Re: Why .avi format ?

On Sun, 27 Nov 2005 20:58:48 -0500, Tom Rauschenbach
<tomsusenet@xxxxxxxxxxxxxx> wrote:

>That makes a great deal of sense to me. Especially in light of statements
>that seem to imply that long exposures aren't really needed for CCD data
>collection. Although I have to wonder why there aren't discussions
>about readout noise/image. What are the costs and benefits of many short
>exposure images over fewer long exposure images ? Of course tracking
>issues are an obvious one.

There are many discussions about noise issues, just not a lot on this
forum. Readout noise is the primary noise source when you are doing any
kind of video astronomy, either with a webcam or a video camera and
frame grabber. It is primarily readout noise that determines your S/N.
Because of the short exposures, dark current noise is insignificant.

There is only one fundamental benefit of short exposures- the ability to
capture images during brief moments of atmospheric stability. A
collection of many images can be graded for quality and the bad ones
discarded. This is functionally equivalent to high order adaptive
optics. Readout noise makes for a stiff noise penalty, but with hundreds
or thousands of images the noise is substantially reduced. But the
technique is only useful for very bright objects- the Sun, Moon, and a
few planets.

Once you start imaging DSOs, you need long exposures- many minutes is
usually required to maximize S/N.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
.

Relevant Pages

  • Re: Why .avi format ?
    ... >>>Readout noise makes for a stiff noise penalty... ... With low read-out noise camera there are benefits in using ... > that you are not optimizing your S/N with such short exposures. ... > an experimental camera with essentially zero readout noise. ...
    (sci.astro.amateur)
  • 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)
  • Re: D700 sample photos up to 25,600 ISO
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    ... In many papers it is suggested to recover first the non linear ... different exposures. ... mixing of the images is carried out in that domain. ... maximizes signal to noise ratio under the assumption of an additive ...
    (sci.image.processing)
  • Re: dynamic range and thermal noise
    ... Effectively, with this technique, dark current is not an issue. ... Combining several exposures reduces the noise according to the square root of the number of images. ...
    (rec.photo.digital)