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06-08-2019, 04:06 PM   #1
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Slow shutter on 645Z

I got about 7 black frames out of around 50 photos this morning. It acts to me like a failing shutter assembly. Photos are black, but with extreme editing can be brought back to life, though not good enough for use, just good enough to show that there was in fact a photo. I was getting maybe 2-3 bad photos, then 5-6 good ones, then a few more bad ones..Wondering if anyone else has any different ideas before I ship it out for repairs. I was using the Pentax 645 90mm f 2.8 lens at the time. I will attach one of the bad photos so the EXIF data will show up for review. Any thoughts will be appreciated.

CORRECTION: Contrary to above, lens in use was the Pentax 67 55mm f 4.0 with the Pentax brand P67-P645 adapter.

Attached Images
View Picture EXIF
PENTAX 645Z  Photo 
View Picture EXIF
PENTAX 645Z  Photo 

Last edited by ivanvernon; 06-08-2019 at 04:09 PM. Reason: To add correction note.
06-08-2019, 04:58 PM   #2
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The fact that there is a photo there, although grossly under exposed, means that the shutter opened and closed for the exposure.

A slow shutter would generally result in overexposure. The shutter open for too long.

The image seems to cover the whole frame at the same relative brightness, so the problem does not seem to be the mirror obscuring part of the image.

What about the lens diaphragm? As you are using the P67 to P645 adapter, what is happening with the lens. Is it stopping down to the selected aperture? Could it be stopping all the way down to the minimum aperture of the lens? Which would result in gross underexposure.

I suggest:
  1. Try another 67 lens on the P67 to 645 adapter
  2. Try another adapter
  3. Try native 645 lenses on your camera.

This should help you decide if it is the lens, the adapter or the camera which is not functioning as expected.

Regards

Chris
06-08-2019, 06:32 PM   #3
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QuoteOriginally posted by seventhdr Quote
The fact that there is a photo there, although grossly under exposed, means that the shutter opened and closed for the exposure.

A slow shutter would generally result in overexposure. The shutter open for too long.

The image seems to cover the whole frame at the same relative brightness, so the problem does not seem to be the mirror obscuring part of the image.

What about the lens diaphragm? As you are using the P67 to P645 adapter, what is happening with the lens. Is it stopping down to the selected aperture? Could it be stopping all the way down to the minimum aperture of the lens? Which would result in gross underexposure.

I suggest:
  1. Try another 67 lens on the P67 to 645 adapter
  2. Try another adapter
  3. Try native 645 lenses on your camera.

This should help you decide if it is the lens, the adapter or the camera which is not functioning as expected.

Regards

Chris
Chris: Thank you for these observations--good reasoning. I will try your suggestions.
06-09-2019, 06:21 AM   #4
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QuoteOriginally posted by seventhdr Quote
The fact that there is a photo there, although grossly under exposed, means that the shutter opened and closed for the exposure.

A slow shutter would generally result in overexposure. The shutter open for too long.

The image seems to cover the whole frame at the same relative brightness, so the problem does not seem to be the mirror obscuring part of the image.

What about the lens diaphragm? As you are using the P67 to P645 adapter, what is happening with the lens. Is it stopping down to the selected aperture? Could it be stopping all the way down to the minimum aperture of the lens? Which would result in gross underexposure.

I suggest:
  1. Try another 67 lens on the P67 to 645 adapter
  2. Try another adapter
  3. Try native 645 lenses on your camera.

This should help you decide if it is the lens, the adapter or the camera which is not functioning as expected.

Regards

Chris
I tried the Pentax 67 75mm f 2.8 this morning and no problems at all. I will continue trying other alternatives as you suggest.

06-09-2019, 08:27 AM   #5
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QuoteOriginally posted by ivanvernon Quote
I tried the Pentax 67 75mm f 2.8 this morning and no problems at all. I will continue trying other alternatives as you suggest.
What was the AUTO/MAN lever on the 6x7 lenses set to? If the 645/6x7 adapter is like an extension tube, then the lenses needs to be on MAN for the 645Z metering to work.

Phil.
06-09-2019, 08:39 AM - 1 Like   #6
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The 67 lenses have to be in "Auto" aperture mode to work correctly with the 645, I believe I have read somewhere. The Auto/Manual selector on my two 67 lens examples suggests that the intent was to have it fall out of Manual with the least of effort. However, what I can't easily evaluate is what is actually going on in the lens when it and an adapter are connected and on-camera. Mine seem to work OK.

Beyond Chris' good advice above, you might check that your suspect lens has both its axial lever and radial iris tab functioning correctly without binding, and that this carries through to when it is connected to the Pentax adapter's two lever arrangement.

Edit: W.r.t. Phil's comment, the Pentax (and Fotodiox) adapters carry the iris drive and iris report connection to the 645.

