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05-21-2022, 12:31 PM   #1
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Does film door play affect film flatness of Pentax 67?

A question for any users of the Pentax 67. Recently I again aquiered a Pentax 67 with some lenses. I am satisfied with the results, but when using smaller diafragm values especially with the 150/2.4 @ f/2.4, I notice some (not all) photo's have the focus significantly off and behind the subject. Also, the focus seems to vary across the frame. After doing several tests, including verifying the position of the focusing screen with respect to the focal plane, testing the lenses with a digital camera, I cannot come to a different conclusion that the film is not exactly flat against the pressure plate. It must be curved inwards, although only slightly perhaps within 0,5 mm. At this moment I still have some unexposed frames left so I haven't had the chance to open the door, but what I notice is that the door can be pressed in a little before reaching the back of the camera. My question: is this normal or should it close tightly? I have not had any light leak issues so the foam seems to be fine. Please let me know your opinion and what is normally seen.

05-21-2022, 01:19 PM   #2
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Interesting and I would think it does have an effect, just a guess. Maybe as you take the remaining exposures, press the door if possible to test it.
05-21-2022, 01:26 PM   #3
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QuoteOriginally posted by Tom67 Quote
A question for any users of the Pentax 67. Recently I again aquiered a Pentax 67 with some lenses. I am satisfied with the results, but when using smaller diafragm values especially with the 150/2.4 @ f/2.4, I notice some (not all) photo's have the focus significantly off and behind the subject. Also, the focus seems to vary across the frame. After doing several tests, including verifying the position of the focusing screen with respect to the focal plane, testing the lenses with a digital camera, I cannot come to a different conclusion that the film is not exactly flat against the pressure plate. It must be curved inwards, although only slightly perhaps within 0,5 mm. At this moment I still have some unexposed frames left so I haven't had the chance to open the door, but what I notice is that the door can be pressed in a little before reaching the back of the camera. My question: is this normal or should it close tightly? I have not had any light leak issues so the foam seems to be fine. Please let me know your opinion and what is normally seen.

It does have a pressure plate, so it's possible.

Pentax 67 120 vs 220 setting - PentaxForums.com
05-21-2022, 02:26 PM   #4
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Thanks! Ok the two left frames i'll try to push the door while firing the shutter. Let's see..

05-21-2022, 06:09 PM - 1 Like   #5
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If it has a pressure plate, that plate should be spring loaded meaning the back door can be expected to move a bit without moving the film plane (which is established by the pressure plate and the film rails). If there's too much play in the door however, the pressure plate may be losing it tension and be unable to press the film flat against the film rails. In that case, it would be an issue.
05-21-2022, 09:01 PM   #6
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QuoteOriginally posted by Tom67 Quote
After doing several tests, including verifying the position of the focusing screen with respect to the focal plane, testing the lenses with a digital camera, I cannot come to a different conclusion that the film is not exactly flat against the pressure plate. It must be curved inwards, although only slightly perhaps within 0,5 mm. At this moment I still have some unexposed frames left so I haven't had the chance to open the door, but what I notice is that the door can be pressed in a little before reaching the back of the camera. My question: is this normal or should it close tightly?
I dont and never have shot the 6x7. But I have shot 120 and 35mm film a lot back in the day. All of the systems I have used have pressure plates which are spring loaded and the aim is to have tension to press the film flat on the rails. Typically film that is rolled has a bias to arch upwards away from the film plans and bow away from the lens not towards it. The doors tend to be pretty solidly shut and while you could force them inward due to the pressure plate springiness it typically would warp the door on 35mm. The 6x7 is much larger so there might be more play? But Id be cautious as too much pressure could cause the seals to fail to seat fully as the door flexes and cause light to leak. Id inspect the pressure plate and be sure it is set for the right film as some cameras are adjustable to work with 120 and 220 and the thickness difference matters.
05-22-2022, 12:28 AM   #7
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QuoteOriginally posted by Bob 256 Quote
the pressure plate may be losing it tension and be unable to press the film flat against the film rails. In that case, it would be an issue.
I agree, the whole point of the pressure plate is to keep the film smashed flat against the rails, since the 67 isn't an auto advance camera you can set the pressure plate as firmly as you want to (within reason). Some films like T-MAX have thicker film bases than more common filmstocks and because of this, some people like to tweak the pressure plate a bit to make it easier on the crank mechanism to advance the film this could have been the case with your camera.

