Thanks a lot Vinz for the information. In fact, using astrosnap and King , I am
within 1 arcminute in AZ and EL . Seems to be good to go on...

André











--- In astrosnap@yahoogroups.com, "Vincent STEINMETZ" <xmcvs@...> wrote:
>
> Hello,
>
> so yes it is important !
>
> if you use a guidescope you are a canditate for field rotation :
>
> the problem :
>
> increases when you go toward polaris, for example M82 is a pain if you want
> to autoguide without a nice polar alignement
>
> increases when your guidescope aimes far away from the image field.
>
> I would strongly encourage you to be within
>
> 20 arcmin from the pole, for imaging around DEC 0
>
> 10 arcmin for DEC45
>
> 5 min for DEC60
>
> and aim you guidescope near the image field ...
>
> astroart is a really good program to do the job, use the shortest focal you
> can , for ex with a reducer for webcams.
>
> There are some calculation here :
>
>
http://pagesperso-orange.fr/mesxxi.durand/tolerances.htmlhttp://pagesperso-orang\
e.fr/mesxxi.durand/tolerances.html
>
>
> Vinz
>