[Larrea]

Hello.
I want to start a repair project.
You see: My new RICOH SINGLEX II cannot complete the shutter cycle as the mirror is stopped shortly before reaching the bumper but only when the lens is mounted.
It is an AUTO RIKENON 1:2 50mm - M42.
In this lens, the cam that operates the diaphragm sticks out 3.7 mm (5/32") and is capable of closing fully at f/16 with a force of less than 80 grams (2.8 oz) leaving only 2 mm (3/32") sticking out. Pushing it all the way down requires increasing force to just under 250 grams (8.8 oz) to do anything (All according to my Chinese SF-400 digital scale). It seems that this final effort is too much for the mechanics of the camera.
On the other hand, the red mark on the lens appears to be off-center from the place that it would seem logical to occupy with the lens firmly attached, as seen in the photo.

My inquiries:
1) Do the forces used seem logical to you?
2) Don't you think it could have been disassembled and reassembled incorrectly?
3) Will any of you have information about the disassembly procedure for this lens or a clone to guide me through an almost certain review? I can't find any information.
Thanks.

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[DonV]

Have you another lens to try?
Is your lens fully seated it stops turning/screwing in?

[Larrea]

Hello DonV.
At the moment and thanks to the pandemic, there are no other M42s to cross-test.
And yes... The lens is screwing all the way.

[mtkeller]

The red marks on Takumars are frequently off-center on Pentax bodies, so I wouldn’t fret over that part of things. That’s about all I have to contribute here, unfortunately. I would probably try to find another M42 lens cheaply on eBay for comparison purposes.

[Larrea]

Thanks, mtkeller
I have just verified your interesting contribution through Google images. Some lines "advance" and others "fall behind" at 12 o'clock.
It would be great if someone with some scale and curiosity measured the operating forces of the cam. Because 80 gr seems reasonable; but 250 gr seems excessive to me.
Thanks.

[stevebrot]

It would be great if someone with some scale and curiosity measured the operating forces of the cam. Because 80 gr seems reasonable; but 250 gr seems excessive to me.
Thanks.

The action of the aperture actuator pin should require very little force to stop down the lens and the action should be "snappy". The pin length and amount of travel to stop down varies, though what you describe sounds quite typical. It is normal to have significant resistance when attempting to push it further. It is unlikely that or the stop-down action of the lens is the direct cause of the problem. I don't own the Auto Rikenon 50/2.0, though I do have an Auto Rikenon 50/1.7. Its pin length and action is similar your description.

Are able to use the camera meter or depth-of-field preview button with this lens? Viewed from the front, does the lens stop down fully to f/16 if so set? If so, the aperture actuation "flipper" in the camera is able to engage the pin to stop down the lens. With lens off the camera, does the "flipper" move up and forward decisively to the actuation (vertical) position and does it hold the position even when pressed lightly with a finger? The reason I ask is that there is an interlock between the mirror and the flipper position. If it is not fully homed to the vertical position, the mirror will stop midway. At least that is how it works on my mechanically similar Singlex TLS.

My suspicion is that the fault lies with the camera.

I hope this helps.


Steve

[Larrea]

Hi Steve.
Yes: The preview button works and stops down at f/16 without problems. The flipper advances with determination as far as it can go when pressing the button.
As long as that button is pressed, it will remain in that position until a noticeable external counter force of about 200g (7oz) begins to move it as if it were defeating a spring.
Unfortunately my measurements are not as reliable as I would like. The values are approximate.
Attached images of the flipper's route when pressing the button.
Thanks for answering. Opinions are welcome.

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