recently by careful application of naphtha droplets to spots that might have had some had some congealed lube, I got the mirror sticking to disappear. I don't think that servicing could have caused the mirror angle to be off, but perhaps it was already off, due to "worn or missing components" as Ole theorized.

* I believe all three of these cameras' split-screen areas have trouble with slow-maximum aperture lenses, beginning to black-out or worse, as johnha states affects some Pentax split-screens did, necessitating other focusing screen options being needed for those lenses. With these cameras the main option is to use the outer areas of the focusing screen if the center blacks out due to slow maximum apertures or low-light conditions.

My temporary solution to having shot a half a roll of film in the body with the most aberrant split-screen behavior, has been to rewind the film and transfer it to the most accurate of these three bodies, and winding past the already exposed portion.
09-01-2019, 01:12 PM   #6
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Not the focusing screen per se but there are things that can upset it.

I'd bet on mirror angle being off IF the film shows focus issues but VF split screen doesn't. Setting the mirror angle would be a job for a camera tech I suspect. The factory probably had some kit to check it but I have no idea how you would do it as a DiY.

Some cameras had shims added to the underside of the focusing screen to slightly adjust its height and some have adjusted on the prism for the same reason. Same problem - a camera tech may be able to fix it but I have no idea how a DiY fix would work.

The lens markings may not be 100% if someone has disassembled the lens barrel/focusing ring and not correctly reset it and zeroed it properly.
09-01-2019, 07:36 PM   #7
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Mirrors can most certainly go way out of adjustment. I have an old spotmatic that is way off.
09-02-2019, 07:46 AM   #8
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A while back I got the scans from the roll of Kodak T400CN chromogenic B&W I shot half in the Sears KSX Super, with the split-image focusing way off, and half in the Sears KS1000, which seemed to have the most accurate split-image focusing of my three Sears/Ricoh K-mount film camera bodies. Two funny things happened:

(1) I had hardly any focus issues in the exposures with the first camera, meaning apparently I compensated for the problem sufficiently by eye-balling distances, using hyperfocal settings, and using the microprism focusing part of the screen just outside of the split-image center.

(2) I got better exposures with the KSX-Super than with KS1000 (with the more accurate split-image focusing). It may be that the KSX-Super takes a center-weighted light reading, while the KS1000 merely averages everything coming in, or perhaps the KS1000 meter is a bit off.

The upshot, is it makes me more curious about whether there is a way to fix the focusing issue with the KSX-Super, either by shimming the mirror or the focusing screen or by replacing the screen with one without the split-image area.

Meanwhile, I should be getting back scans in a day or so from the roll I shot in the Sears KSX, which gave split-image focusing distances closer to the KS1000.

09-02-2019, 08:02 AM - 2 Likes   #9
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If one of the film cameras (or even a DSLR that you own) has got known good infinity focus, you can use it to collimate your other cameras (assuming you can get the focusing screens out to re-shim them). Here's a guide to how to do it:

Camera repair pages

Although the guide talks about adjusting the focusing helical on your lens, you can also use this method to re-shim your focusing screen as long as both lenses used are already set correctly at their infinity stops..
09-02-2019, 08:47 AM   #10
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QuoteOriginally posted by Dartmoor Dave Quote
If one of the film cameras (or even a DSLR that you own) has got known good infinity focus, you can use it to collimate your other cameras (assuming you can get the focusing screens out to re-shim them). Here's a guide to how to do it:

Camera repair pages

Although the guide talks about adjusting the focusing helical on your lens, you can also use this method to re-shim your focusing screen as long as both lenses used are already set correctly at their infinity stops..
Thanks for the link, Dave. That is certainly a procedure that I would have never imagined in a million years--to use a second camera. Hmmm?
09-02-2019, 12:19 PM   #11
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The guide that I linked to in a hurry earlier makes it seem more complicated than it actually is in your case, as you wouldn't need to do all that taping film to the back of the camera stuff with two SLRs, since the focusing screens are at the same distance as the film plane. Just set the cameras face-to-face with the lenses both set to infinity, then look through the viewfinder of the camera with the known good focusing screen and look at the focusing screen of the camera that needs adjusting. Re-shim until the markings on the focusing screen of the camera to be adjusted are in focus when viewed through the known good camera.

Oh, darn. I'm doing a terrible job of explaining this. It's such a ridiculously simple thing when you know what it is, but it's really hard to explain it to someone who's never done it.
09-02-2019, 12:31 PM - 1 Like   #12
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QuoteOriginally posted by Dartmoor Dave Quote
The guide that I linked to in a hurry earlier makes it seem more complicated than it actually is in your case, as you wouldn't need to do all that taping film to the back of the camera stuff with two SLRs, since the focusing screens are at the same distance as the film plane. Just set the cameras face-to-face with the lenses both set to infinity, then look through the viewfinder of the camera with the known good focusing screen and look at the focusing screen of the camera that needs adjusting. Re-shim until the markings on the focusing screen of the camera to be adjusted are in focus when viewed through the known good camera.

Oh, darn. I'm doing a terrible job of explaining this. It's such a ridiculously simple thing when you know what it is, but it's really hard to explain it to someone who's never done it.
As someone who hasn't done it my interpretation is basically.

- Use known good camera to reach a specific focus point
- Shim misaligned camera until the focus points match and achieve a matching clarity between both camera's viewfinders.
- Celebrate!
09-02-2019, 12:34 PM   #13
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QuoteOriginally posted by ZombieArmy Quote
As someone who hasn't done it my interpretation is basically.

- Use known good camera to reach a specific focus point
- Shim misaligned camera until the focus points match and achieve a matching clarity between both camera's viewfinders.
- Celebrate!


Yep, that's pretty much it, using infinity as the known good focusing distance.
09-02-2019, 02:39 PM   #14
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I think I will have to first take a broken film slr body I have no intention to repair or have repaired and practice removing and reshimming the mirror and the focusing screen before I try to work on one of these cameras.
09-11-2019, 08:34 PM   #15
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I check this with a spare split screen on the film rails and a loupe, I think it's about 8x or 10x on B, with a focus target. Same process as shimming a dslr, though much more difficult to move the screen position. It's most likely the mirror position as other people have said, for the person above with the spotmatic, it's just a matter of bending the little tabs the mirror comes down on, but you need to be able to match the finder and film plane accerately. I've cut off 5.32nds or so from the left and right of the screen I use for the film plane so ut just rides on the inner (film) rails. prism towards the lens.
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