Re: Why .avi format ?

On 28 Nov 2005 04:40:37 -0800, "atasselli@xxxxxxxxxxx"
<atasselli@xxxxxxxxxxx> wrote:

>> This is functionally equivalent to high order adaptive
>> optics.
>
>Not really. High order adaptive optics allow to correct the exit pupil
>phase differences while select-and-stack simply rejects those that do
>not qualify.

Which, in terms of the final image, is substantially similar. Sure,
discarding bad images is equivalent to AO with very poor QE, but all the
same, I consider such processing to effectively be post-processed AO.


>>Readout noise makes for a stiff noise penalty...
>
>This depends on the read-out noise. The lower it is the less different
>the 2 techniques are.

Of course, but realistically all cameras now being used are high readout
noise. Webcams are particularly poor in this respect.


>> Once you start imaging DSOs, you need long exposures- many minutes is
>> usually required to maximize S/N.
>
>Not really. I've been imaging DSOs for the past 4 years without ever
>taking exposures longer than 120s, 45s to 60s being the most common
>durations. With low read-out noise camera there are benefits in using
>short exposures.

Unless you are imaging under horribly light polluted skies, it is likely
that you are not optimizing your S/N with such short exposures. That
isn't the same as saying that you aren't getting good results, however-
just that they could be better.

There can be benefits to short exposures, particularly if your equipment
isn't good enough to support accurate tracking for long periods. I have
an experimental camera with essentially zero readout noise. You can do
some very cool things with it, such as building the final image
dynamically from subsecond exposures. The actual image is used for
guiding, and the current sum image is always available, so the exposure
can be run until the desired goal is visible. Focus can be monitored and
controlled throughout the exposure, and bad frames can be rejected on
the fly. Cool stuff, but these sensors don't seem to be under very
aggressive development (although I guess they are being developed for
military applications, since they perform better than the best
intensifier-based night vision equipment).

_________________________________________________

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

Relevant Pages

  • Re: D700 sample photos up to 25,600 ISO
    ... With multiple exposures it is possible to get ... significantly lower ISO. ... the noise is greatly reduced while the ...
    (rec.photo.digital.slr-systems)
  • 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: Time for a change...
    ... I always have to stack exposures of 1-2 minutes or less ... scopes too. ... LX200 OTA I already have? ... noise is far less of a concern than the sky noise. ...
    (uk.sci.astronomy)
  • 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)
Loading