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11-06-2010, 07:29 AM   #1
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Oddly working Chinon on K110D

Hi

I have this Auto Chinon 50mm F1.7 lens and I think it's working in a pretty strange way.

For example when attached to camera and i rotate the aperture ring from 1.7 to 2, I can see blades moving, but after 2 they don't move. But when I rotate the aperture ring to min. aperture (F22) and start reversing towards larger aperture, the blades start moving "correctly" and obviously the viewfinder comes darker and ligther as the blades move.

Also the lens doesnt seem to stopdown correctly (using the AE-L-button) at all aperture values.

All my other non-Pentax manual lenses work unlike this, when I turn the aperture ring on those, the blades don't actually move and the stopping down works like it should.

So I would like to know if someone has any idea or even has this same lens, is there something wrong with it and if so, what could I do for it ?

P.S When off-camera blades are snappy and move fluently.

11-06-2010, 03:42 PM   #2
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Is it a K mount? or M42 mount? If it is a K mount, it will not stop down until you actually take the shot when it is attached to the camera. If it is M42, check to see if the lens has an Auto / Manual switch. If it does, and is on Auto, the lens will stay wide open. Switch it to manual, and check again..
11-07-2010, 03:19 AM   #3
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QuoteOriginally posted by Stratman Quote
Is it a K mount? or M42 mount? If it is a K mount, it will not stop down until you actually take the shot when it is attached to the camera. If it is M42, check to see if the lens has an Auto / Manual switch. If it does, and is on Auto, the lens will stay wide open. Switch it to manual, and check again..
Thanks for your input! As far as I can tell, it is a K-mount. There is no manual/auto switch.

I also thought, the lens should stay wide open when aperture ring is turned, but this doesnt!

If I rotate from 1.7 to 2 the blades move to 2 position. But when i turn it to 2.8 or further, blades dont move any more, unless i turn aperure ring other way, for example when the ring is turned to 5.6, the blades are at f2 position, but once I reverse to f4, blades snap to f4.

Anyhow I think blades shouldnt move at all when attached to camera and turning the aperture ring, am I wrong?
11-08-2010, 06:38 AM   #4
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Anyone ?

11-08-2010, 07:22 AM   #5
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QuoteOriginally posted by Xtreme Quote
Anyhow I think blades shouldnt move at all when attached to camera and turning the aperture ring, am I wrong?
you are not wrong. the camera uses a lever on the mount of the lens to stop it down when the shutter is pressed, maybe yours is broken/crooked/faulty.
11-08-2010, 01:54 PM   #6
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I have a copy of the same Chinon 50mm F/1.7.

It behaves exactly the same as other pK-mount manual lenses: when attached to the camera, it's always at full aperture no matter what setting the aperture ring is at. The aperture stops down only during taking photo or during DOF review.

As suggested, the lever of the lens may be crooked.
11-09-2010, 12:36 AM   #7
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QuoteOriginally posted by SOldBear Quote
I have a copy of the same Chinon 50mm F/1.7.

It behaves exactly the same as other pK-mount manual lenses: when attached to the camera, it's always at full aperture no matter what setting the aperture ring is at. The aperture stops down only during taking photo or during DOF review.

As suggested, the lever of the lens may be crooked.
Thanks, it might be so then. But will I break anything if I keep using it lke this?

Usually I use the lens wide open, but if I stop it down like this so that the blades actually move, could it break something?
11-09-2010, 03:58 AM   #8
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I forgot to ask, if anyone knows is there anyway of fixing the possibly broken lever ?

I don't mind actually using the lens like this, if i can be sure, it doesn't break anything.

11-09-2010, 10:32 AM   #9
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I got this cracked today, thanks to your advices.
I slightly pulled the aperture pin further from the body, cause it seems to be a bit bended or so, and now it works as it should.

Although, I'm not quite sure, which way I liked it more, cause when it was working faulty, I was able to "stop it down" in av-mode
11-09-2010, 11:45 AM   #10
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QuoteOriginally posted by Xtreme Quote
Although, I'm not quite sure, which way I liked it more, cause when it was working faulty, I was able to "stop it down" in av-mode
If you want to use it in stop-down mode in Av mode, do this:

- Remove the lens from the camera.
- Use a piece of tape (ScotchBlue™ Painter's Tape is my favorite for marking) on the camera, near the lens mount, mark the location of the lens locking pin.
- Attach a piece of tape around the lens barrel.
- Set the aperture ring of the lens to the largest number (e.g. F/22).
- Attach the lens to the camera while looking into the lens, notice when the lens closes down to smallest aperture. Put a mark on the tape around the lens barrel, aligning with the mark of the location of the lens locking pin.
- Drill a small hole on the lens mounting ring at the mark. You may need to remove the mounting ring to do this. It's pretty simple, just a few screws. The new hole is similar to the existing hole, just about 1/2 inch to a side. The size of the hole is not critical, as long as it's equal to or larger than the size of the existing hole.

If you want to use the lens in stop-down mode, lock the lens with the new hole. If you want the original functionality, when attaching the lens to the camera, depress the lens locking lever pass the first (newly-drilled) hole and lock the lens with the original hole.

There, you have it both ways.
11-09-2010, 01:36 PM   #11
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Thanks a lot for that instruction!
I might actually do that!
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