07-18-2010, 02:07 PM
You can actually switch this feature on and off with Canon, long exposure noise reduction, that is. However, this is not what affects astrophotography. It reduces heated sensor noise, by substracting the pattern noise from a sensor that is hot because of a long exposure. It is the only way to do this, and is different literally from camera to camera, as no individual sensor is the same in this regard. Furthermore, funnily enough, this is a technique borrowed from astrophotography in the first place <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
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But that is not what I am referring to, long exposure NR is with a black frame. And Nikon has the feature too (which you can switch on and off). The type of NR you can see Nikon apply is NOT that kind of NR, and it switches on at 3secs for some models to 0.5 sec or so on other models. You can find it by careful RAW data analysis.
Whether this is connected to the bump you see in dynamic range in DXOmark data for the D3s at ISO 25600 I do not know. The graphs of DXOmark do not show the used exposure times.
Anyway: My point is that you can see (extra?) NR kick in with Nikon models when they pass a certain exposure time, and this is NOT connected with "long exposure" black frame subtraction NR.
[quote name='wim' date='18 July 2010 - 02:44 PM' timestamp='1279460649' post='1093']
With regard to the 5D II: it doesn't affect it. It was creating noise where there isn't any. It is in a way a similar issue to the black pixel syndrome, where in high iso shots with high contrast transitions, the neighbouring pixels got clipped by the A/D converter hardware to 0 values due to the preceived too big difference in eV values. It is a strange phenomenon in that neigbouring signal outputs are somehow interrelated, which is a physics thing as far as I understand (i am no expert on this, BTW, so this is my layman interpretation). The boundaries between two neighbouring well sites is not as clear cut, it seems, as we would expect.
However, Raw is still Raw with the 5D II, as all pixe values are still there. IOW, th eproblem lies in gettign out the real values, not so much trying to get rid of noise, with these issues anyway.
Kind regards, Wim
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But that is not what I am referring to, long exposure NR is with a black frame. And Nikon has the feature too (which you can switch on and off). The type of NR you can see Nikon apply is NOT that kind of NR, and it switches on at 3secs for some models to 0.5 sec or so on other models. You can find it by careful RAW data analysis.
Whether this is connected to the bump you see in dynamic range in DXOmark data for the D3s at ISO 25600 I do not know. The graphs of DXOmark do not show the used exposure times.
Anyway: My point is that you can see (extra?) NR kick in with Nikon models when they pass a certain exposure time, and this is NOT connected with "long exposure" black frame subtraction NR.
[quote name='wim' date='18 July 2010 - 02:44 PM' timestamp='1279460649' post='1093']
With regard to the 5D II: it doesn't affect it. It was creating noise where there isn't any. It is in a way a similar issue to the black pixel syndrome, where in high iso shots with high contrast transitions, the neighbouring pixels got clipped by the A/D converter hardware to 0 values due to the preceived too big difference in eV values. It is a strange phenomenon in that neigbouring signal outputs are somehow interrelated, which is a physics thing as far as I understand (i am no expert on this, BTW, so this is my layman interpretation). The boundaries between two neighbouring well sites is not as clear cut, it seems, as we would expect.
However, Raw is still Raw with the 5D II, as all pixe values are still there. IOW, th eproblem lies in gettign out the real values, not so much trying to get rid of noise, with these issues anyway.
Kind regards, Wim
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