Re: ATM Ultra-Light Dobs mounts

["Chris Westland" <westland@uxmail.ust.hk>]

It's attractive to consider using the primary as the focuser.  You are
essentially putting the reticle off--axis slightly, and assuming you will
get an adequate focus at the plastic screen.

-c

-----Original Message-----
From: Nils Olof Carlin <nilsolof.carlin@swipnet.se>
To: Chris Westland <westland@uxmail.ust.hk>; atm@shore.net <atm@shore.net>
Date: Tuesday, September 09, 1997 1:03 PM
Subject: SV: ATM Ultra-Light Dobs mounts



>Chris & others
>
>> A giant Telrad could be made by mounting a desktop magnifier (US$ 5 in
>Hong
>> Kong for a 4" magnifying glass, with square mounting) on the mirror
>> cell/altitude bearings of the scope
>
>Come to think of it, there *is* already a big magnifier (20" maybe) already
>mounted, and ready to use! On the very first Dob mount I made for my
>Coulter mirror I had a finder consisting of a semi-reflecting glass (a
>camera skylight filter)mounted on the diagonal cage and a LED mounted
>diagonally opposite, shining down to the mirror (just missing the central
>spot), and reflected up to the glass.
>
>I drooped the idea temporarily, as I found out I needed the corner of the
>square diagonal cage for the focuser, but I think it would easily adapt
>itself to an ultralight open design (Mel, I have tried to read that page
>but only got a small piece of text.?).
>
>What you would need is a flat glass plate on an adjustable mount on the
>diagonal cage, a reticle mounted on the diagonally opposite side of the
>cage and lit by a LED (maybe a pattern with white on black, reflecting the
>LED). The focusing isn't critical, and I had no problem with the
>LED/reticle being a little closer than focus (with f/300 - 400 effective,
>coma is no problem, neither is remaining parallax). A battery (small 3V
>lithium for lightness), a pot for brightness and a microswitch to turn it
>on when in use, placed where you can reach it when you move the Dob.
>
>Nils Olof
>
>> You would have a giant, open, large aperture Telrad appropriate
>> for an Ultralight Dob ...
>>
>>
>