Jupiter 21m Lens Problems

I recently bought a Jupiter 21m from ebay and got totally ripped off by the seller who had described the lens as far more functional than it actually was. As it would have cost me way too much to post back for a refund and because I am never one to give up on something, I decided to take the lens apart and repair it myself.

All is well and good and I have taken the lens fully apart into well over 70 component parts and already traced and fixed two of the problems with it. The trouble is, now that I am down to the aperture and have removed and taken it apart and reassembled it, I have discovered rather much to my dismay that despite the fact that it refuses to work, there appears to be absolutely nothing wrong with it!!

What I would like to know is if anyone else own this lens and if so, whether the apertures on them are particularly bad. Mine closes with an uneven star-like shape which, as it shrinks, becomes an slightly lopsided octagon. I cannot make it function any differently despite the fact that there is no damage to the fins or any other part of the mechanism. It seems like microscopic variances in the wearing of the parts, particularly the metal tracks are being amplified by the movement of the fins and leading to this uneven closing.

If they are all like this, I won't bother buying another. I will just put it back together and mainly shoot wide open with it.

Any advice on aperture repair or any stories of good or bad experiences with this particular Russian lens would be greatly appreciated.

Thanks. :-)

I don't know the Jupiter 21m, but on some lenses it would be possible to assemble the diaphragm with the blades the wrong way round - i.e. with the pins that should go in the holes actually in the slots, and the pins that should go in the slots actually in the holes. I would imagine this could cause the type of effect you are describing. Could this have happened?

Steve.

Hmmmm, That's an interesting thought. Thanks for your input. :-) I don't thinks it's possible on this model but I'll double check that and report back. It generally works, it's just kind of wonky. I'll let you know how I go with that.

No. :-( I'm afraid that isn't the issue. But thanks heaps for the idea, Steve. The fins CAN be installed the other way around with the opposite pins in holes but this causes two whole different issues. 1. The aperture can never be fully opened and 2. worse still the 'slot plate' for want of a better name cannot be fitted with the fins in this inverted position. Back to the drawing board I guess... :-(

Sorry that idea didn't work out. I must admit I hadn't given full consideration to the "lop-sided" effect, and was concentrating on the "star-like shape"!

The [url="http://www.ussrphoto.com/Wiki/default.asp?WikiCatID=26&ParentID=2&ContentID=800&Item=Jupiter-21+M"]Wiki page for the 21m[/url] shows 2 lenses with the apertures wide open, which look completely normal, and if you look at eBay item [url="http://www.ebay.co.uk/itm/Jupiter-21M-4-200-TELE-Lens-M42-Pentax-Zenit-/320940387630"]320940387630[/url] there is a picture of the aperture closed, showing a nice symmetrical octagon. Yours presumably looks the same, but lop-sided.

An 8-bladed diaphragm isn't going to be perfectly circular, except wide open, but "star-like" doesn't sound right. I hope someone with the same lens can give you clearer advice.