Re: [APML] LMC with TAK FSQ-106

["westergren" <westergren@netzero.net>]

Hi Monte,

>From your description and photo of your setup, I think you have a classic
case of field rotation due to being off from perfect polar alignment.
Covington's book "Astrophotography For The Amateur" shows a calculated
example, page 280, where the FR for elevation is 7.6 times the FR in azimuth
for the same amount of offset error.  It shows that we need to be right on
in altitude when polar aligning.

If your field rotation shows that the rotation point is off the camera FOV,
you may want to shim the guidescope to get closer to the center.  When you
are guiding, the guide star will not move.  The further away a star is from
the guide star, the more susceptible it is to both field rotation form polar
misalignment and atmospheric differential refraction.  Both of these are
also more of a concern with longer exposures.  The Tak  106 has a wide FOV
and I see the same effects in my Tak in some of my 90 to 120 minute
exposures (I'm using 35mm).

Don
From: "Monte Wilson" <montezinho@bigpond.com>


> HI Don,
>              This is the set up (see link below). I use an STV, it works
> well. The rotation is not centred on the middle of the frame. It seems to
be
> off the image. I know my East West alignment was OK but I think the
> elevation was out and I must admit to being lazy and not checking it
> recently. The closer I get to the pole the worse the problem becomes. I
> expect with such a narrow field of view on the guide scope it would not be
> hard to be guiding off the frame of the shot. In hindsight I should have
> made the guide scope rings more adjustable. I will try however next moth
to
> be sure the two are in looking in the same direction.
>
> http://www.tradepart.com/techinfo/scopeheaters.jpg
>
> Regards
>
> Monte
>
>
>
>
> ----- Original Message -----
> From: "westergren" <westergren@netzero.net>
> To: <astro-photo@seds.org>
> Sent: Monday, August 19, 2002 11:13 AM
> Subject: Re: [APML] LMC with TAK FSQ-106
>
>
> > Monte,
> > How were you guiding your shots of LMC?  You mentioned you got rotation
on
> > your longer shot.  If you were using an Off-Axis-Guider, you may be
> getting
> > ADR, which can be controlled by selecting the right guide star.  If you
> were
> > using a separate guide scope, looking at the center of FOV, the rotation
> is
> > something else.
> > Don
> >
> > From: "Monte Wilson" <montezinho@bigpond.com>
> > Subject: Re: [APML] LMC with TAK FSQ-106
> >
> >
> > > Gee Mike that's real nice of you - thanks. When I got the film back I
> > > thought this shot was the runt of the litter but about 30 mins of PS
> saved
> > > it. You should see the big TIF. It is really something. I took an hour
> > shot
> > > too but my alignment was not as good as I thought and it has rotation.
> > > Having the scope dew up was a blessing disguise.
> > >
> >
> >
> >
> >
> > --  APML Archives at <http://astro.umsystem.edu/apml/>  ---
> >              Unsubscribe at <majordomo@seds.org>
>
>
> --  APML Archives at <http://astro.umsystem.edu/apml/>  ---
>              Unsubscribe at <majordomo@seds.org>
>



--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>