05-22-2022, 08:57 AM   #8
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There is no 'tweaking' the pressure plate on the P67. It would be a significant hack.
05-22-2022, 01:16 PM   #9
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Thanks for the replies, after the film roll was shot and removed I placed a piece of roll film in it and set the camera to bulb and opened the shutter without lens to have a look.
The film seems to be complete flat even though there is no paper backing to the film. The pressure plate springs are fine. So I have the impression that the camera seems to work properly.

If any film uneveness should occur, it must be caused by the film.. could it be that the films nowadays are different than the film material that was used in the 90's and 00's? That time i had never any issues. Now, when I receive the negatives back from the lab, the negatives are generally very curved, much more than I was used to. This poses challenges in the scanning too, but I am confident that the problem is not in there, since the film grains look evenly sharp across the frame.

Anyway, I have taken a number of f/2.4 pictures with this film, let's see in two weeks what it delivers.
Attached is the look at the film through the camera.
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05-22-2022, 10:24 PM   #10
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Were it me, I might even try a roll switching the film plate to the 220 setting which will slightly increase the pressure, but leaving the counter switch set to 120, just to see if it makes any difference.
If there is significant resistance in the advance, I'd abandon the experiment.
It's also worth noting, though maybe obvious, if the camera hasn't been in for a CLA in recent years and it's new to you with unknown history... couldn't hurt.
What film were shooting? Some are certainly thinner than others. That shouldn't really make a difference but for a camera that's out of sorts, it can. I've a Pentacon that gives me spacing issues regularly with certain, thinner stocks.
05-28-2022, 06:58 AM   #11
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It is unlikely to be a factor in your problem, but some film stocks are definitely curlier than others. I gave-up on Rollei RPX25 because of it.


curl par Kris Lockyear, on ipernity
06-01-2022, 03:24 PM   #12
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Are you viewing flatbed scans? Getting an edge-to-edge sharp scan with 120 roll film can be a problem when scanning the film lying flat especially with thin, curly films. Scanning on the tanget of an arc like with drum type scanners does much better in that regard.
06-02-2022, 12:33 PM   #13
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I am using a digital camera setup with the lomography film holder to scan the negatives. So not ideal when it comes to flatness. But I am convinced that the problem does not lie in there, I did multiple scans and manually focussed accurately at full aperture, when i took the image I closed the aperture so the depth of field should be sufficient. Saturday I expect a new developed film with prints back from the la, a roll where I took some more shots at the full f/2.4 aperture with the 105 mm lens, so I hope to be able to better judge what might be the issue.
06-02-2022, 06:30 PM   #14
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How can you judge edge-to-edge sharpness of a scan with an image taken at f2.4 with that 105mm? My Coolscan 9000ED has a glass carrier. There is a little gap between the glass. And that scanner has auto focus. Some shots/film would scan edge-to-egde pretty good but many not so well. Hopefully scanning with a DSLR has more DOF than my scanners do.

Last edited by tuco; 06-02-2022 at 06:36 PM.
06-03-2022, 01:57 AM   #15
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Sorry for the confusion, the film image was taken with P67 105 mm, I scan the images with a Fujifilm digital APS-C camera with Loawa 65 mm Macro lens. The subject distance is about 30 cm. According to DOF calculator, the depth of field with f/8 aperture and 0,02 mm coc is roughly 2 mm at front and 2 mm at back, so just sufficient to get decent results across the frame. Mid of the frame is accurately focussed thus sharp.
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