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Old 22-03-2010, 05:33 AM
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JD2439975 (Justin)
Cloud hater

JD2439975 is offline
 
Join Date: Feb 2009
Location: Conondale QLD
Posts: 493
40D ISO-Exposure Noise Mosaic

I hear people say "go long on the sub exposures"...well that may be OK for those with CCD's cooled to 30 below ambient but what about us suckers with uncooled DSLR's unfortunate enough to live in the tropics?
I laugh when I hear a CCD owner worried because they can't get it under -20 C, hell I'm happy if gets below +20 C

I 'd noticed my ISO800 @ 5 min shots always seem rather noisy while the ISO800 2min & ISO1600 30sec shots seemed so much smoother, so I decided to do an ISO-exposure of my camera.
Starting with the lowest to highest ISO through the lowest to highest exposures, the lens was removed & replaced with the body cap, the viewfinder was also covered.
The whole exercise took about 7 hours with the average temp at 26 deg, dropping slightly in favour of the longer exposures, temps can be found in the second image.
The first image is a mosaic of all (RAW) darks taken, resized & saved as 16bit TIF, mosaic'd before tweaking the levels for ease of display.
The images were also feed into an online "average colour of the image" applet where I noted the black levels, ISO100 was 99% so I took the remainder 1% as noise level.
Plotting these and extrapolating for the full ISO range of the 40D I came up with a table of noise levels, note the added "missing ISO's" 2000 & 2500 that put ISO3200 in perspective.
Now this is rough & no doubt needs tweaking.

Remembering this is taken at 26 deg C does this look about right??
I was thinking...
ExtremelyLowNoise - masterpiece on bright objects...yeah right.
VeryLowNoise - ditto.
LowNoise - Lovely for that special image.
MediumNoise - a happy medium.
HighNoise - where you go for a quick snap.
VeryHighNoise - drunk or desperate or both.
ExtremelyHighNoise - noobies on a rampage.

Either I lengthen my exposure & lower my noise by lowering my ISO or I pick through Berts old posts on how he made his fridge.
Any thoughts?

Justin.
Attached Thumbnails
Click for full-size image (40D ISO-ExposureDarkMap.jpg)
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Click for full-size image (40D Dark Temps.jpg)
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Click for full-size image (40D ISO-Exposure Noise Mapping.jpg)
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