Colour noise during long exposure?


Mar 1, 2012
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#1
Hi Bros and Sis,

I took a long exposure shot with my NEX-6 and the rokinon 8mm Fisheye lens, and I noticed some strange colour pixels in the shadow areas. I uploaded the full-res pic, please take a look at the forest areas in my picture (at 100%). The pixels were not very noticeable (but is there) in the raw files. I did some PP to bring back some shadow details and the colour pixels become very apparent. Anyone knows why? Is it because of my lens? sensor? long-exposure NR, or the lack of it (I did not turn on LE NR)? Or are there really spirits living in the forests?

Taken at f/8 ISO 200 exposure 25s

 

Rashkae

Senior Member
Nov 28, 2005
19,105
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#2
Hi Bros and Sis,

I took a long exposure shot with my NEX-6 and the rokinon 8mm Fisheye lens, and I noticed some strange colour pixels in the shadow areas. I uploaded the full-res pic, please take a look at the forest areas in my picture (at 100%). The pixels were not very noticeable (but is there) in the raw files. I did some PP to bring back some shadow details and the colour pixels become very apparent. Anyone knows why? Is it because of my lens? sensor? long-exposure NR, or the lack of it (I did not turn on LE NR)? Or are there really spirits living in the forests?

Taken at f/8 ISO 200 exposure 25s
bizarre. Did you try with DRO off?
 

digitalpimp

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Oct 25, 2008
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#3
I can't see them (I'm on mobile), but the way you describe them leads me to believe they are hot pixels. It happens when you do long exposures with the LENR off. Although I kinda find it odd they manifest in just 25 secs. Try shooting again with the LENR on and see if the hot pixels still show.
 

Mar 1, 2012
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0
Singapore
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#4
I can't see them (I'm on mobile), but the way you describe them leads me to believe they are hot pixels. It happens when you do long exposures with the LENR off. Although I kinda find it odd they manifest in just 25 secs. Try shooting again with the LENR on and see if the hot pixels still show.
I shall try again with LENR on. Hmm, not very familiar with hot pixels, but if they manifest in just 25 s, does it mean it's a bad thing?

bizarre. Did you try with DRO off?
DRO was on auto. It affects raw files?
 

digitalpimp

Senior Member
Oct 25, 2008
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#5
I shall try again with LENR on. Hmm, not very familiar with hot pixels, but if they manifest in just 25 s, does it mean it's a bad thing?
I'm assuming it is (note: I'm no expert). Your ISO may have also contributed. Personally, I wouldn't do long exposures at ISO200, with or without hot pixels. Anyway, keep your lens cap attached when you do your test so you'll see exactly where and how many your dead pixels are.

Just to share with you my longest single exposure using an A700. That's 30 minutes without LENR. Never got to try with LENR turned on though.


My A77 can go 12 minutes+ without glitch, and my A300 can do 4.
 

donut88

Senior Member
Nov 14, 2008
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#6
Hi Bros and Sis,

I took a long exposure shot with my NEX-6 and the rokinon 8mm Fisheye lens, and I noticed some strange colour pixels in the shadow areas. I uploaded the full-res pic, please take a look at the forest areas in my picture (at 100%). The pixels were not very noticeable (but is there) in the raw files. I did some PP to bring back some shadow details and the colour pixels become very apparent. Anyone knows why? Is it because of my lens? sensor? long-exposure NR, or the lack of it (I did not turn on LE NR)? Or are there really spirits living in the forests?

Taken at f/8 ISO 200 exposure 25s
Try doing at f/10 or 12 at lowest ISO
 

Rashkae

Senior Member
Nov 28, 2005
19,105
12
0
#7
That's an unusually high amount of hot pixels.
 

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