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04-09-2015, 10:47 AM   #1
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Chinon lens won't stop down on K3

HI all. I recently added a Chinon MCL 200mm F3.3 lens to my collection, and tried it out for the first time today. I'm having a problem with it, and hope those in the know here might be able to advise me!

The lens is entirely manual and is, allegedly, compatible with K mount cameras. The aperture ring rotates and clicks smoothly and positively, and - with the lens not mounted on the camera - controls the aperture correctly. Moving the aperture lever back and forth on the lens mount causes the aperture to open up and stop down as expected.

I'm using "M" mode, with the camera set to allow use of the aperture ring, and all of my other manual lenses work just fine. With the Chinon mounted on the camera (either the K3 or K5), the aperture is fully open, but when I press the green button to meter, or use the DOF function on the camera for the same purpose, the lens doesn't stop down - I hear nothing at all, and see no movement whatsoever.

The mount on the Chinon is black (painted or anodised) whereas my other lenses have unpainted mounts, and I'm wondering if this may be the issue. I've read of situations where people scraped off the paint on the lens mount to complete an electrical circuit on their Pentax DSLRs.

Can anyone shed any light on this? I've attached a pic of the lens mount...

Many thanks

Mike

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04-09-2015, 10:51 AM   #2
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QuoteOriginally posted by BigMackCam Quote
The mount on the Chinon is black (painted or anodised) whereas my other lenses have unpainted mounts, and I'm wondering if this may be the issue. I've read of situations where people scraped off the paint on the lens mount to complete an electrical circuit on their Pentax DSLRs.
Yep, that's it.
04-09-2015, 10:52 AM   #3
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I assume you have checked to see if it stops down when it is of the camera.
04-09-2015, 10:58 AM   #4
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QuoteOriginally posted by Rimfiredude Quote
I assume you have checked to see if it stops down when it is of the camera.
Yes, it works perfectly off the camera...

04-09-2015, 11:03 AM   #5
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I have a couple of lenses that do the exact same thing. Most recently a Cosinon lens that has the non conductive (painted or plastic) mount.

The easiest way that I have found to take care of this, without doing anything that is destructive to the lens is to go to the hardware store and pick up a roll of aluminum tape. It comes in different thicknesses, so just buy the thinnest tape you can and apply a piece to the mount on the lens where the contact pins normally are on an "A" series lens. This will short out the connections on your camera just like any other lens would do and your lens should work normally. The tape is so thin that it doesn't seem to effect infinity focus (at least it never has on any of my lenses) and it is easily replaced or removed if you need to for any reason.

Steve
04-09-2015, 11:10 AM   #6
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QuoteOriginally posted by Odinz Quote
I have a couple of lenses that do the exact same thing. Most recently a Cosinon lens that has the non conductive (painted or plastic) mount.

The easiest way that I have found to take care of this, without doing anything that is destructive to the lens is to go to the hardware store and pick up a roll of aluminum tape. It comes in different thicknesses, so just buy the thinnest tape you can and apply a piece to the mount on the lens where the contact pins normally are on an "A" series lens. This will short out the connections on your camera just like any other lens would do and your lens should work normally. The tape is so thin that it doesn't seem to effect infinity focus (at least it never has on any of my lenses) and it is easily replaced or removed if you need to for any reason.
Steve, this is very helpful. I'd like to resolve the issue without resorting to scraping paint off if at all possible, as the lens is in beautiful condition. Your solution sounds ideal - thank you!

Mike
04-09-2015, 11:12 AM   #7
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Stick a bit of tin foil under the lens when you mount it to short the contacts. If it works then, you have your answer.
04-09-2015, 11:13 AM   #8
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QuoteOriginally posted by Odinz Quote
The tape is so thin that it doesn't seem to effect infinity focus...
It couldn't possibly (if it mounts) because you're still locking in the bayonet, but it could interfere with mounting itself with the extra friction/thickness. It might even be smart to put a bit of tape on each side so the extra pressure is not asymmetrical, but it is very slight so it probably doesn't matter...

