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02-10-2007, 04:45 AM   #1
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Sigma/Pentax lens problem

I bought a new Sigma 50mm 2.8 EX DG macro lens (for Pentax) and attached it to my K100D camera and have the following problems:
1. Am not able to change aperture or even register an aperture on the viewfinder screen while using AV mode.
2. The lens dramatically over-exposes with flash.
3. The colors are much too blue and unnatural even after adjusting white balance in P mode.
When I switch back to my 18-55 kit lens everything works fine. Any suggestions? Freddy

02-10-2007, 05:25 AM   #2
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Hm, the first two problems sound like you don't have the aperture ring of the Sigma 50 in the "A" position - I don't know, but suspect that the Sigma has an aperture ring. If this is so try to set the aperture ring to "A" and see if the first two problems aren't gone afterwards.

Else try to clean all contacts of the Sigma thoroughly - maybe the contacts have some residue and can't transmit the aperture information correctly.

Third option would be that you got a faulty lens.

Don't know how I could help you on the third problem though - if you used both lenses with flash and experienced such dramatic color shifts I really am amazed ...

Phil
02-10-2007, 06:36 AM   #3
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might be a faulty lens. return it to where u got it, or call up sigma and send it out to long island and get it fixed.

i had a faulty lens recently, not similar problems, but problematic enough..
call up their tech support

my lens had a bad wafer board, or something like that. works great now...
02-10-2007, 06:44 AM   #4
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sounds to me that u dont have the aperture ring in the A position..

its not unsual to have to lower the flash power compared to the kit lens mine needs a minus 1.5 i think..

trog

02-10-2007, 07:13 AM   #5
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Well, I'll be darned, Phil. I didn't have aperture ring at A . Now that I've done so I am shooting with flash, indoors in automatic (auto pict) and the color is fine. But whatever I try to focus looks blurry in the viewfinder and when I try to shoot in P mode or even auto pict outdoors from 3 feet to six feet to beyond my pictures are extremely dark. Could it have to do with exposure (don't see how if I reset the camera and shoot in automatic). The six foot picture info on the six foot shot on terrace (no flash) reads : 1/2000 f4.0 -1.5ev , iso 200, automatic white balance. Is this info helpful? Look forward to your reply. Thanks, Freddy.
02-10-2007, 07:20 AM   #6
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-1.5 EV ???????????????? Start w/ Zero
02-10-2007, 07:32 AM   #7
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QuoteOriginally posted by fevbusch Quote
Well, I'll be darned, Phil. I didn't have aperture ring at A . Now that I've done so I am shooting with flash, indoors in automatic (auto pict) and the color is fine. But whatever I try to focus looks blurry in the viewfinder and when I try to shoot in P mode or even auto pict outdoors from 3 feet to six feet to beyond my pictures are extremely dark. Could it have to do with exposure (don't see how if I reset the camera and shoot in automatic). The six foot picture info on the six foot shot on terrace (no flash) reads : 1/2000 f4.0 -1.5ev , iso 200, automatic white balance. Is this info helpful? Look forward to your reply. Thanks, Freddy.
"-1.5ev" that is why your photos are dark. You set exposure compensation to underexpose (darken) your photos by one and a half stops.

If things look blurry in the viewfinder check to make sure your AF is set correctly.
02-10-2007, 07:38 AM   #8
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Hi Freddy, somehow in all your working with camera settings etc, you managed to set the exposure value to -1.5. That means the camera thinks you want to take the picture 1.5 fstops darker than what the meter is reading. Reset the EV to 0 and you should be fine. Don't feel bad I've done that myself. Or even worse set it intentionally and then forgot to reset it to zero and happily underexposed over 90 shots :cries: That was in the days before I learned to check exposure in the lcd.

NaCl(stupid cameras always do what I tell them to do even if it's wrong)H2O

02-10-2007, 08:33 AM   #9
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QuoteQuote:
Reset the EV to 0 and you should be fine. Don't feel bad I've done that myself. Or even worse set it intentionally and then forgot to reset it to zero and happily underexposed over 90 shots :cries: That was in the days before I learned to check exposure in the lcd.
Me, too, but only -0.5, for about 30 shots. Nice dark blue sky, though.
02-10-2007, 08:51 AM   #10
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I don't know how to thank all you guys. You're all like Superguys coming to the rescue. I straightened out the exposure setting to 00.00 and 0.5. One of them is the right one, I think. But at least I know what I'm doing now.
This lens is remarkable (Sigma 50mm 2.8 eX DG). I attached an image I just took with it. I think I'm in love! Hope you can see the image okay. Thanks again, Freddy.

Last edited by fevbusch; 02-22-2007 at 12:55 PM.
02-10-2007, 08:55 AM   #11
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0 is the default.. but u might have to alter it sligthtly with different lens makes. also bear in mind that if u have any plus or minus ev set the neat auto iso feature will stop working and default to iso 200 on the k100d..

to use the in-camera flash i am pretty certain u will have to turn the flash power down in the menue as well.. set your camera till the pictures come out as u want them..

trog
02-10-2007, 09:01 AM   #12
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an example useing your pic freddy.. if your auto iso goes up to say 800 as it would and it all comes out correctly.. dialing in any plus or minus ev will drop the iso to 200 and u will get black land..

major bug..

trog
02-10-2007, 09:03 AM   #13
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Will do. Thanks, Trog. Freddy
02-10-2007, 11:24 AM   #14
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Trog, thanks. That's a biggy for my knowledge base. (The thing about the
+ or minus ev affecting the iso). Freddy
02-10-2007, 12:00 PM   #15
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it just wrecks the auo iso feature.. it wont alter the iso if its fixed manually..

i find the ev button serves two main purposes.. the ability to adjust the odd pic u think needs it..

and the ability to put in what i would call lens bias.. some lenses are correct with the camera default 0 setting.. some.. the sigma u have being one of them have a tendancy to over expose at the 0 setting.. dialing in a permanent minus ev with such a lens means u no longer have the auto iso function..

u will also need to set the flash power in the menue lower to avoid over exposure when u use the cameras in-built flash..

why all this is i dont know.. he he he

trog
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