[Not a Number]

How very odd. I have a K10D and the Super-Takumar 135mm f/3.5 screwmount lens and genuine Pentax m42 K-mount adapter and I can confirm that the aperture does not close down when I press the green button in manual mode and lens set to "A"uto.

I repeat No K-mount body has the mechanism to auto stop-down screwmount lenses.

Here is a Spotmatic II. The Auto Stop-Down mechanism can be seen at the bottom of the lens mount opening.


Here is a K10D. Other than the power zoom contacts there is no other mechanism at the bottom. Certainly nothing that would operate the pin on a screwmount lens. The K-mount auto stop-down actuator tab can be seen on the left (9 o'clock) in the mirror box. Remove the lens and adapter. When you press the green button you will see and hear this tab move. Does anything by the power zoom contacts move?


If you have a mechanism at the bottom of the mirror box hold on to that body as you have something totally unique. Post some pictures. Better yet take a video with your K-1 looking through the front with or without Takumar mounted on the K10D showing the stop-down in operation with the green button.

Note: The actuator will always operate on the K10D regardless if or what type of lens is mounted. The K-5 and later models including the K-1 series the actuator will only operate with lenses that short out the "data" pin. That's why you don't hear the actuator on the K-1 with screw-mount lenses unless you use an externally flanged bare metal adapter.

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Last edited by Not a Number; 07-01-2018 at 05:28 AM.

[Snakeisthestuff]

Ok guys, I have to apologize!

I checked this today again and even though the camera makes this noise, which I always associated with aperture closing, it does not move the diaphragm.

I guess I got fooled by the noise from that motor or spring load or whatever.

[monochrome]

^^ Asahi screwmount lenses don’t stop down with the Green Button on my K10D either. I use the method described by ‘Not a Number’ above.

[monochrome]

Ok guys, I have to apologize!

I checked this today again and even though the camera makes this noise, which I always associated with aperture closing, it does not move the diaphragm.

I guess I got fooled by the noise from that motor or spring load or whatever.

I think you are hearing the K-mount stop down lever moving.,

[Snakeisthestuff]

I am really sorry, I think my false memories plus the sound of the lever fooled me in thinking it worked.

Thanks everyone for your help especially @not a number, i learned a lot.

[pschlute]

Ok guys, I have to apologize!

I checked this today again and even though the camera makes this noise, which I always associated with aperture closing, it does not move the diaphragm.

I guess I got fooled by the noise from that motor or spring load or whatever.

No worries. I use a K1 now but still have my trusty K10D also so I knew that wasn't correct for M42 lenses.

I find Av mode works best with the screwmount lenses. I focus first at wide open then stop down to the required aperture. If the exposure is not to my liking I will switch to manual.

[stevebrot]

The original Pentax adapter allows infinity focus, but I’m not sure if they’re still made, or not.

They are still made, but often in short supply in some markets.


Steve

[UncleVanya]

Yes it does xD.
As already told, I have confirmed this with my K10D already.
When I press the green button there I hear and see the aperture closing temporarily for correct metering.
My K-1 on the other hand does not do this while using the same lens with same adapter.

FYI: The genuine pentax m42 to K adapters are still for sale in Japan, where I got mine.

There is some miscommunication here somewhere. The thread I linked clearly calls out the process for using m42 and the k10d is specifically mentioned.

Can you upload a video clip of how this is working on the k10d? It isn't supposed to be possible, there is no mechanical linkage between the aperture actuator in the camera and the m42 lens aperture pin, mechanically those do not work the same way at all. The auto/manual switch on many m42 lenses does open and close the blades, which is why most people use open aperture in Av mode, focus and compose, then flip the switch, and the body pics the right shutter speed. The camera has no way to know anything about aperture on these lenses, and no way to interact with the aperture pin to enable it to control anything aperture related. Lastly there isn't any calibration to the pins, it's all or nothing, unlike the A series where a specific amount of travel of the lever gives predictable (mostly) changes in aperture.

[stevebrot]

There is some miscommunication here somewhere.

I think the OP resolved the issue (see above comments).


Steve