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02-23-2019, 11:55 AM   #1
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Pentax-F 50 f1.4 ó auto aperture not working on MZ-S

I recently bought a MZ-S and attached my F50/1.4. When I dial the aperture to the A setting, the viewfinder readout shows me f32 and the body LCD shows f27 (neither of which of course the lens even has.). The camera tries to set a show shutter speed due to the tiny aperture that it thinks is set. When I dial other apertures, the camera shows the correct aperture dialed. When I attach my F50/1.7 to the camera with the aperture set to A, the camera shows whatever aperture it wants to set.

So I started thinking that my F50/1.4 has issues. I dug out my K3ii and attached the lens with the aperture set to A, and the K3ii showed whatever aperture it felt was appropriate for the light.

So I seem to have an incompatibility with that lens and that camera. The lens predates the camera by about 10 years, so I would think it would be compatibilite. Other lenses have seemed to work fine in the camera, and other cameras have seemed to work fine with that lens. (Well, the only other camer I have that can set aperture is the SuperProgram, and that seems to work.)

Has anyone encountered an issue like this before? At least I can use the lens in aperture priority and manual mode, but it is a little odd.

* the MZ-S is set to normal exposure like, not MTF or the others.

02-23-2019, 12:20 PM   #2
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Clean the contacts, it the first thing I can think of.
02-23-2019, 01:24 PM   #3
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Do other F, FA, DFA, or DA lenses work properly on the MZ-S?

If not, clean the contacts on the camera.
02-23-2019, 01:56 PM   #4
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As per each of the above... ^ ^ ^

Conventional wisdom is to clean the contacts of both lens and camera.

That being said, I am concerned about the viewfinder showing different numbers than the LCD. They should both be the same.


Steve

02-23-2019, 02:00 PM   #5
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QuoteOriginally posted by abruzzi Quote
When I dial the aperture to the A setting, the viewfinder readout shows me f32 and the body LCD shows f27 (neither of which of course the lens even has.). The camera tries to set a show shutter speed due to the tiny aperture that it thinks is set.
QuoteOriginally posted by abruzzi Quote
When I dial other apertures, the camera shows the correct aperture dialed.
QuoteOriginally posted by abruzzi Quote
When I attach my F50/1.7 to the camera with the aperture set to A, the camera shows whatever aperture it wants to set.

Tell me how this last statement is different from the two above it.
Correction: Sorry! I get it. The last refers to a different lens.


Steve

Last edited by stevebrot; 02-23-2019 at 02:06 PM.
02-23-2019, 02:06 PM   #6
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QuoteOriginally posted by abruzzi Quote
When I dial other apertures, the camera shows the correct aperture dialed.
On a wild guess, does it show f/1.7 rather than f/1.4 for wide open?


Steve
02-23-2019, 07:09 PM   #7
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QuoteOriginally posted by stevebrot Quote
On a wild guess, does it show f/1.7 rather than f/1.4 for wide open?


Steve
No, it correctly shows 1.4. I donít know enough about how the body and lens communicate to have much idea where the issue might be. I did clean the contactsófirst thing I tried, but forgot to mention. Iíve tried a few other lenses, but not all of them. Iíll play around more tomorrow, but Iím trying to decide whether itís a problem with the lens or the MZ-S. The lens Iíve had for a couple of years, so there is no refunds there, but the MZ-S was just bought from KEH, and Iím trying to decide whether this a defect in the camera, and should be returned.
02-23-2019, 08:19 PM   #8
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QuoteOriginally posted by abruzzi Quote
I donít know enough about how the body and lens communicate to have much idea where the issue might be.
Welcome to the club!

I had to do some thinking here. I am quite familiar with how the non-crippled KA mount works, but the tough part is how the MZ-S drives the aperture number for the displays. Here are a few thoughts:
  • P and Tv modes (camera controls aperture), the contacts on the mount communicate the minimum aperture and aperture range. See Features and Operation of the KA Mount | The K-Mount Page for details. For your F 50/1.4, the displayed apertures should be in the range 1.4 to 22. You should be able to test this in Tv (shutter priority) mode. If you are able to display numbers outside the actual range by changing shutter speed, there is a problem with the contacts on either the lens or camera.
  • Av and M modes (aperture ring controls). For this case, the camera "knows" the same contact information as for P and Tv modes, but depends on the actual aperture ring position for display purposes. Metering depends on aperture position coupling tab on the body which engages a similar tab on the lens. The display takes its cue from the position of the tab on the body. The maximum aperture position is the same for all K-mount lenses, while the minimum may vary depending on the range of apertures supported. In display purposes, the body "knows" the breakpoints between stops and will display as is appropriate with the minimum being either f/16, f/22, f/32, or f/45 depending on lens. Of course, this only works for lenses with contacts on the mount. (I'm assuming it works the same for A-series as for AF lenses.) For lenses without contacts, the display will be "F--" . Edit: Thanks to @Not_a_Number for clarifying a feature of the KAF mount. When the aperture ring on an AF lens is off the "A" position, the set value is passed to the camera through the "data" pin on the mount face.
If P and Tv modes display only the correct range of aperture values while Av and M modes do not, the most likely cause is an issue with the aperture position coupling between the lens and body or how the coupler position is interpreted within the body internal issue with the aperture ring position sensing on the lens.


Steve


Last edited by stevebrot; 02-24-2019 at 12:10 AM.
02-23-2019, 08:25 PM   #9
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QuoteOriginally posted by stevebrot Quote
If P and Tv modes display only the correct range of aperture values while Av and M modes do not, the most likely cause is an issue with the aperture position coupling between the lens and body or how the coupler position is interpreted within the body.
...or the aperture ring is allowing travel beyond its stop at f/22. That should not happen unless the "A" lock button is depressed.


