Re: [APML] guidescope / setup question

["bert katzung" <katzung1@home.com>]

Hi Aike:
I can't answer all of your questions, but I have tried guiding with an ETX
and a refractor and I can tell you that you were given very bad advice
there! Yes, flexure is always a problem, but so is mirror shift. The ETX
focal length is just as long as the refractor you're considering so it has
no advantage/disadvantage there. The ETX definitely has mirror shift, which
a refractor guidescope does not have. The focus shift with an ETX is much
worse than with either refractor that I use. Yes the refractor OTA is much
longer than the ETX but with good mounting, that should not be a problem. I
use the A-P 80 mm f11 guidescope with my 130 f6 refractor and a 160 f3.3
Newtonian (Tak Epsilon) and it works very well with both. I put the
guidescope on one side of a Losmandy side-by-side plate and the imaging
scope on the other side. I frankly don't know what your dealers are talking
about in terms of "aligning" the guidescope to the imaging scope. As long as
your guidestar is within a degree or two of the target, you should have no
significant field rotation. There is certainly no sense in trying to
optically align the guidescope with the celestial pole or anything else. The
mount is what has to be aligned, and you should do that with the imaging
scope, NOT the guidescope. I would suggest getting a pair of good heavy
rings of the Losmandy type (I use 125 mm rings) and Losmandy plates, make
sure every thing is snugged down good and tight, and stay with the refractor
guidescope.
Hope this helps....
Bert

Bert Katzung
katzung1@home.com
www.astronomy-images.com

----- Original Message -----
From: "Aike M. Voelker" <AikeM.Voelker-Jamin@t-online.de>
To: <astro-photo@seds.org>
Sent: Friday, October 05, 2001 12:51 PM
Subject: [APML] guidescope / setup question


>
> Hi APML,
>
> after selling my LX 200, I am working on my new sepup for
astrophotography.
>
> My first decision regarding the primary scope was to go for a fast
Newtonian, a
> Vixen R200SS, it's a 8" f/4 (800mm focal lenght) telescope.
>
> The second decision to be made was (is) the guidescope. I've recently
purchased
> a Vixen 80mm / 1200mm refractor, which I thought would be a perfect
guidescope!
> I'm planing to get myself a EQ6 (expected delivery by the end of October),
which
> is a mount that carries up about to 35 pounds and is said to be as
dependable as
> the G11, but for a much more moderate price...
>
> But....
>
> After talking to some of my astronomical dealers, I've discovered that
they see
> a big problem in aligning the guidescope to the photographic scope. (The
> guidescope would be about 25" londer than my main instrument).
>
> Furthermore, I've received the advise that I should go for a smaller
guidescope
> such as the Meade ETX in order to prevent flexure, alignement problems of
the
> complete system.
>
> Here are my questions:
>
> - is anyone operating with a system comperable to mine?
> - if so, what are the expieriences with it?
> - how about the alignement of the two scopes when out in the field (I
don't have
>   a permanent setup, so I need to setup the whole stuff every single night
I
>   am photographing!)?
> - what kind of guidescope "brackets" are useful to ensure proper accuracy?
> - is the ETX a useful guidescope (mirror shift?)??? - I have read bad
things
>  about using a ETX as guidescope.....
>
> Any hints will be highly appreciated ,as I can't wait to get out in the
field
> again.
>
> I definatly don't want to loose "Clear Sky" time (very rare in the last
while
> anyways....), with a system that won't work at all.
>
> Thanks for any input,
>
> Clear Skies,
>
> Aike
> http://www.astrophotography.de
>
>
>
>
>
>
>
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