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08/11/2004 09:22:10 PM · #1 |
This is a "100% crop". Not as pronouced as in the RAW and in the converted TIF, I have 5-6 of these small 2-3 pixel spots coming out on my shots, same place--regardless of the lens. Most prevalently on my long exposures. This is very troubling. Any ideas/advice?
I've checked the sensor for dust, none to be seen--though this doesn't look like dust.
Message edited by author 2004-08-11 21:22:56.
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08/11/2004 09:24:18 PM · #2 |
| dead sensor pixels prolly, should be covered by the warrenty. |
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08/11/2004 09:27:25 PM · #3 |
| Looks like dead pixels, I think Canon will replace the sensor for you, but only if you have more than 10 dead pixels... |
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08/11/2004 09:47:45 PM · #4 |
Originally posted by VisiBlanco:
Looks like dead pixels, I think Canon will replace the sensor for you, but only if you have more than 10 dead pixels... |
That's not cool... Minolta did it with just 1 :-/ |
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08/11/2004 11:08:03 PM · #5 |
It's "hot" pixels. There will be more of them show up the longer the exposure takes. It is normal with cameras that do not have a cooled sensor like you would see in a CCD camera used in astrophotography. The big difference in hot pixels and dead pixels is that with dead pixels, it will always be the same pixels. Not always true with hot pixels. In fact, rarely true. See below:
"Hot Pixels
By Mike Pasini, Editor
Imaging Resource Newsletter
You just bought a thousand dollar digicam with full manual control and you want to show off. You take some long exposure night shots and are horrified to see a bright spot in the same part of every picture -- and it isn't a star. It's the infamous hot pixel.
Is your CCD defective?
Actually, no. More than a defect, hot pixels are a fact of life. Understanding them will make you feel better, certainly, and may even suggest when you should return your digicam. So let's take an in-depth look at them.
Your CCD is a grid of elements, each of which is sensitive to brightness.
A hot pixel is created by an element with a higher rate of charge leakage than its neighbors which, on a long exposure, may cross the threshold of an exposed value. Many digicams don't permit exposures longer than a quarter second, which effectively eliminates the chance that any element with a dark current, so to speak, will consistently report an exposure value.
In fact, with a long enough exposure to darkness, a disturbing pattern of exposure will appear from any CCD, because CCD elements tend to leak current. They may not all produce a bright white spot, but they are all -- with a long enough exposure -- capable of reporting exposure in darkness.
In addition to dark current, temperature is also a factor in creating hot pixels. The higher the temperature, the higher the charge leakage. A 10 degree change in temperature can noticeably change what the CCD reports.
Yet another factor is the ISO rating of your CCD. At ISO 400 you'll notice more hot pixels than at ISO 100, simply because the signal is amplified. "
Message edited by author 2004-08-11 23:09:49. |
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08/11/2004 11:52:28 PM · #6 |
Actually you can send your camera to Canon, and they will "map out" the bad pixels (by putting the X,Y coordinates of them into a special table) for free under warranty. The camera firmware then automatically interpolates the "dead pixel" by averaging the pixels around it. This is how most DSLR manufacturers handle "dead" or "hot" pixels, not by replacing the sensor.
Message edited by author 2004-08-11 23:54:49.
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08/11/2004 11:55:37 PM · #7 |
Originally posted by EddyG:
Actually you can send your camera to Canon, and they will "map out" the bad pixels (by putting the X,Y coordinates of them into a special table) for free under warranty. The camera firmware then automatically interpolates the "dead pixel" by averaging the pixels around it. This is how most DSLR manufacturers handle "dead" or "hot" pixels, not by replacing the sensor. |
Ooo sounds hi-tech |
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08/12/2004 01:06:02 PM · #8 |
Sounds like a HACK! :( Poor me. I guess I'll just have to start saving for the 10D replacement. :) teehee
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08/22/2004 02:20:35 PM · #9 |
Maybe I'm confused, but my experience with hot pixels is that they are random. I do quite a bit of long exposure astrophotograpy and have never really seen a distinct pattern with hot pixels. Mapping the pixels should be fairly useless in this case since they will show up differently each time. Now dead pixels would be a different story, but those should be showing up at any exposure, not just long exposures. Ryan's issue is with long exposure so it most likely not dead pixels. One way to check would be to try dark field subtraction and see if that helps. If it is hot pixels, replacing the camera will help as all cameras will have hot pixels with long exposure unless it has a cooled CCD or the ambient temperature is very low.
It may sound funny, but I actually save my long exposure astrophotography for winter when it is cold outside. I do mostly lunar and planetary photography when it is warm to avoid the hot pixel issue. I still get hot pixels in the winter, but not nearly to the degree I do in the summer. |
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