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02-20-2011, 09:40 AM   #1
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Odd problem with Sigma Mini-Wide II and K10d

A few weeks ago I purchased a Sigma Mini-Wide II 28 f2.8 in excellent shape.

Yesterday when I was using it I noticed that in AV mode the lens would not open up to 2.8, in the top LCD it would only go to 4.0, but would go all the way up to f32. (the lens is only an f22)

Since the lens has the "A" setting it should open all the way up in AV, and it did for the first couple of weeks.

If I use the aperture ring it will open to 2.8, (I took test photos, checking shutter speeds and exposure) Also, in "M" mode on the camera, the lens acts the same way, going from f4 to f32.

Any ideas?

02-20-2011, 09:42 AM   #2
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Sounds like dirty contacts. Clean them with isopropyl alcohol and see.
02-20-2011, 11:12 AM   #3
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QuoteOriginally posted by wlachan Quote
Sounds like dirty contacts. Clean them with isopropyl alcohol and see.
In M mode using the aperture ring manually? What do the contacts have to do with that?

02-20-2011, 01:16 PM   #4
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That's the same symptom some Tamron PK-A Adaptall mounts suffer...only opening to f/4.

Check the contact pins on both the camera and lens. There may be some junk on them since the lens worked initially. Clean them. It may require you to "finesse" the lens once it's mounted to get the lens to go wide open...in other words, wiggle it

02-20-2011, 05:32 PM   #5
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It has to be contacts. If you look at the contact decoder chart on this page, notice that changing the contact pattern from 011*10 (f2.8-f22) to 010*10 tells the camera the lens aperture range is f4-f32, exactly the symptoms described.

My 24mm Super-Wide II does the same thing sometimes. This crappy photo (mine) isn't quite good enough to show the problem. I think Sigma used a generic mount with holes drilled for all the possible codes for their lenses. Then they used nylon plugs for zeroes and brass plugs for ones. The brass seems to get dirty quickly. I use a pencil eraser on mine.

02-20-2011, 07:12 PM   #6
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Original Poster
Thank you everyone.
Cleaning the mount with alcohol did the trick. (funny that they looked very clean before)

Again, thank you
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