Aperture issue with 1992 Sigma 28-70 f/2.8 (only works properly at 2.8)

Hydrblades

EOS 90D
Jul 30, 2022
2
1
Hey guys,
I have a "little“ problem with my Sigma 28-70 f/2.8 (the 1992 model, very old I know but I got it for free so why not (try) use it): whenever I want to take a photo with this lens at another aperture than 2.8, I get Err. 1 message (‘clean lens contacts and restart camera’). However, as long as I take photos at 2.8, it works perfectly fine. No errors.
But now it comes to the strange part (which doesn’t make sense to me): first of all, while filming, there is absolutely no problem if I use other apertures than 2.8, the camera continues to film as if the lens would work perfectly fine. Secondly, if I take photos with an aperture of more than 2.8, I get the error shown on the screen, but only while the camera is saving the photo I just took. After the photo is saved, it takes another maybe 5 secs, but then I can continue shooting (no restart of the camera needed). Of course in practice this is pretty annoying and very inefficient. I also need to underexpose the photo at about -2ev, no matter what shutter speed I use.

I already tried cleaning the contacts on the lens as the error message suggests, but ofc it didn’t help (which I honestly didn’t expected to do but yeah, still tried it). My friend, from whom I got this lens, has the same problem with the lens on his M50 (using the EF-M adapter obviously). I thought that maybe the adapter is the problem, but nope it’s not.
So I was wondering if anyone knows a solution to this problem (even though I suspect this to be a mechanical problem…)? And more importantly, is there any chance the lens could damage my camera in any way if I continue using it?

And yes, I know, this lens is pretty old and even if it would be possible, having it repaired wouldn’t make sense, but until I can afford a newer 2.8 lens I’d like to use this one since it’s my only lens besides the kit lens.
Thanks in advance and have a wonderful day/evening or whatever
 

dlee13

Canon EOS R6
May 13, 2014
302
195
Australia
Might not help but to me this sounds like a stuck aperture. I had a friend with a Sigma lens that you could shoot at any aperture in the camera but the physical aperture rings would not move. This lens was only 2-3 years old too and the cost of repair was almost the same as a brand new one.
 
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Hydrblades

EOS 90D
Jul 30, 2022
2
1
Might not help but to me this sounds like a stuck aperture. I had a friend with a Sigma lens that you could shoot at any aperture in the camera but the physical aperture rings would not move. This lens was only 2-3 years old too and the cost of repair was almost the same as a brand new one.
Thanks a lot!
I just checked if that's the case for me as well - and it is. Or at least I don't see the aperture closing when I adjust it.
This also explains why my pictures are all overexposed when I try shooting with a lower aperture.
 
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dlee13

Canon EOS R6
May 13, 2014
302
195
Australia
Thanks a lot!
I just checked if that's the case for me as well - and it is. Or at least I don't see the aperture closing when I adjust it.
This also explains why my pictures are all overexposed when I try shooting with a lower aperture.
No problem and I believe you won’t see it closing as Canon use stop down focusing so the lens always stays wide open and only closes the aperture as the photo is taken, that gets as much light as possible when taking photos to help AF.

But if you are keeping the ISO/SS the same but the exposure is always off when changing aperture then a stuck aperture is most likely.