Last edited by kaseki; 06-09-2019 at 08:46 AM.
06-09-2019, 08:59 AM   #7
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The adapter manual says it better (but perhaps less than optimally). See below. In other words, the intended aperture has to be set manually; there is no "A" setting. However, the iris stays open until the camera forces the iris closed during the image taking process if the switch is set to Auto.
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06-09-2019, 10:45 AM   #8
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QuoteOriginally posted by kaseki Quote
The adapter manual says it better (but perhaps less than optimally). See below. In other words, the intended aperture has to be set manually; there is no "A" setting. However, the iris stays open until the camera forces the iris closed during the image taking process if the switch is set to Auto.
Sure appreciate comments by seventhdr, gofour3, and kaseki. I will be working through all this information and advice, and will report back in due time.

---------- Post added 06-09-19 at 02:09 PM ----------

QuoteOriginally posted by kaseki Quote
The adapter manual says it better (but perhaps less than optimally). See below. In other words, the intended aperture has to be set manually; there is no "A" setting. However, the iris stays open until the camera forces the iris closed during the image taking process if the switch is set to Auto.
Thanks for this set of instructions. Fortunately I already knew and understood parts 1 and 2 of your comments, and have already been using the 67 lenses properly as per these two points.

I am not entirely familiar with the term "click stop, outer bayonet mounting lens," although for any given lens I have always been able to determine how to use the lens automatically in order to accomplish open aperture metering and stopped-down exposure.

The perplexing aspect of getting these over-exposed frames is that I am obtaining both good and bad photos with exactly the same camera and lens (Z and 67-55mm/4.0) settings--two photos one immediately after the other and no change in camera settings and lens settings. However, still using the same camera and the same Pentax brand adapter, but with the Pentax 67 75mm f 2.8 lens instead of the Pentax 67 55mm f 4.0 lens I do not get any black, over-exposed frames.

Testing continues . . .


Last edited by ivanvernon; 06-09-2019 at 11:10 AM.
06-09-2019, 03:49 PM   #9
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QuoteOriginally posted by kaseki Quote
Edit: W.r.t. Phil's comment, the Pentax (and Fotodiox) adapters carry the iris drive and iris report connection to the 645.
OK thanks, good to know!

The 6x7 extension tubes are manual, so no info is passed to the 6x7/67/67II cameras metering system. You can focus with the 6x7 lens DOF leaver in the AUTO position, but have to move it to MAN to get any meter reading.

Phil.
06-10-2019, 08:47 AM   #10
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QuoteOriginally posted by ivanvernon Quote
...
The perplexing aspect of getting these over-exposed frames is that I am obtaining both good and bad photos with exactly the same camera and lens (Z and 67-55mm/4.0) settings--two photos one immediately after the other and no change in camera settings and lens settings. However, still using the same camera and the same Pentax brand adapter, but with the Pentax 67 75mm f 2.8 lens instead of the Pentax 67 55mm f 4.0 lens I do not get any black, over-exposed frames.

Testing continues . . .
Because there is no electrical communication between the lens and camera, and also because of my heartfelt hope that there is nothing wrong with the camera, the only remaining aspect that I can see is the mechanical connections related to the iris. And because the other 67 lens works OK with the adapter, then I would put on my +4 diopter glasses and carefully inspect the two lenses mechanical interfaces for any differences. For example, are both the "suspect" lens' iris interfaces free of any bend or wear relative to those of the "good" lens? Does rotating the aperture setting on the "suspect" lens always cause the related lever to move correctly on the adapter's camera interface?

With the "suspect" lens on auto, and the camera ON, fixed ISO, and in some aperture priority mode, does the estimated exposure time shown in the viewfinder with a half shutter button press change as the aperture setting on the lens is manually changed? (I'm not sure of this one as I haven't tested it, but somehow the iris setting has to be known without an electrical reading, and this knowledge has to be obtained either before or during exposure for the camera to set the exposure time.)
06-10-2019, 09:57 AM   #11
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QuoteOriginally posted by kaseki Quote
Because there is no electrical communication between the lens and camera, and also because of my heartfelt hope that there is nothing wrong with the camera, the only remaining aspect that I can see is the mechanical connections related to the iris. And because the other 67 lens works OK with the adapter, then I would put on my +4 diopter glasses and carefully inspect the two lenses mechanical interfaces for any differences. For example, are both the "suspect" lens' iris interfaces free of any bend or wear relative to those of the "good" lens? Does rotating the aperture setting on the "suspect" lens always cause the related lever to move correctly on the adapter's camera interface?

With the "suspect" lens on auto, and the camera ON, fixed ISO, and in some aperture priority mode, does the estimated exposure time shown in the viewfinder with a half shutter button press change as the aperture setting on the lens is manually changed? (I'm not sure of this one as I haven't tested it, but somehow the iris setting has to be known without an electrical reading, and this knowledge has to be obtained either before or during exposure for the camera to set the exposure time.)
Thank you for this information/suggestions. Now, however, even with the 55mm lens, I cannot get a repeat on the black frames. From all the fine comments/suggestion that you and others have made, I am strongly suspecting a lens iris problem and not a camera problem. I love this 55mm and find it among the sharpest Pentax medium format lenses--and I have almost all of both the 645s and the 67s. On the other hand, you can pick up copies of the 67/55 for peanuts nowadays, less than $200 last time I looked. I catch myself wishing Pentax had reworked the 55/4.0 to create a 55/2.8 the way they did with the 75/4.5.

Thanks to all, and will report any further developments in this same place.
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