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Old Sep 27, 2006, 9:34 PM   #1
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I was hoping someone could help diagnose something with me. I just got my D80 yesterday, terrific camera so far, tonight I had a chance to take some star shots, I was hoping to be able to pick up the milky way, which it looks like I did. The problem, if it is one, there seems to be a broad vertical band, a bit to the left of center in the picture.

This hasn't appeared in any daytime shots, or in the few sky shots I took at ISO 100.

I haven't seen this in other members shots, it's not something I could see with the naked eye, dose anyone know what this might be a symptom of? Bad lens? Wrong settings? To many 30 second exposures (around 9 of them over about 20 minutes) Something wrong with the camera? Aliens? The shot immediately following this one didn't show this band, but the one after that did. There was 2-3 minutes from the first to the third shot.

I also noticed several stuck pixels but I'm not going to worry about that, at least not tonight, maybe this band isn't something to worry about either for all I know...

Thanks for any suggestions!

John


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Old Sep 27, 2006, 10:13 PM   #2
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I've looked on 3 different monitors (two calibrated) and can't see any bands or stuck pixels. Long exposures can create issues, but this shot looks fine (to me at least)
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Old Sep 27, 2006, 10:53 PM   #3
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Thanks rjseeney, the stuck pixels don't show up on the resized image, but are easily visible as bright red dots at full size - you'd be frightened at how many there are in the test shot with the lens cap on - but since they only seem to be visible at 1600 ISO with long exposures I'm not too worried about that right now.

The band is more concerning, I've looked at these images on 3 monitors and can see it on all three, most obvious on my laptop. 2 have not been calibrated, my wife says she has calibrated hers.

Maybe I'm being to picky, but for some reason it jumped out at me on the images that it showed up on.

Here's another pair of shots, taken back to back. The crop on the left shows the brownish smudge/band running top to bottem very obviously on my screens, the crop on the right only very vaguely shows it, if I didn't see it on the other shots I probably wouldn't have seen it on the right hand shot.

I did some experimenting tonight in PSP X, if I decrease the red channel the mark all but vanishs. Maybe it's just a white balance problem? Could that cause a broad vertical stripe in the same place on several images taken facing different directions?

I'm going to take some more tonight and see if the same thing shows up.

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Old Sep 27, 2006, 11:16 PM   #4
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I have weird purple pixels and streaks if I do a 30s exposure with the lens cap on in the dark and then increase the brightness in picture project (+40).I don't know why there is a pattern.
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Old Sep 28, 2006, 2:32 AM   #5
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looks like a problem with the CCD, I would take it back and exchange it, Since that is noticable (I saw it right away, though my monitor is uncalibrated).

Couldn't be a lens problem or anything, if you can duplicate it then theres a CCD issue, so just take it back. since you just got it it shouldn't be a problem.
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Old Sep 28, 2006, 3:15 AM   #6
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Have you got the Long Exposure noise reduction switched on? The banding is digital noise due to the clocks in the camera. I would have thought that the NR would have eliminated them (not the normal NR - the long exposure NR).

Keith.
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Old Sep 28, 2006, 9:17 AM   #7
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High ISO NR was on, but the long exposure NR was not on. Hopefully tonight I'll be able to try the shots again, with long exposure NR on and off. The lens cap test shot did not show that band. It showed about 20 red white or blue hot pixels though.

This is a crop from the center of the shot during the lens cap test, then resized down 50%. Even here you can see about 10 colored spots. They're scattered randomly across the entire frame.




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Old Sep 28, 2006, 10:07 AM   #8
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Hi, I have a question.*How exactly do you do your lensd cap test and what poist-processing do you do.Do you increase the brightness (in software) to look at the image uniformity or not?If I do not increase the brighness I do not have purple pixels, but if I do I get the image above.
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Old Sep 28, 2006, 11:02 AM   #9
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The hot pixels are probably a result of the long exposure, which is why you haven't seen them in other shots, and is not unusual in long nighttime exposures. THe long exposure NR will probably eliminate most if not all of them. I've looked for the band on a 4th monitor (at work) and still cannot see it:?. I guess my eyes aren't as good as I thought.
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Old Sep 28, 2006, 8:19 PM   #10
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runner77 wrote:
Quote:
Hi, I have a question.�How exactly do you do your lensd cap test and what poist-processing do you do.Do you increase the brightness (in software) to look at the image uniformity or not?If I do not increase the brighness I do not have purple pixels, but if I do I get the image above.
All I did was put the lens cap on, set the shutter speed to 30 sec, ISO to 1600, covered the camera with a towel (it was bright out) and tripped the shutter. No PP on that shot other than cropping and resizing.

I did take the original and cranked up the fill light in Picasa and do get something like your shot runner77. The band that is visible in the star shot shows up clearly as a vertical purple band now. I put the star shot and this adjusted version in layers and played with the visibility and transparency, the purple band in the test shot is in the same place as the star shot.


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