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(meteorobs) RE: meteorobs-digest V1 #178

George Zay wrote:

>I use guided exposures for a variety of reasons. Mostly for personal
>preference. I prefer to see the sky looking like a sky rather than a lot of
>star trails.  Also, when I get a meteor in the field, it's easier for me to
>figure it's path...ie begin and end points. Analysis of unguided images is
>done routinely by some, but I believe the longer the exposure, the more
>uncertain these points become and yes I would think more difficult.  unless
>you know almost exactly where the camera was pointing, you may not be able 
to
>know what 6 stars to get a good fix on.  As a routine, I always list
>approximately where my camera is pointing for each exposure...even then the
>print sometimes looks foreign. The sky looks different due to the addition of
>many stars you normally don't see

I would like to add some comments to these statements. It is hard to say 
whether guided or unguided exposurs are better. In my opinion the following 
advantages for each hold:

Unguided exposures:
  -	easier and cheaper setup
  -	accurate measurements because of absence of guiding errors. It 
does not matter how long the exposure is, because you can simply correct for 
the time difference between the start of the exposure and the time of 
appearance of the meteor.
  - 	better suited for double-station photography, because the camera 
does not move away from the aiming point

Guided exposures:
  -	time of appearance of meteor and start and end time of exposure are 
not required to obtain true right ascension and declination of the meteor 
positions. For double-station photography the time is needed in order to 
calculate azimuth and zenith distance from the equatorial coordinates.
  - 	when perfectly guided, even more accurate measurements, because 
you do not need to "guess" what is the true beginning point of the star trail.

Kind regards,

Marc de Lignie

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Marc de Lignie
Prins Hendrikplein 42                        Tel. +31 (70) 320 5673
NL-2264 SN  Leidschendam            Fax. +31 (70) 332 6477
The Netherlands                                E-mail: mcdelign@pidot net

Predicted progress always fails. Real progress is all the small
steps you realize to have made when looking back in time.
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