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09-13-2012, 03:09 AM   #1
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Broken aperture blade guiding pins

Hi, about a week ago I received an old pre-set Cunor 400mm f6.3 lens. I took a few test shots with it while at work, planning to do more serious testing this weekend, as I was very happy with the initial results. Yesterday a friend came by and I showed him my "new" pre-set lens. He didn't know how it worked and while I explained to him, he started fiddling with it. About an hour after he left, I decided to take another few shots, and all of a sudden the aperture, which previously worked fine, started acting up. I decided to open it up, and found that 7 of the 15 blades aperture guide pins were broken off completely. I guess my friend forced the aperture past the pre-set range, doing the damage.

Can anyone tell me how to fix the blades, I thought of gluing the pins back to the blades, but don't think it'll work, or perhaps another alternative is removing the broken blades and spacing the good blades into every second guide. If that won't work I'll remove all the blades and be stuck shooting wide open all the time.

Another lesson learned the hard way, never let anyone fiddle with your lenses

EDIT: If I remove the blades completely, would the aperture diameter be a little bigger / How would I calculate the new aperture?


Last edited by altopiet; 09-14-2012 at 04:44 AM.
09-13-2012, 03:55 AM   #2
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If you can't fix it, it looks as though it would serve as a suitable weapon against the person who broke it.
09-13-2012, 05:03 AM   #3
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QuoteOriginally posted by elliott Quote
If you can't fix it, it looks as though it would serve as a suitable weapon against the person who broke it.
I'll tell you, the lens is really heavy, if I hit him with it I'm sure I'll kill him
09-13-2012, 06:24 AM   #4
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A shot taken with the blades removed, with mono pod from about 50m away

1. No pp, resized from RAW to JPEG



2. 1. with minimal contrast and sharpening PP



The lens



Last edited by altopiet; 09-13-2012 at 06:37 AM.
09-14-2012, 10:50 AM   #5
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the ability to repair depends on your patience (it needs to be extreme) and your ability to do fine work.

I had a preset macro lens (on a bellows) that was made by soligor. the mechanism did not use pins, but had simply punched holes, where the drag through of the punching is what rode in the aperture control slots

as the punching wears these can skip.

some of my aperture blades were even bent.

what I did, was to take some copper house wire and stretch it straight (pliers and vice and just pull on the wire) and used this to make pins.

you need to epoxy the pins in, and then sand the back of the pins perfectly smooth, as the blades must pass them freely (which is why they used the punch method) and then cut / sand the other side of the pin to a small but uniform length.

mine worked reasoably well, but in the end the blade caught part of the back of a pin, and bent.

note to straighten aperture blades, the best way is to peen them. (literally with a hammer avoiding the pins) against a steel block it willl take you several hours to fix.
09-14-2012, 10:17 PM   #6
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Thanks for the reply Lowell. I'm lucky that I found all the pins on the inside of the lens, and only 3 of the blades are a little bent at the end where the pins popped out. I've done a few lens repairs, but this is very fine and detailed work, and my eyes are not that good anymore. What about the easier option of re-spacing the remaining blades to every second guide. I know that it will have an effect on bokeh, but it would still allow me to stop down, wouldn't it? On the other hand, seeing the IQ wide open, which isn't too bad, perhaps I should just leave it with the blades removed if re-spacing won't work?
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