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03-25-2013, 10:42 AM   #1
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Sigma Super Wide II reporting 1 stop slow

I recently bought a used Sigma Super Wide II 24mm f/2.8 for a pretty good price. It works perfectly except for one small problem.

Although it's a somewhat old MF lens, it does have an A setting. The problem is that the lens is telling the camera it's one stop slower than reality. The camera says the fastest setting is f/4, and it stays consistently one stop slower all the way to minimum apeture. I have confirmed by using the apeture ring and stop-down metering that, in A mode, f/4=f/2.8, f/5.6=f/4, f/8=f/5.6, etc.

It's workable, but my EXIF will always be incorrect. I have tested with both my K-r and K-5 IIs, so it's not the camera.

I am thoroughly confused right now. Anybody have a similar issue on their lens? Any lens at all?

03-25-2013, 10:56 AM   #2
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Someone may have done a repair and replaced the internal circuity with one from a different lens.

I accidentally did that previously when I fixed a non working A Sigma telephoto.

I used the back end from a cheap Sigma zoom as a replacement and the lens subsequently reported apertures one stop faster than actual. I did get the A mode working again though.
03-25-2013, 10:58 AM   #3
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QuoteOriginally posted by scratchpaddy Quote
I recently bought a used Sigma Super Wide II 24mm f/2.8 for a pretty good price. It works perfectly except for one small problem.

Although it's a somewhat old MF lens, it does have an A setting. The problem is that the lens is telling the camera it's one stop slower than reality. The camera says the fastest setting is f/4, and it stays consistently one stop slower all the way to minimum apeture. I have confirmed by using the apeture ring and stop-down metering that, in A mode, f/4=f/2.8, f/5.6=f/4, f/8=f/5.6, etc.

It's workable, but my EXIF will always be incorrect. I have tested with both my K-r and K-5 IIs, so it's not the camera.

I am thoroughly confused right now. Anybody have a similar issue on their lens? Any lens at all?
Mine does the same thing as the temperature changes. When it is cold, it is f/2.8, but when it gets warm it goes to f/4. One of the contacts that tells the body the aperture is slightly recessed -- doesn't seem to always make contact. A tiny piece of conductive foil tape solves the problem. To see why this is so, look at this page:

http://www.robertstech.com/matrix.htm
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03-25-2013, 11:15 AM   #4
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QuoteOriginally posted by vonBaloney Quote
When it is cold, it is f/2.8, but when it gets warm it goes to f/4.
I bet that's the problem I have with mine. It's never been cold since I bought it . How cold is "cold" for your lens? I've heard it gets pretty cold in Colorado. Not Canada cold, but cold for someone from Georgia, like me.

It's strange that I've never seen anyone mention this problem before. I'll try your foil fix when I get home. I'll check the screws for tampering evidence, too, in case crewl1 is right. They always get stripped a bit when people take stuff apart. At least, they do when I take stuff apart.

03-25-2013, 11:37 AM   #5
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QuoteOriginally posted by scratchpaddy Quote
I bet that's the problem I have with mine. It's never been cold since I bought it . How cold is "cold" for your lens? I've heard it gets pretty cold in Colorado. Not Canada cold, but cold for someone from Georgia, like me.

It's strange that I've never seen anyone mention this problem before. I'll try your foil fix when I get home. I'll check the screws for tampering evidence, too, in case crewl1 is right. They always get stripped a bit when people take stuff apart. At least, they do when I take stuff apart.
I'm sure it is just a lens-to-lens thing. Sigma quality control back then was very iffy, even though they did make some nice lenses.

Cold is any temperature in the winter and early spring (indoors or out) -- up to maybe mid-70s. Hot is summertime -- 80s and up, or direct sun heating the thing up. Originally I just thought it was randomly flaky, but then noticed I would check it in the morning and it would be fine, and then I'd take it out in the heat of the day and it would read f/4. This same lens got really cold one time and the aperture lever actually bent and kept the aperture from fully opening. I had to open up the mount and unbend it. So whatever metals they were using at the time seem very prone to expansion/contraction with temperature causing weird side effects. It is very sharp though, so I deal with it...
03-25-2013, 11:42 AM   #6
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do not feel bad I have a 100-300mm lens that thinks its a 70-200mm f-2.8 lens wish it was LOL
03-27-2013, 11:19 PM   #7
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Features and Operation of the Ka Mount
It looks like the lens is dirty or not connecting / shorting the R2 position to the lens mount
03-28-2013, 02:30 AM   #8
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Don't worry, my cameras just report it's an A series lens, it doesn't have a clue which one, unless I tell it.

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