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01-10-2013, 02:52 AM   #1
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Auto Chinon 1:1.7 f=55mm Lens stuck wide open

Hi Guys,

I started getting interested in photography on my birthday last April. I quickly realised that it was going to cost a lot of money to get good "glass" so began to explore the world of vintage lenses (and m42 in particular).

I bought several and most were great and have really pushed up my skill levels, being forced to use the M mode.

However, one of the lenses I purchased is the Auto Chinon 1:1.7 f=55mm Lens and it appears to be stuck wide open.

There is an "Auto/Manual" slider switch on the back and pushing it to manual doesn't help.

Can it be rescued? Will I have to take it apart? Should it be thrown in the bin?

Thanks in advance.

01-10-2013, 04:47 AM   #2
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What do you mean stuck? Does the camera never stop it down, or is it impossible to change aperture even off-camera?
m42 lenses are usually not too hard to take apart, so you can try to fix it, but you still need some tools and diagrams. And I don't think lenses should ever be thrown in the bid, there is always someone who can use it, even if just for parts.
01-10-2013, 05:39 AM   #3
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Send it to me
01-10-2013, 11:52 AM   #4
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QuoteOriginally posted by Na Horuk Quote
What do you mean stuck? Does the camera never stop it down, or is it impossible to change aperture even off-camera?
m42 lenses are usually not too hard to take apart, so you can try to fix it, but you still need some tools and diagrams. And I don't think lenses should ever be thrown in the bid, there is always someone who can use it, even if just for parts.
I'm using a Canon 40D so the stopping down has to be done manually. The aperture is wide open, even off camera.

How would I get the diagrams, I have some small tools which should be able to get it open.

kcobain1992 - what's your address

01-10-2013, 12:15 PM   #5
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You could try using these instructions, however the method used is very crude. Lenses don't require diagrams generally. It seems that you will need a lens spanner, or callipers of some sort. The front ring comes off spinning it counterclockwise, with a friction tool (an M42 rear cap with some rubber, like from a balloon, should work perfectly). If you don't have these tools, I'd say either invest in them and also keep them for later, or pass the lens to somebody who has them, and pick a better copy next time. Do not, under any circumstance, drill holes in it.
01-10-2013, 12:28 PM   #6
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QuoteOriginally posted by kcobain1992 Quote
Do under any circumstance, drill holes in it.
^How your average inexperienced "Repairman" views that statement.
01-10-2013, 01:38 PM   #7
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Thanks for the instructions.

My guess is that I'd have to go in through the back.

Would there be screws to tighten inside to fix the problem do you think?
01-10-2013, 01:43 PM - 1 Like   #8
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Not really, no. Usually, there's the optical block which contains the aperture leaves, and has a protruding lever which connects to an F shaped lever on the mount part. So when you press the silver pin on the rear, the movement translates into sliding the F-shaped lever, which closes the aperture. Something along that way is impeding movement, however you have to see exactly what it is. It could be the mechanism in the mount part, composed of springs and levers, it could be the lever of the optical block, or it could be that grease has spread inside the optical block, and made the diaphragm blades stick together. Most certainly it's the latter, so you'll have to close the aperture somehow, remove the lens elements and put them somewhere safe, and repeatedly clean the blades with some lighter fluid or any other de-greasing substance, until they're clean and dry.

01-10-2013, 02:26 PM   #9
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Thanks, I'll let you know how I get on.
01-10-2013, 04:56 PM   #10
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Btw, make sure you have a good space to do this. You dont want dust to get in there when its open. I read that there is a big problem with even particles of skin, like tiny dandruff, falling in. Not sure whether the posters were just paranoid, though
01-10-2013, 05:02 PM   #11
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I just had a look inside and I don't think I'm going to be able to fix it. Thanks for all the help guys, but I'll just sell it for parts.
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