[womble]

I'm hoping this isn't the dreaded cog problem (it doesn't sounds as if it is...).

I finally gave in to GAS and bought an MZ-S. It is in almost immaculate condition (although missing the rubber bits that turn to goo). The first roll I ran through it was a mixed bag with groups of frames exposed correctly, and groups badly under-exposed. As I had been swapping lenses between the FA31mm, F35-70 and the K50/1.4 I couldn't be sure whether it was me doing something silly. The second film (Kodak Tri-X) was shot entirely with the FA31, virtually all on a single day. The vast majority of frames are vastly under-exposed. They were shot in program mode with exposure compensation dialled in where judged necessary.

Any suggestions as to what might be the problem? I guess the next test would be to measure exposure with another camera or my hand-held meter and compare that to the readings given by the camera.

Given how super (cosmetically) the MZ-S is, and how nice it feels in the hand (small, but solidly built and excellent design), I'm a bit peeved that the results are so dire.

Thanks, Kris.

[ismaelg]

Hello,

The gear failure of the other MZ/ZX will cause the mirror to stay up. This sounds like a metering issue. Starting with the obvious, Is the meter set to spot? Do you know if it is reading DX properly? Compensation inadvertly set? Clean meter cells? Not sure where they are in this model. I agree a side by side comparison with another camera or meter would be a good test. Also, check to see if the lenses are closing properly or if for some reason they are closing all the way down. Keep us updated. That is a beautiful and capable camera.

Thanks,
Ismael

[gofour3]

The vast majority of frames are vastly under-exposed. They were shot in program mode with exposure compensation dialled in where judged necessary.

I only use my MZ-S in aperture priority with the matrix metering. Exposures seem right on with any type of film that I've used, including E100 slide film.

I would check each of the cameras Pentax functions using the manual and see if anything looks like it's set weirdly.

Phil.

[AlwaysAl]

This may be far out there but a question; is the focusing screen sitting correctly in its tray and properly latched? Recall having a similar concern after replacing a focusing screen. Jut a thought. Reviewing the Forum, there was a good illustration by member Catalana here: https://www.pentaxforums.com/forums/115-pentax-k-5-k-5-ii/142225-focus-adjust...nt-images.html

[TwoUptons]

I wonder if it could be an issue where the lens is in "A", and the camera is trying to set the aperture at a reasonable place, but the camera for whatever reason is stopping the lens down all the way to f22 (or whatever the FA31 does).

Do you think the exposures as you saw them in the viewfinder represented what the camera was doing? If you were seeing 1/2000 at f16 with Tri-X, you have a metering issue

I don't know what would cause different behavior between various lenses outside of some communication error...
Have you cleaned the contacts on the body/lens interface?

-Eric

[womble]

Hi folks,

many thanks for all the comments. I checked various things suggested. The metering agrees with my K-3iii and my handheld meter.

The problem occurs when the lens is set to A. Whatever the meter is saying, the lens stops down to its smallest aperture (without increasing the shutter speed). So, the meter may be saying f/2.8 @ 1/60, but the lens lens shuts down to f/22 and the shutter speed doesn't change. I've checked this with my FA31 Ltd and with a F35-70 and the same thing happens with both. I tried just cleaning the contacts with a dry cloth, but that didn't make any difference. If I use Av mode (i.e., take the lens off A and let the camera choose the shutter speed), everything works as expected.

Not sure what I do now.

Thanks, Kris.

[OldChE]

Did you try cleaning the contacts on the camera mount? Maybe the camera isn't communicating correctly with the lens.

[Dartmoor Dave]

It sounds like exactly the same symptoms as aperture solenoid failure in a digital body -- extreme underexposure when controlling the aperture from the body with the lens set to A, but correct exposure when using the aperture ring to set the f-stop.

Does the MZ-S use an aperture solenoid to control the diaphragm from the body? The parts list is inconclusive. It lists the aperture control block as a single component, see item 0-G100 on fig.2 of this link:

https://learncamerarepair.com/downloads/pdf/Pentax-MZS-Parts.pdf

So it looks like that entire component would need to be replaced, if the part is even still obtainable, which is likely to cost as much as the camera itself. I think your best option is to only use the camera with lenses that have an aperture ring, and only use exposure modes that don't need to control the diaphragm from the body. At least with the MZ-S you've got an uncrippled mount, which should make life a lot easier.

Edit: Are the correctly exposed frames on your first roll the ones that you shot with the K50/1.4? If that's the case then it would confirm that you've got an aperture block problem, because with the K series lens you definitely would have been using the aperture ring.

[womble]

Did you try cleaning the contacts on the camera mount? Maybe the camera isn't communicating correctly with the lens.

Yes I did.

[womble]

It sounds like exactly the same symptoms as aperture solenoid failure in a digital body -- extreme underexposure when controlling the aperture from the body with the lens set to A, but correct exposure when using the aperture ring to set the f-stop.

Does the MZ-S use an aperture solenoid to control the diaphragm from the body? The parts list is inconclusive. It lists the aperture control block as a single component, see item 0-G100 on fig.2 of this link:

https://learncamerarepair.com/downloads/pdf/Pentax-MZS-Parts.pdf

So it looks like that entire component would need to be replaced, if the part is even still obtainable, which is likely to cost as much as the camera itself. I think your best option is to only use the camera with lenses that have an aperture ring, and only use exposure modes that don't need to control the diaphragm from the body. At least with the MZ-S you've got an uncrippled mount, which should make life a lot easier.

Edit: Are the correctly exposed frames on your first roll the ones that you shot with the K50/1.4? If that's the case then it would confirm that you've got an aperture block problem, because with the K series lens you definitely would have been using the aperture ring.

Thanks Dave.

Short answer is that I don't remember. I am, however, going to shoot another test roll using just my K50/1.4, I have no idea if it uses a aperture solenoid but it does sound as though that might be the problem. Thankfully, all my "full frame" lenses have aperture rings and most of them are older manual glass anyway. If it works fine in aperture priority mode then I can live with that, although it is annoying.

Thanks, Kris.

[OldChE]

My MZ-S works fine in all modes with old and new lenses, so I don't think this is a problem with the model features. Do you have any Pentax-A series lenses to try? You can see if they work when set to A mode, they are a bit less complicated than the later autofocus lenses, but still have the automatic aperture. I was thinking that the camera was not picking up that the lens had an automatic setting (hence the question about the contacts), so it was operating as-if the lens were a manual aperture lens. In that case the aperture would probably default to fully stopped down on the lens side.

[womble]

I'll try an A series lens in the morning.

K.

[womble]

I have just got my test roll back shot entirely using Av mode rather than Program mode and the images are all perfectly exposed. The problem definitely lies with using a lens set to A. It is annoying (I dislike having faults with my cameras) but it is one I can live with.

Thanks for all your helpful suggestions.

Kris.

[womble]

One frame from the roll. A selection can be found here.


taxi! par Kris Lockyear, on ipernity