Steve

Last edited by stevebrot; 02-23-2019 at 08:31 PM.
02-23-2019, 10:48 PM   #10
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The MZ-S is KAF2 or the so-called "crippled k-mount". Lens info is transmitted via the "data" pin on the mount.

Please re-confirm - with the camera in Av or M mode and lenses set to "A":
Check both bodies, K-3ii and MZ-S

What is the smallest aperture that can be set and displayed with each of the F lenses, e.g. F 50mm 1.4 vs F 50mm 1.7? Should be f22
What is the largest aperture that can be set and displayed? Should be f1.4 and f1.7 for the respective lens.

If both lenses shows incorrect min or max apertures on the MZ-S then the MZ-S is likely defective
If only the 50mm f1.4 lens shows incorrect min or max apertures on both bodies then likely the lens is defective.
If only the 50mm f1.4 lens shows incorrect min or max apertures on only the MZ-S then either the lens or MZ-S is defective or both - testing with other lenses may isolate if it is only the MZ-S likely at fault

One possibility that occurred to me is that some of the segments on the top LCD panel are out so some numbers will nott display properly. One of my 20 year old Casio watches suffers from this on the date display. However this doesn't explain why the viewfinder shows f32 when the max on the lens is f22.
02-23-2019, 11:58 PM   #11
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QuoteOriginally posted by Not a Number Quote
The MZ-S is KAF2 or the so-called "crippled k-mount". Lens info is transmitted via the "data" pin on the mount.
Cool! I was unaware that the data pin transmitted the position of the aperture ring with the KAF and KAF2 lenses and that is how the MZ-S gets the aperture ring information. That tidbit solves a big mystery for me. I have edited my comment above and credited you with the revelation. FWIW, the MZ-S mount is standard KAF2, not crippled (works with KA lenses in all exposure modes and non-A lenses in M and Av modes).


Steve

Last edited by stevebrot; 02-24-2019 at 12:11 AM.
02-24-2019, 12:10 AM   #12
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QuoteOriginally posted by stevebrot Quote
Cool! I was unaware that the data pin transmitted the position of the aperture ring with the KAF and KAF2 lenses and that is how the MZ-S gets the aperture ring information. That tidbit solves a big mystery for me. FWIW, the MZ-S mount is standard KAF2, not crippled (works with KA lenses in all exposure modes and non-A lenses in M and Av modes).


Steve
I should qualify that by saying "when in the A position" and only info such as focal length, focus distance, min and max apertures and variable aperture range (zooms). Since there is no mechanical link to the aperture ring on the KAF2 mount stop-down metering would be required out of the A mode.

But you know that

Last edited by Not a Number; 02-24-2019 at 12:15 AM.
02-24-2019, 12:30 AM   #13
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QuoteOriginally posted by Not a Number Quote
I should qualify that by saying "when in the A position" and only info such as focal length, focus distance, min and max apertures and variable aperture range (zooms). Since there is no mechanical link to the aperture ring on the KAF2 mount stop-down metering would be required out of the A mode.

But you know that
KAF2crippled is that way. Regular KAF2 on the MZ-S has the mechanical linkage and supports open-aperture metering in Av and M modes with all K-mount lenses. For more information on the information passed through the data pin, the "K-mount Page" has a good summary for KAF that clarified the matter quite a bit for me. Thanks for setting me on that line of inquiry.
Features and Operation of the KAF Mount | The K-Mount Page
See section on Digital Communication where the reporting of actual set aperture is covered. The KAF2 mount on the MZ-S adds power zoom and MTF data for supporting lenses.


Steve

Last edited by stevebrot; 02-24-2019 at 12:42 AM.
02-24-2019, 09:33 AM   #14
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Check the lens and camera and see if the aperture feeler actuator is firm and working correctly.

Also check your MZ-S with an DA lens to see how it reacts. Do you have any other FA lenses to do a test with?

02-24-2019, 03:35 PM   #15
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A couple of comments based on what people have asked above:

- I’ve shot some frames on the MZ-S with a DA40/2.8 and a DA70/2.4, and while I have to use Tv or M, they both seemed to work fine. In fact, every other lens works. I’ve tested the following:

DA40/2.8 Limited
DA70/2.4 Limited
F50/1.7
F28/2.8
F100/2.8 Macro
F35-70 zoom
FA 24-90 zoom

Tamron 28-200
Sigma 24/1.8

(I have some A series manual focus lenses but I haven’t tested any of them.)

They all work. The only thing I can see about all of the above, is all are slower than 1.4. The problem lens is the only 1.4 lens I have with A contacts.

- I doubt the difference between the outside and viewfinder display is a LCD segment failure because I can’t see getting from F32 to F27, and the segments display other numbers normally on this and every other lens I have tried.

- when I take the F50/1.4 off of A and dial it to any manually set aperture, the LCD correctly reports the selected f-stop.

- the feeler on the camera and the tab in the lens for communicating the set aperture all seem to be acting normally.

- A new piece of information—I’m new to the camera, so I didn’t realize that it reported the exposure mode in the LCD. When I have the 50/1.4 mounted and the aperture set to A, the camera reports “Av” mode. (Or M if I hit the dial to change shutter speed.) I’ve pressed the green button on the front to reset to P mode, but it doesn’t change. With any other lens it shows P mode when the aperture is set to A (or Tv if I hit the shutter dial. Since the feeler moves when a little when I move the aperture dial from 22 to A, I’m guessing that the camera is interpreting as moving to the next smaller aperture—which would be f32, and it’s not getting the communication from the lens saying “I’m in A mode now”.

Thanks everyone for their input. I’m leaning towards believing it is a lens issue, but I wish I had another 1.4 lens to test.
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