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11-16-2009, 01:12 PM   #1
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Dark pictures sometimes on K20D. pics added

Hello everyone. I used my K20D this summer quite a bit shooting motorcycle races. On the very last day of the races I noticed that every so often I would get a black/very very underexposed image. The image before and after the black/very very underexposed image was fine. These shots were taken within 10-20 seconds from the first to the last shot. When I got home I was able to brighten them up and take the noise out but the shot was basically lost. Has anyone else had this problem? I was using the Sigma 50-500mm with a 8 gig memory card (sorry I don't remember which brand), ISO was probably on 400 or 800 I think. When I get home I will post that shots in order without any postproduction other than resizing them. I'm just wondering with the race season over should I maybe send it to Pentax and let them go over it to see if something might be getting ready to go on the blink. Because races start in only 5 months and I want to be ready for them .

Thanks
Jim


Last edited by jbrowning; 11-16-2009 at 05:41 PM.
11-16-2009, 01:59 PM   #2
Ash
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G'day Jim.
It would be most helpful if the images or at least the EXIF data on the shots (along with that of the shots that did work) were posted to work out where the issue lies.

Doesn't sound like normal behaviour but there's just too many possibilities without knowing the full story.
11-16-2009, 02:51 PM   #3
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QuoteOriginally posted by Ash Quote
G'day Jim.
It would be most helpful if the images or at least the EXIF data on the shots (along with that of the shots that did work) were posted to work out where the issue lies.

Doesn't sound like normal behaviour but there's just too many possibilities without knowing the full story.

Thanks Ash, I will get those uploaded when I get home along with the EXIF.

Thanks
Jim
11-16-2009, 05:21 PM   #4
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Here is a link to the three pictures. Sorry I uploaded them here but all the EXIF was taken off.

New Page 2

Thanks
Jim

11-16-2009, 05:54 PM   #5
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I'm just guessing here but looks like an aperture issue? The first and third pic the bikes and grass are never both sharp at the same time (as expected from a supertele), but the second pic the depth of field looks increased, as if it's at f/22

When it happens and you noticed, and the results are repeatable, try retaking the shot at the same shutter speed but a smaller aperture. If the results are the same then....
11-16-2009, 06:12 PM   #6
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Hmm....EXIF identical except for slight change in focal length. I would not have thought spot metering would be the best approach however I can't see it making that kind of difference not to mention that all three are f/8, 1/1000. I vote for wanky equipment and would try to replicate in the backyard under controlled conditions and a second lens. Is it possible for a lens to get confused and when told to close to f/8 at shutter time it goes to f/18 instead? Just a thought.....
11-17-2009, 07:05 AM   #7
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Thanks Andi and Lee. I just remembered that I also had the battery grip on the camera and it was one of the first times using the camera with the grip.

Thanks
Jim
11-17-2009, 07:32 AM   #8
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I used a Bigma with my K20D and Grip over the summer and although the grip can cause some issues I don't think yours is one of them. I don't believe the exif can lie. Two pics pointed in the same general direction with the same shutter, iso and aperture should be about the same exposure. Your subject did not change from the sky to a coal mine. I am interested to know if you can duplicate the problem (same exif, different exposure) with any other lens. Again, I recommend you not use spot metering unless trying to meter a small subject with very different exposure than its surroundings (white bird on dark shore).

11-17-2009, 07:37 AM   #9
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Thanks Lee, I don't think I have ever had this problem since then. And I use the same setup just about every weekend. And I almost always shoot on f8 trying to get more than just the subject in focus. But I will try it again this week and see what the outcome is.

Thanks
Jim
11-17-2009, 08:17 AM   #10
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As Andi Lo and imtheguy noted the increased dof but with identical exif, I think the obvious conclusion is a defective lens aperture mechanism.
11-18-2009, 03:14 PM   #11
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This is just a guess, but after a full day of shooting, I would suspect that your batteries might be starting to run out of juice. You didn't say how many pictures you took, but focusing that big a lens must be a drain on the power supply. If the batteries are given just a short recovery time, they will probably work for a time, but short cycle times will demand more power than a dying battery can supply.

It would be worth changing batteries if you see it again.
11-18-2009, 04:28 PM   #12
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It's just my guess, but pic #2 has some very strong highlights coming off the cowling of the bikes which probably threw your metering awry.

Were you center/spot metering?

QuoteOriginally posted by jbrowning Quote
Hello everyone. I used my K20D this summer quite a bit shooting motorcycle races. On the very last day of the races I noticed that every so often I would get a black/very very underexposed image. The image before and after the black/very very underexposed image was fine. These shots were taken within 10-20 seconds from the first to the last shot.
11-18-2009, 05:22 PM   #13
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Hi yes I was using spot metering. I looked at 4 more shots that came out the same way from the same day and all 4 have a glare in the center of the picture. Hmm maybe that was the culprit.

The batteries was charged for at least 8 hours the night before.

Thanks
Jim
11-19-2009, 10:13 AM   #14
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Wrong exif with Sigma lenses?

I was shooting recently at a rowing regatta, straight down from a bridge as the boats came through and got some similar results. I was shooting in burst mode as the bridge was also the finish line and got some very good close-ups of the rowers and thier facial expressions as they crossed the line. After, I noticed every third or fourth shot was dark. Looking at the exif, I found I was also spot metering. I had not changed that setting from earlier when I was shooting from under the bridge because of rain. I was using two different lenses. I initially was using my Sigma 70-300 at 70 mm and found that too long so I switched to the 18-55 kit lens at 55mm and that worked perfectly for the closer distance. I got the dark shots mingled in with both lenses. I was shooting in AV and while the Pentax lens recorded a different shutter speed, 1/250 vs 1/750, the Sigma lens did NOT record any difference in data even though the exposures were obviously different. I understood the exposure difference right off when I discovered I had left the camera in spot metering mode but for whatever reason, the camera did not change the exif data to match the exposure. The exif with the Sigma is wrong. Some of you may think this isn't possible but I have a bunch of shots to prove it. I probably would have started a thread worrying if my camera was broke if I had not changed lenses. The exif with the Pentax lens appears correct. In my case, the lens and the camera worked, it just recorded the wrong information.
11-19-2009, 10:30 AM   #15
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QuoteOriginally posted by reeftool Quote
I was shooting recently at a rowing regatta, straight down from a bridge as the boats came through and got some similar results. I was shooting in burst mode as the bridge was also the finish line and got some very good close-ups of the rowers and thier facial expressions as they crossed the line. After, I noticed every third or fourth shot was dark. Looking at the exif, I found I was also spot metering. I had not changed that setting from earlier when I was shooting from under the bridge because of rain. I was using two different lenses. I initially was using my Sigma 70-300 at 70 mm and found that too long so I switched to the 18-55 kit lens at 55mm and that worked perfectly for the closer distance. I got the dark shots mingled in with both lenses. I was shooting in AV and while the Pentax lens recorded a different shutter speed, 1/250 vs 1/750, the Sigma lens did NOT record any difference in data even though the exposures were obviously different. I understood the exposure difference right off when I discovered I had left the camera in spot metering mode but for whatever reason, the camera did not change the exif data to match the exposure. The exif with the Sigma is wrong. Some of you may think this isn't possible but I have a bunch of shots to prove it. I probably would have started a thread worrying if my camera was broke if I had not changed lenses. The exif with the Pentax lens appears correct. In my case, the lens and the camera worked, it just recorded the wrong information.
When you switched the camera from spot metering mode to something else did you still get the extremely dark shots?

I will try and post the other 4 pictures tonight when I get home if anyone is interested in them.

Thanks
Jim Browning
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