RE: [APML] 8" Reflector decent enough for prime focus AP?

[Rex Moore <RMoore@fool.com>]

Thank you all so much for your input... extremely helpful (though I am
disappointed, of course ;)).


I'm sort of scratching my head right now because I just can't go over $600.
So I may have to buy this Orion anyway. I'll certainly try some piggybacking
now and then, and even an occasional prime focus if it's not *totally*
impossible, but I definitely know not to expect much. Again, this will be
mainly for visual use.

Thanks again, you guys are great...

Rex





-----Original Message-----
From: Torsten Clay [mailto:tclay@theriver.com]
Sent: Tuesday, March 12, 2002 1:10 AM
To: 'astro-photo@seds.org'
Subject: Re: [APML] 8" Reflector decent enough for prime focus AP?


On Mon, 11 Mar 2002, Rex Moore wrote:

> The introductory email said all levels of experience are welcome, so I
hope
> you don't mind a question from a rank beginner!
>
> This Orion SkyView Deluxe 8 EQ Newtonian is about at the limit of what I
can
> afford to purchase right now:
>
http://www.telescope.com/cgi-bin/OrionTel.storefront/3c8d7c3a03724cb02719c0a
> 80a6506d5/Product/View/A319
>

I can see a few potential problems:

1) the focuser is 1.25", which is not big enough to fully illuminate the
film. You will get a "porthole" in the middle of the frame.

2) even if you replaced the focuser with a 2" model, the secondary mirror
is going to be too small to fully illuminate the film

3) you might need to move the mirror forward to get the camera (especially
if you use an off-axis guider) to focus. Usually not hard to do

4) the mount is going to be a little weak for prime-focus work

5) you will really want a coma corrector at f/4


Another option is to forget prime-focus for the time being, and do some
wide-field piggyback photos...you will likely get much better results and
many fewer headaches!

Torsten



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