does that fix thermal noise? I was reading loong exposures with digital cameras result in thermal noise
does that fix thermal noise? I was reading loong exposures with digital cameras result in thermal noise
Last edited by Sleev; Thu Nov 18th, 2010 at 03:12 PM.
I have no idea what you're talking about.
Thermal noise? Do you mean luminance noise?Originally Posted by Sleev
Luminance noise is more related to ISO than exposure length - although they work together. Also, noise isn't specific to digital cameras; high ISO films suffer the same problem, although then it was referred to as "grain".
But yes - high ISOs can result in noticeable, and sometimes problematic, noise. This is a function of how the camera amplifies light on the sensor at high ISOs, which is dependent upon its firmware (which are propriety and closely guarded secrets of each manufacturer). A lot of the newer cameras can handle very high ISOs without a lot of noise (see Canon 5D MarkII, Nikon D7000, etc.).
High ISOs result in short shutter speeds, even with night photography. So if you crank a Canon 5DmkII up to an expanded ISO of 25,600, you will likely have a very short shutter speed, resulting in a lot of noise. While modern software can almost eliminate noise (see Lightroom v.3), there are tricks to avoid it. By setting a lower ISO and a longer shutter speed, the sensor is exposed for a longer duration to the available light (instead of having to amplify it). This results in reduced noise.
So lower ISOs with longer exposure times actually improve noise performance. The downside to this is, you will deal with star movement. So if you are trying to capture stars in a fixed position - which typically requires an exposure of LESS than 30 seconds - you will need a pretty high ISO, and a damn good camera (see the Nikon and Canon models noted above).
This is great. Is that true out of camera DOF, or postprocessing?
Ya out of camera DOF.
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