04-09-2015, 11:57 AM   #9
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QuoteOriginally posted by jatrax Quote
Stick a bit of tin foil under the lens when you mount it to short the contacts. If it works then, you have your answer.
Yes, in fact I just tried that before I read your post and it works

Now I just need to find some *very* thin sticky-backed aluminium or copper foil...

Thanks for your help, folks.
04-09-2015, 12:28 PM   #10
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QuoteOriginally posted by BigMackCam Quote
Yes, in fact I just tried that before I read your post and it works

Now I just need to find some *very* thin sticky-backed aluminium or copper foil...

Thanks for your help, folks.
You should only short the "data/digital info" contact to avoid sending mixed signals to the body. See image below from Dimitrov's K-mount site:




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04-09-2015, 12:29 PM   #11
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I had same problem last week with plastic mount cosina zoom, did fix with about cheapest copper foil tape found in ebay. But in ur case cos mount is metal I do scratch black paint off, no need to play with tapes.
04-09-2015, 12:42 PM   #12
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QuoteOriginally posted by stevebrot Quote
You should only short the "data/digital info" contact to avoid sending mixed signals to the body.
Thanks Steve, you've saved me a lot of research. I was just about to look into what each of the pins were for, so I could isolate the relevant one(s)!!

---------- Post added 04-09-2015 at 08:52 PM ----------

QuoteOriginally posted by stevebrot Quote
You should only short the "data/digital info" contact to avoid sending mixed signals to the body.
Just thinking a bit more on that... Surely when an all-manual lens is fitted where the mount isn't painted, all the pins would be shorted anyway? Or am I being dumb (entirely possible / probable!!)?

---------- Post added 04-09-2015 at 08:56 PM ----------

QuoteOriginally posted by Joojoo2010 Quote
I had same problem last week with plastic mount cosina zoom, did fix with about cheapest copper foil tape found in ebay. But in ur case cos mount is metal I do scratch black paint off, no need to play with tapes.
Thanks. I've found some tape on eBay that is just 38 microns thick and very inexpensive, so have ordered a small amount of that. Hopefully it's thin enough that it shouldn't cause much additional friction, if any. For me, this is preferable to scraping paint off, as I'd like to keep this and any similar lenses in original condition...
04-09-2015, 01:14 PM   #13
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Yeah, I've just covered the whole area (where the pins would be) -- no problem. Possibly, if you only did it half way or something it might get confused (in which case I guess it would display an aperture, maybe even try to stop down in a mode other than "M"?). I found if I tried to put a tiny piece of tape in one area it would just fall off (sometimes into the lens) so I prefer bigger pieces. (Having the tape go up the side of the lens a little might be a option with some lenses.)
04-09-2015, 04:19 PM   #14
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QuoteOriginally posted by BigMackCam Quote
Surely when an all-manual lens is fitted where the mount isn't painted, all the pins would be shorted anyway?
Yes, that is true with the exception of the "A" contact. At least that is how it is supposed to work.* The clue is if you see something other that F--- on the LCD for aperture.


Steve

* I have a Soviet-made M-42 lens (Jupiter-9) that has a painted base that is mildly conductive. Would you believe that the camera sometimes thinks that an "A" contact lens is mounted despite the "A" contact being recessed and nowhere near the lens mount flange?


Steve
04-10-2015, 07:02 AM   #15
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QuoteOriginally posted by stevebrot Quote
Yes, that is true with the exception of the "A" contact. At least that is how it is supposed to work.* The clue is if you see something other that F--- on the LCD for aperture.


Steve

* I have a Soviet-made M-42 lens (Jupiter-9) that has a painted base that is mildly conductive. Would you believe that the camera sometimes thinks that an "A" contact lens is mounted despite the "A" contact being recessed and nowhere near the lens mount flange?


Steve
Interesting... a capacitive coupling effect, maybe? Can you still use the lens in M and Av modes (by setting the camera to an arbitrary F-stop and using the green button / DOF preview to meter)? I have a Helios 44m 2/58 that I'm in love with, but the extra reach of the Jupiter 9 would be useful... and I have no primes to slot between my 58mm and 135mm
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