Re: [APML] Optimum focal length for guidescope?

[Steve <sc02492@yahoo.com>]

Does anyone know why the e-finder/STV combination can
work well as a guidescope, even though the focal
length is only in the 100 mm range?  This is so short,
that I'm surprised that it works as well as it does
for moderate focal length scopes.  Is there something
about the STV itself that compensates for the short
focal length of the e-finder?

Steve Cannistra

--- Michael Stecker <mstecker@dslextreme.com> wrote:
> Hello Stuart:
> 
> When I was manually guiding back in "those bad old
> days", I found that if I
> used a guiding eyepiece (equivalent) of
> approximately 6 mm at a focal length
> equal to that of the photographing telescope, then I
> would get good guiding.
> Richard Schwartz once told me that you could get
> good guiding with the ST-4
> with a guide scope of 1/2 the focal length of the
> one used for the photo.  I
> routinely guided my 1085 mm focal length telescope
> with an ST-4 on a guide
> scope of 900 mm.
> 
> 
> Michael Stecker
> mstecker@dslextreme.com
> 
> My Web Site:
> http://www.homestead.com/mstecker/index.html (INDEX)
> http://www.homestead.com/mstecker/astrogallery.html
> (Astroimage Index)
> http://www.homestead.com/mstecker/placesindex.html
> (Places Index)
> 
> 
> 
> ----- Original Message ----- 
> From: "Stuart Heggie" <stuart.j.heggie@sympatico.ca>
> To: "Discussion of Film Astrophotography"
> <astro-photo@seds.org>
> Sent: Sunday, July 27, 2003 11:41 AM
> Subject: Re: [APML] Optimum focal length for
> guidescope?
> 
> 
> > Chris, that is very helpful. With my ST-7 then I
> can go anywhere over
> > 800mm for guiding the anticipated purchase. When
> guiding manually, I'll
> > use my apo barlow and be able to guide at double
> that. Looks like I'm
> > fine using the 1000mm achromat to guide the 800mm
> scope. Manually and
> > with a barlow, that scope would give me 167x but
> the most I'd be guiding
> > manually would be a 180mm lens.
> >
> > Stuart
> >
> > Chris Cook wrote:
> >
> > >Stuart -
> > >
> > >If you're using a ST-4 you can easily get away
> with less than a 1:1
> guiding
> > >ratio.  Currently I'm guiding my FS102 (which is
> 600mm @ f/6)with a 660mm
> > >guidscope (60mm f/11 refractor).  If you are
> manually guiding, I would
> stick
> > >with guiding with at least 200x.  Back before
> autoguiders, guys like Kim
> > >Zussman in CA would guide at ~600x if I'm not
> mistaken.  Granted he was
> > >shooting prime focus through a C11 @ f/10.
> > >
> > >Chris
> > >
> > >----------------------------------
> > >Chris Cook
> > >Astronomical & Nightscape Photography
> > >www.abmedia.com/astro
> > >
> > >-----Original Message-----
> > >From: Stuart Heggie
> <stuart.j.heggie@sympatico.ca>
> > >To: Discussion of Film Astrophotography
> <astro-photo@seds.org>
> > >Date: Sunday, July 27, 2003 1:02 PM
> > >Subject: [APML] Optimum focal length for
> guidescope?
> > >
> > >
> > >
> > >
> > >>Okay - since it is quiet (and raining) I'll pose
> a question.
> > >>
> > >>As I look over my setup - I'm guiding a 400mm
> apo lens with a 1200mm
> > >>guidescope. Seems odd to have 3x the focal
> length on the guidescope but
> > >>seems to work. I may downsize the guidescope to
> fund the purchase of a
> > >>new telescope. If the 400mm apo lens stays in
> the stable and I buy an
> > >>800mm fl imaging scope - what would be an ideal
> focal length for a
> > >>guidescope for both (i.e. for the 800mm Vixen
> R200SS - 8" f/4
> > >>Newtonian)? I have a Vixen/Celestron 1000mm
> 102mm f/9.8 achromat now
> > >>which I'm very pleased with and could continue
> to use.
> > >>
> > >>Stuart
> > >>
> > >>_______________________________________________
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> > >>
> > >>
> > >>
> > >
> > >_______________________________________________
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> > >
> > >
> > >
> >
> >
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> >
> 
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