RE: [APML]: Drive error or bad polar allignment?

["Richmann, Michael" <richmann@cmt.anl.gov>]

The Astro-Photography Mailing List
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The statement as I wrote it is "correct enough for the job at hand".
Yes, if you've used a guidescope and aligned on a star away from the
center of the field of the camera, the center of rotation will not be
coincident with the center of the field of the photograph (I've got an
M31 shot that does this).  However, unless you've used a star a good
distance away, the net effect is still pretty much one where the star
field appears to rotate around a central star, which wasn't the case in
Olle's shot.  Also, as far as Olle's comment is concerned with the field
derotator, I suppose you could view that case as a "worst case"
situation since you've deliberately achieved no polar alignment
whatsoever.  Of course in that situation, field rotation will be extreme
and a derotator is necessary in order to keep the camera aligned with
the star field.

M.

> -----Original Message-----
> From: Genehays2@aol.com [SMTP:Genehays2@aol.com]
> Sent: Friday, July 03, 1998 7:19 PM
> To:   astro-photo@nightsky.com
> Subject:      [APML]: Drive error or bad polar allignment?
> 
> The Astro-Photography Mailing List
> ------------------------------------
> 
> In a message dated 6/30/98 9:03:11 AM Pacific Daylight Time,
> richmann@cmt.anl.gov writes:
> 
> <<   A bad polar
>  alignment should have shown up as a case where the stars appear to
>  rotate around the center of the photo. >>
> 
> Is that statement completely correct?  More technically, isn't it true
> that
> the stars would appear to rotate around the star that was guided upon?
> 
> 
> Gene Hays
> West Covina, CA