Re: dynamic range and thermal noise

Roger N. Clark (change username to rnclark) wrote:
<snip>
Yes, the square root of the dark current is the thermal noise.
Dark current is generally low in modern cameras, a fraction
of an electron per second, so it takes a while for it
to become a factor. It is higher with higher temperatures,
like 100F it could be several/second. The simple solution
is take multiple short exposures and add them together.
Effectively, with this technique, dark current is not an issue.

Roger

The first part is correct. The second isn't. Combining several exposures reduces the noise according to the square root of the number of images. Combining four photos
lowers the noise only by a factor of 2. To reduce noise by a factor of 4, you would have to combine 16 images.
.

Relevant Pages

  • Re: too much light
    ... one area where film cameras may have an advantage. ... 'noise' that digital sensors produce with very long exposures (more ... Noise from long exposures (thermal dark current noise) ...
    (rec.photo.digital)
  • Re: dynamic range and thermal noise
    ... by the noise which is produced in the various stages. ... in calculating dynamic range? ... I believe you are really talking about dark current, ... exposures dark current can become an issue. ...
    (rec.photo.digital)
  • Re: Why .avi format ?
    ... >exposure images over fewer long exposure images? ... There are many discussions about noise issues, just not a lot on this ... It is primarily readout noise that determines your S/N. ... Because of the short exposures, ...
    (sci.astro.amateur)
  • Re: dynamic range and thermal noise
    ... by the noise which is produced in the various stages. ... in calculating dynamic range? ... I believe you are really talking about dark current, ... exposures dark current can become an issue. ...
    (rec.photo.digital)
  • Re: Long exposure vs. multiple exposure
    ... There are different sources of noise in digital images. ... Readout noise occurs with every image however, and for short exposures is a ... With a digital camera, your options are much more limited. ...
    (sci.astro.amateur)