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04-05-2014, 09:18 PM   #1
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Are all of these dead pixels or noise?

See the attached photo! It's a 100% cropped in near center of a long exposure photo taken with K30 and DA21ltd.
Can you see those red, green, ... pixels! Are they dead pixels? so many!? or noise? You see I've put the NR of LR5 to 50! so some level of NR is done to it.

Any thought or advice is appreciated.

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04-05-2014, 09:23 PM   #2
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You might look into "hot" pixels. As I understand it, "hot pixels" are basically just blown out pixels that can show up during long exposures and/or high ISOs? I had a bunch crop up during a trip to the zoo when I took a lot of pictures in very very low light in some nocturnal exhibits. They are not permanently damaged pixels and they "reset" themselves after a short period of time. I am no technical expert (obviously), but you mentioned it was a long exposure, so this could be the same "hot pixel" problem.
04-05-2014, 09:28 PM   #3
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That is an extremely long exposure, 3.5 minutes, hot pixels are inevitable. I'm assuming you didn't use dark frame subtraction in the body, that can help a lot. It takes a second exposure for the same duration with the shutter closed to map the hot pixels.
04-05-2014, 09:32 PM   #4
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QuoteOriginally posted by Steve.Ledger Quote
What was to ISO used?
Check the photo, it's stated there ISO100!

QuoteOriginally posted by severalsnakes Quote
but you mentioned it was a long exposure, so this could be the same "hot pixel" problem.
Well, yes that's 211seconds, I thought hot pixels are same as dead pixels.

---------- Post added 04-06-14 at 12:33 PM ----------

QuoteOriginally posted by Steve.Ledger Quote
Too blurry to tell. Looks like a load of dust.
Colorful dusts!?

I forgot to mention there was a stack of three ND filters (2, 3, 4 stops) in front of lens.

04-05-2014, 09:34 PM - 2 Likes   #5
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QuoteOriginally posted by mtux Quote
I thought hot pixels are same as dead pixels
Nope!

Check out this link: Dead vs Stuck vs Hot Pixels
04-05-2014, 09:42 PM   #6
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QuoteOriginally posted by mtux Quote
I forgot to mention there was a stack of three ND filters (2, 3, 4 stops) in front of lens.
What were you trying to gain by having that long of exposure? A 30 second exposure would be more than enough to give that effect on the water and your image quality would be a lot better.
04-05-2014, 09:46 PM   #7
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QuoteOriginally posted by elliott Quote
What were you trying to gain by having that long of exposure? A 30 second exposure would be more than enough to give that effect on the water and your image quality would be a lot better.
And don't be afraid to crank up the ISO on your K30. I take mine to 1600 with no issues, and 3200 is perfectly usable.

Still not sure the issues you're having are the same ones I had at the zoo...
04-05-2014, 10:06 PM   #8
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QuoteOriginally posted by elliott Quote
What were you trying to gain by having that long of exposure? A 30 second exposure would be more than enough to give that effect on the water and your image quality would be a lot better.
You are right, and this was the first time for me to play with some ND filters, so I wasn't quite sure what I'm gonna get! it was mostly experimental.

QuoteOriginally posted by severalsnakes Quote
And don't be afraid to crank up the ISO on your K30. I take mine to 1600 with no issues, and 3200 is perfectly usable.
I'm not afraid of that at all, and when I need to I go up to 3200, Here as I mentioned above it was mostly experimenting as long as possible shutter speed.

04-05-2014, 10:20 PM   #9
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QuoteOriginally posted by mtux Quote
Check the photo, it's stated there ISO100!
Yeh, sorry - was right in front of my face and I missed it - hence I removed the post, sorry it was too late for you to not see

QuoteQuote:
Colorful dusts!?

I forgot to mention there was a stack of three ND filters (2, 3, 4 stops) in front of lens.
Well yes, why not coloured dust? Should all dust be white???
If you have three ND filters in front of the lens then there's 6 more surfaces for dust to have collected and F11 might be just right to pick it up.

Anyway, I'm probably wrong was just a thought.
04-05-2014, 10:24 PM   #10
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QuoteOriginally posted by Steve.Ledger Quote
If you have three ND filters in front of the lens then there's 6 more surfaces for dust to have collected and F11 might be just right to pick it up.
But dust particles should be bigger than one pixel! aren't they!? and since this is a 100% shot, those dots are only 1 pixel of the sensor!

Thanks guys for ideas and help.
Well I check another photo from that night which is around 120sec long, and these aren't visible there. so it should be the hot pixel which kicks in at this exposure time. and this should be the reason that NR doesn't help!

But how should we get rid of them? is there any way?
04-05-2014, 10:41 PM   #11
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QuoteOriginally posted by mtux Quote
But how should we get rid of them? is there any way?
I know nothing about Lightroom, but Darktable has a tool specifically for hot pixels that does pretty well.
04-05-2014, 11:13 PM   #12
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Lightroom should remove bright / hot pixels automatically.
Your screenshot is blurry and those dots are certainly bigger than 1 pixel in that. How about making your original file available for better answers and suggestions?
04-05-2014, 11:56 PM   #13
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QuoteOriginally posted by severalsnakes Quote
And don't be afraid to crank up the ISO on your K30. I take mine to 1600 with no issues, and 3200 is perfectly usable.

Still not sure the issues you're having are the same ones I had at the zoo...
I don`t think that`s such a good idea for long exposures, as increased ISO creates more heat in the sensor. The same goes for the extended time the shutter is open during long exposures, so those 2 add up.
Noise is usually directly related to heat.
04-06-2014, 12:45 AM - 1 Like   #14
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QuoteOriginally posted by mtux Quote
See the attached photo! It's a 100% cropped in near center of a long exposure photo taken with K30 and DA21ltd.
Can you see those red, green, ... pixels! Are they dead pixels? so many!? or noise? You see I've put the NR of LR5 to 50! so some level of NR is done to it.

Any thought or advice is appreciated.
Enable slow long shutter speed noise reduction and this won't happen. I recommend having it on for exposures longer than 30 seconds.

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04-06-2014, 07:31 AM - 1 Like   #15
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QuoteOriginally posted by TenZ.NL Quote
I don`t think that`s such a good idea for long exposures, as increased ISO creates more heat in the sensor. The same goes for the extended time the shutter is open during long exposures, so those 2 add up.
Noise is usually directly related to heat.
why would increased iso heat up the sensor? as far as i know, changing iso just changes how the camera interprets the signal from the sensor. if anything, with long exposures a higher iso should mean less heat because of the shorter exposure.
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