RE: Re: [APML]OT-Drift Alignment

["Franklin A. Holub" <lists@my-spot.com>]

I remember seeing a java based web page that calculated the effect of polar axis misalignment. It's on Michael Covington's website...

http://www.covingtoninnovations.com/astro/Polar.html

Frank



----- Original Message -----
   Serge, I probably should have said "tongue slightly in cheek". I saw some
really clear and expert replies - absolutely depends on a lot of factors
like film format, focal length, direction in the sky your target will be and
exposure length. For what it is worth, Rob Gendler said in one of his S&T
articles that he only aligns using his polar scope and keeps his exposures
to 10 minutes. I don't think anyone will argue with his results.

My observatory mount is very carefully drift aligned for sure. My SP mount
is very difficult to adjust because the center bolt one needs to loosen to
adjust azimuth causes the mount to slump in altitude. Very annoying so I use
the polar scope which my good fortune makes very accurate.

Stuart
----- Original Message -----
From: "Serge Theberge" 
To: "'Discussion of Film Astrophotography'" 
Sent: Tuesday, November 25, 2003 9:30 PM
Subject: RE: [APML]OT-Drift Alignment


> Hi Stuart,
>
> I agree that boredom does put an upper limit to how much time you spend on
> alignment!  However, I would think that there is a fairly big difference
> between "enough alignment" for a 5 minute vs a 45 minute photo exposure
for
> example.
>
> Serge
>
> > -----Original Message-----
> > From: astro-photo-bounces@seds.org
> > [mailto:astro-photo-bounces@seds.org] On Behalf Of Stuart Heggie
> > Sent: Tuesday, November 25, 2003 8:09 PM
> > To: Discussion of Film Astrophotography
> > Subject: Re: [APML]OT-Drift Alignment
> >
> >
> > Serge - knowing you'll get some very expert opinion I'll
> > offer this - drift align till you can't stand the boredom. My
> > attention span is not that long. I polar align my
> > SuperPolaris mount with the polar bore scope and run with it
> > but guide manually. I do end up making some adjustments in
> > Dec but they are not much and I've not noticed any
> > objectionable field rotation on lenses up to 180mm. I only
> > use the SP for piggyback. I drift aligned my G-11 for the observatory.
> >
> > Stuart
> > ----- Original Message -----
> > From: "Serge Theberge" 
> > To: "'Discussion of Film Astrophotography'" 
> > Sent: Tuesday, November 25, 2003 8:01 PM
> > Subject: RE: [APML]OT-Drift Alignment
> >
> >
> > > I have been told that for astrophotography, not only you
> > must have a
> > > good, sturdy mount, but you must have good polar alignment.  I have
> > > seen various rules of thumb about what is "good enough" polar
> > > alignment such as no visible drift @ 200X for 5 minutes,
> > others state
> > > 15 minutes, etc.  My
> > guess
> > > is that there must be some kind of formula (or rule of
> > thumb) linking
> > > "maximum acceptable polar alignment error" to f-speed,
> > magnification,
> > > film grain size, exposure duration, etc.  Can anyone
> > enlighten me on
> > > this?
> > >
> > > Thanks
> > >
> > > Serge Theberge
> > > Toronto Centre
> > > RASC
> > >
> > > > -----Original Message-----
> > > > From: astro-photo-bounces@seds.org
> > > > [mailto:astro-photo-bounces@seds.org] On Behalf Of
> > Franklin A. Holub
> > > > Sent: Monday, November 24, 2003 4:25 PM
> > > > To: Discussion of Film Astrophotography
> > > > Subject: Re: [APML]OT-Drift Alignment
> > > >
> > > >
> > > > I haven't posted in a while but lets see if I can really
> > mess things
> > > > up... I'm going to make a statement that is going to fly
> > in the face
> > > > of years of experience and is going to contradict what we have
> > > > always been told about drift alignment...
> > > >
> > > > But first, a little background...
> > > >
> > > > After a couple of years of being happy with "close enough" polar
> > > > alignment, I installed a perminant pier and I figured it
> > was time to
> > > > "nail" my polar alignment.

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