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01-21-2010, 03:12 PM   #1
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Sigma 24-70mm F2.8 EX - K10D aperture problems

Hi,

I recently bought the Sigma 24-70mm F/2.8 EX DG as a walkaround lens and I am soon going on a trip abroad where I planned to use it a lot. However it seems my K10D has problems to set the aperture, sometimes the top-display says "F--" as if it were a manual aperture lens.

I searched for similar problems on the web and found a post right here with the K10D and the same Sigma, and one of the tips were to use some tinfoil on the third pin to force the camera to believe it's an "A" lens, which works fine for me (but not for the person in the other post).

But it's a brand new lens, it should work out of the box, and I don't want to do the tinfoil thing since it will make some of my older manual lenses appear as auto-lenses and mess with the metering. And since I'm going on the trip for a month soon, I don't want to send the lens away either.

So my question to all you Pentax gurus is, is there a way to fix this more permanently by myself? Can i somehow extend one of the pins (camera or lens) and make it work with the Sigma AND older lenses still being treated as manual? Or is there another way to solve this?

I'd be grateful for any tips and if you need more details just ask! If someone can see anything in it I also attach a photo of the lens' pins.

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01-21-2010, 04:06 PM   #2
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If it is a brand new lens you should send it back and don;t mess with it at all

it does have a warranty
01-22-2010, 04:51 AM   #3
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Yes I know, but the problem is that I'm going on a trip to Asia soon, and I probably wont get the lens back before that, so I wanted to see if anyone knows of an easy fix so I wouldn't have to return it. It's also bought from Germany while I live in Sweden so the shipping will take some extra time, but I don't know, perhaps the Swedish service point (if there is one) also can handle it. Either way, thanks for the suggestion.
01-22-2010, 06:25 AM   #4
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it sounds like one of 2 things

bad connection / allignment of the pin in the sigma lens, or a bad contact of the A position.

try putting the lens in and out of A with the aperture ring and also try rotating the lens back and fourth when locked in place, there will be a little play


you may find either one fixes the problem

01-22-2010, 03:53 PM   #5
axl
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I had different Sigma lens (24/2.8 Super Wide II AF) which had the same problem. Some times it was OK, sometimes it the camera couldn't recognise/set/operat the apreture. I sold it (not here on the forums - to keep my record clean).
I'd second to Lowell's opinion. It's either bad A contact or problem with apreture ring. My lens usually came to it's senses after I dismounted/remounted it. Sometimes even turning camera on/off would help. Anyway, my lens was some 15 odd years old, if yours is new, it's unacceptable so just return it.

BR
Peter
10-25-2011, 04:05 PM   #6
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Sorry for bumping this thread but I realized I hadn't posted what I did, and I thought that in case anyone else finds it and has a similar problem, he/she would appreciate a solution (at least what worked for me).

As suggested, it sometimes worked if I held the lens tighter towards the body so it seemed like a loose pin or something similar, and the tinfoil trick worked. But I didn't want a permanent tinfoil on the body since it would cause the body to believe all lenses are A lenses...so I took my chances and disassembled part of it to attach the "tinfoil" inside the lens instead, at the problematic pin.

Not a clever thing to do, start with a modern AF zoom when one has never opened a lens before or worked with anything similar, but I was young and foolish =) (a year or two younger anyway). In the process I dropped a small metal part, that I still don't know where it goes, and afterwards I temporarily got lost temporarily unable to reassemble it, but in the end I managed to solder a tiny wire to the pin that would "ground" it, or at least connect it to the metal mount, which would have the same effect as the tinfoil, and after some effort put it back together, except for the small metal part.

It all worked well, or so I think, but there has been one issue. I never really thought the lens to be very good, at least when not stopped down to 6 or so, in spite of some relatively good reviews. But sometimes it would surprise me and give me excellent shots even not very stopped down. I wasn't very experienced at the time (and compared to some I'm still not) so I never checked how well it focused but went on using it. Recently I got a K5 and DA12-24 and my wife got to play with my K20 and this lens on a trip, and one time she couldn't get a focused shot of me a few meters in front of her any way she tried, even through numerous tips from me. At first I thought that she hasn't been using DSLR a lot so some soft images are to be expected, but this one was more than that so I tried myself and it seems we found one of the weaker zoom/distance combinations of the focus problem, because it was badly overshooting when autofocusing in any way. So I read a bit about the focus adjustment menu and now it's as good as new! To bad it took a year or two to find it though so now I'm going to check all my AF-lenses (just a couple more =) ).

Now I'm not sure if it was the reassembly of the lens and I'm to blame, or if it was the Sigma QC, or simply bad luck, but I guess one lesson to be learned is that when buying lenses for a specific occasion, do it a while before so you can sort out any problems sensibly instead of doing the panic-mecanic =).
10-28-2011, 08:08 PM   #7
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Respectfully, I have to say the other lesson is it's not worth ruining a lens under warranty without considering other alternatives (which you didn't mention so I can only assume were not considered) - i.e. renting a lens for the trip, borrowing one from a friend, or purchasing another as an exchange from the store (if possible) and you ship back the bad copy for credit.

At this point, your one option is to send it back to Sigma for repairs and hope the repair bill isn't close to the cost of a new lens.

Best of luck!
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