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Old Aug 11, 2005, 12:56 PM   #1
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Dear Friends,

Just taken some firework shots and a few 'dusk' shots on my s7000.

Long exposures-1',2',and 3 seconds.

White spots appear in the same place on the frame in the dark blue-black sky.

I seem to remember something about 'hot' pixels during long exposures...or have I got the dreaded cruddy ccd?
:sad:
How best to test how clean the ccd is?

Thanks
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Old Aug 12, 2005, 12:25 PM   #2
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The best way to test is .. do several shots with the lens cap ON. Shutter speed from say 1/10 to 5+sec @ F8. Compare and post the results here. A sample crop of a bad pic will also assist. If it is hot or stuck pixels, there's not much you can do, unless you still have warranty.
JKirk

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Old Aug 12, 2005, 4:21 PM   #3
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......thanks,

I'll try that when I have a mo!

I have taken some more 'normal' daylight shots since and the specks don't seem to be so obvious-but of course these are much 'busier' pictures.

flo
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Old Aug 14, 2005, 8:59 AM   #4
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....a-ha....

an obvious white spot will appear at 1 second-several dozen by5 secs.

but no trace ofthem at faster speeds.

Presume that theseare hot pixels-the effect appears to 'bleed' into adjacent ones making the spots more noticeable.

I guess we have to live with it? Isn't this an unfortunate failing of ccd technology?

Wouldn't crud on the ccd appear as BLACK marks?

Thanks for yr help.
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Old Aug 14, 2005, 2:25 PM   #5
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Try in RAW mode, as jpeg compression will emphasise any hot pixels.

Its normal(ish) to have a few hot/warm pixels that are 'on' with exposures greater than a few seconds, and there's not a great lot you can do about it with current CCD technology.

My S7000 has about 2 hot pixels on 1 second exposures (with the lens cap on), and about 5 on 10 second exposures - and from what others have said thats about average.


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Old Aug 23, 2005, 6:17 PM   #6
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there are programs that can remove hotpixels, very usefull
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Old Aug 24, 2005, 4:30 AM   #7
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floricicia wrote:
Quote:
I guess we have to live with it?

Not quite, if you're willing to invest a few moments of work.

After shooting the night shot, take the same shot (same aperture, shutter speed) with the lens cap ON. This second shot will yield a black pic with only the hot pixels. Subtractthe second image from the first image in Photoshop -> the result should be a substantial alleviation of the hot pixels in the first image.

Frankly spoken, I've never tried it myself. But supposedly it works wonders!



cheers,

nymano.
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Old Aug 24, 2005, 8:13 AM   #8
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..thanks for those thoughts.....

I have d/loaded a nifty little program for removing hot pixels and it has cleaned up my firework pics a treat!

flo
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Old Aug 24, 2005, 12:18 PM   #9
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floricicia wrote:
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..thanks for those thoughts.....

I have d/loaded a nifty little program for removing hot pixels and it has cleaned up my firework pics a treat!

flo

and which program may that be?
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Old Aug 24, 2005, 1:21 PM   #10
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.....'HotPixels CCD noise eliminator'

http://www.mediachance.com

They also provide a 'black-frame' solution similar to the idea you were talking about.

flo
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