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hot pixels.

FORUMS Photography Talk by Genre Astronomy & Celestial Talk
Thread started 15 Apr 2012 (Sunday) 17:13   
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popsandme
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ive recently attempted a startrails pic and when ive come to process all the images in lightroom and then startrails.exe ive noticed that i have suffered from hot pixels, i had 120 frames all shot at 30" expesure at f5.6 iso 200 on a cold night so i thought i had no worrys about my sensor over heating.....now im assuming they were hot pixels, they were tiny white dots all appearing in the same place in every shot and are only noticable in the night sky/startrail pictures.....now my question is....does this mean the end of my sensor?? or could it just need a good clean??
i would post a picture up for you all to see but i was that annoyed i deleted them all in disgussed as i had spent nearly 2 hours on acold windy cliff top freezing my nads off for no end result except for a potentially dodgy sensor......
now ive just taken a shot indoors with the setting of 1/2000, f32 & iso 100 and uploaded it to my pc and there are no white spots, could this mean that my sensor wasnt warmed up enough for the startrails pictures??
thanks in advance for your advice

Post #1, Apr 15, 2012 17:13:07


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SteveInNZ
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No. It's not really anything to be concerned about. The term "hot pixel" is somewhat over dramatic. Most hot pixels are simply ones that are a bit more sensitive to their own heat than the ones around them. You wouldn't notice them in the majority of shots and they only start to show up on longer exposures. Even then, you wouldn't have noticed if you weren't adding them all together in the startrails program.
It's a shame that you deleted them. You could have shot some dark frames after the fact (not as good but much better than none) and the startrails program would probably have eliminated them.
Next time, shoot half a dozen frames with the same settings but with the lens cap on when you start and another half a dozen at the end. These are the dark frames.
Hope that helps and your nads have thawed out.

Post #2, Apr 15, 2012 19:57:27


"Treat every photon with respect" - David Malin.

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popsandme
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many thanks for reassuring my steve, i feel a little better now, cheers mate....is there anything that i can do to help reduce the ammount of them the next time i try to attempt the startrail shot again? i did one 6 months ago but there was a little light pollution so the sky was more orange and the white spots weren't a noticable

Post #3, Apr 16, 2012 05:55:08


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SteveInNZ
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Yep. This is the solution -

Next time, shoot half a dozen frames with the same settings but with the lens cap on when you start and another half a dozen at the end. These are the dark frames.

The startrails program allows you to provide these dark frames and it will subtract them off each of the star pictures.
This is what the camera does when you turn on long exposure noise reduction. It takes another frame with the shutter closed and subtracts it from the picture. If you used that function your star trails would have big gaps in them. Doing them yourself and subtracting the dark in startrails means that the gaps are negligible.

Post #4, Apr 16, 2012 15:04:19


"Treat every photon with respect" - David Malin.

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popsandme
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top man steve, i understand it now, you have been a great help cheers

Post #5, Apr 16, 2012 17:05:08


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hollis_f
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One thing you can try is the oft-reported remapping method. This will, supposedly, re-map the hot pixels so that they aren't used. Here's the process...


  1. Remove the lens
  2. Put on the body cap
  3. From the menu select 'Manual Cleaning' and start it up
  4. Wait around 1 minute
  5. Switch off power to the camera
  6. Enjoy images free of hot pixels.

Now I have to say that I've tried this a couple of times on different cameras with no joy. But several people claim that it works. And it can't do any harm.

Post #6, Apr 17, 2012 04:44:23


Frank Hollis - Retired mass spectroscopist
Give a man a fish and he'll eat for a day. Teach a man to fish and he'll complain about the withdrawal of his free fish entitlement.
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popsandme
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thanks hollis.......ive been planning to do just that the next time my battery is fully charged, got a lot on at the moment

Post #7, Apr 17, 2012 09:34:40


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hot pixels.
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