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Re: [APML] Coma Corrector for 10" f/4.72 Newton

To: astro-photo@seds.org
Subject: Re: [APML] Coma Corrector for 10" f/4.72 Newton
From: Walter Koprolin <a9125657@unet.univie.ac.at>
Date: Fri, 7 Mar 2003 17:17:26 +0100 (MEZ)
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Hi Brian,

Thank you for the info and the data, this looks like the way I will do it.
However, I am a little bit concerned about the vignetting which the
Lumicon OAG and the Lumicon coma corrector will introduce. While maybe not
severe and correctable in Photoshop, I usually go for near-perfect orignal
(unprocessed) slides to be shown in slide shows.

  Walter Koprolin
  Gallery of Astrophotography & CCD, Observation Reports,
  Telescope Testing: http://www.astro.univie.ac.at/~koprolin


On Fri, 7 Mar 2003, Brian Lula wrote:

> Hi Walter,
>
> I would second Bobby's comments and strongly advise you to stay away from using a
> guidescope for guiding. You just can't make the structure and optical supports stiff
> enough to overcome differential flexure between the main OTA and the guidescope
> especially with a Newtonian. BTW the Lumicon coma corrector has a clear aperture of
> 47mm and the OAG closer to 45.
>
> Best regards, Brian Lula
>
>
>  The On 7 Mar 03, at 13:13, Walter Koprolin wrote:
>
> > Hi Bobby,
> >
> > Thank you for your advice. Considering your experience, I am drawn towards
> > off-axis guiding, even if that means redesigning the Newton for more
> > backfocus etc. Do you know is the free aperture of the Lumicon OAG and
> > coma corrector, is it 2.7"? Do you have and idea where to obtain such a
> > device now, since Lumicon does no longer exist?
> >
> > Yours sincerely,
> >
> >    Walter Koprolin
> >    Astrophoto-Gallery, Observation Reports, Telescope Testing:
> >    http://www.astro.univie.ac.at/~koprolin/
> >
> >
> > On Thu, 6 Mar 2003, Bobby Middleton wrote:
> >
> > >
> > > ----- Original Message -----
> > > From: "Walter Koprolin" <a9125657@unet.univie.ac.at>
> > >
> > >
> > > > Hi Bobby,
> > > >
> > > > Thank you for the reply. So, both the Vixen and the Lumicon coma
> > > > correctors seem to be interesting options. Does anyone have the
> > > > measurements of these correctors (diameter/length)? I need them to specify
> > > > the focusser I will need.
> > >
> > > I'll get you the dimensions this pm Walter.
> > > >
> > > > I want to guide the Newton, which will be custom-made and (hopefully)
> > > > very rigid, with a guide scope mounted side-by-side. I hope to minimize
> > > > vignetting by not using a T-mount, but a custom-made adapter for my Nikon
> > > > F3, and a secondary mirror of suitable size.
> > >
> > > I attempted this with my 8" f/4.25. Many (most) shots had flexure. I
> > > considered everything to be built very sturdy but I soon went to an OAG. I
> > > am also using a guidescope with a heavily built Takahashi BRC 250 and well
> > > built guidescope. I get some flexure on at least half my exposures. If
> > > possible I *highly recommend* an OAG. This will not be easy with the Vixen
> > > because you will have to use guidestars from before the corrector. At f/4.25
> > > these comatic guidestars were simply 2 seagull wings unless at exact focus.
> > > and the st-4 had to be at exact focus also. And I still had some vignetting.
> > > I'd recommend the Lumicon OAG and coma corrector. The OAG is designed to
> > > accept the corrector withy threads for it to screw into.
> > > Bobby
> > >
> > > >
> > > > Thanks again,
> > > >
> > > >    Walter Koprolin
> > > >    Astrophoto-Gallery, Observation Reports, Telescope Testing:
> > > >    http://www.astro.univie.ac.at/~koprolin/
> > > >
> > > >
> > > > > Hi Walter.
> > > > >
> > > > > I used the Vixen coma corrector for my f/4.25 homebuilt 8" newt. I can't
> > > > > remember its clear apreture but it was the largest corrector availiable.
> > > It
> > > > > would require the direct-wide adaptor and also a special OAG that would
> > > hold
> > > > > it plus a custom machined adaptor to fit it to the OAG . I was able to
> > > use a
> > > > > 2.7" Lumicon OAG that was once availiable but you probably won't be able
> > > to
> > > > > find one of these now.
> > > > > The Vixen corretor was designed for an f/4 system. For my f/4.25 it had
> > > good
> > > > > correction. Would correction be satisfactory at f/4.7? I don't know.
> > > > > The alternative is the Lumicon corrector which is designed for a f/4.5
> > > > > system. You should be able to find a used one. It fits into Lumicon's
> > > Newt
> > > > > ez guider and you probably could find one of these too. You will have
> > > some
> > > > > vignetting. It won't be objectionable except right at the corners but
> > > this
> > > > > might be the most practical solution.
> > > > > Vignetting and uneven illumination of fast mirrored systems is one of
> > > their
> > > > > design realities (along with the need for correction). The only way
> > > around
> > > > > this vignetting is to use expensive custom accessories and after all
> > > that
> > > > > the T mount of your 35mm camera will cause vignetting also.
> > > > > Bobby Middleton
> > > > >
> > > > >
> > > > > I read, and takes a special direct-wide photo adaptor,
> > > > > > but will it work for my f/4.72 system? It is built for the R200SS,
> > > which
> > > > > > is f/4. I also came across a Lumicon model, but found no additional
> > > data
> > > > > > on that one.
> > > > > >
> > > > > > I am looking for pin-point stars and no vignetting out to the edges of
> > > > > > 35mm format. Any ideas?
> > > > > >
> > > > > > Thanks in advance for your help,
> > > > > >
> > > > > >   Walter Koprolin
> > > > > >   Astrophoto-Gallery, Observation Reports, Telescope Testing:
> > > > > >   http://www.astro.univie.ac.at/~koprolin/
> > > > > >
> > > > > > _______________________________________________
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> > > > >
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> > > > >
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>
>
>
> Brian Lula
> Polytec PI, Inc.
> (508) 832-3456
>

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