How to repair aperture of Sigma 18/2.8 (m42)

vulko

I just got M42 Sigma 18mm/2.8. The aperture wouldn't close from f8, and the blades seem to make not a perfect 6-angle figure.

Tried to repair it by myself, but I wouldn't get any further then the blades. It seems like mechanism is deeper inside the body, as I have no experience dont want to disassemble the whole lens.

Does anybody have any exp. on the topic? I would rly appreciate if you give me some advice how to fix it.

cooltouch · Joined: 15 Jan 2009 Posts: 9097 Location: Houston, Texas

I've never been into a Sigma 18mm before, so I can't offer any advice. But you may try posting a note over at the KY Photo Classic Camera repair forum. There are some very knowledgeable folks who frequent that forum.

http://www.kyphoto.com/cgi-bin/forum/discus.cgi

WolverineX · Posted: Fri Aug 06, 2010 9:47 pm Post subject:

can you post some photos of the lenses, front ant back, and disassembled as far as you got?

vulko · Posted: Sat Aug 07, 2010 7:41 pm Post subject:

cooltouch,
tnx for the link, I'll try to ask there.

WolverineX,
well I disassembled the rear part (metal ring) and unscrewed the rear lens, below which I found apperture blades. Yet to get to the mechanism I need to get deeper inside the lens. The thing is, this lens has a ring, when you turn it there is 4 types of filter (1a, blue, orange, yellow) located inside the lens. And they are changed by turning this ring. Never seen anything like this and I don't want to break this filter changing mechanism, which can be located very near to the apperture. Thats the problem.

WolverineX · Posted: Sat Aug 07, 2010 8:18 pm Post subject:

that's filtermatic system, i have sigma 8mm filtermatic fisheye, but in case of my lens i can remove top part of the lens to get to the filter and change it...

back to your lens, you can open and close the aperture blades from f2.8 to f8 but not further? that sounds to me like blades are out of alignement so one of the blades blocks others preventing the closing of the iris, you will probably have to remove them and set them anew...you will have to get to the aperture through the front of the lens...

as i mentioned in previous post, it would be good for you to take photos of the lens and post them here, so we can get some idea what are we dealing with here, and that way we can help you

vulko · Posted: Tue Aug 10, 2010 8:18 pm Post subject:

I did it.

Many thanx to Wolverinex, you were right.

Dissasembled the whole lens, and assembled it again. But now apperture fully working Smile

A lot of useless work I did, but for the first time repairing a lens I think its ok.

clie · Joined: 18 Sep 2014 Posts: 5

can you post how you managed to disassemble the lens?

I have a Sigma XQ Filtermatic 24mm f2.8 and I'm trying to get inside to remove a piece of hair! It is located between the front 3rd element and the last front element (just before the blades). I managed to remove the first two elements easily. But don't know what to do after that to remove the 3rd element.

WolverineX