Re: ATM RFT wrinkles (fwd)

[behambu@ibm.net (Berthold Hamburger)]

On Thu, 3 Oct 1996 10:42:25 +0200 (MET DST), you wrote:

>
>
>---------- Forwarded message ----------
>Date: Thu, 3 Oct 1996 10:11:29 +0200 (MET DST)
>From: Wolfgang Birkfellner <birkfell@merlin.pap.univie.ac.at>
>To: etomlins@rohan.sdsu.edu
>Subject: Re: Re: ATM RFT wrinkles
>
>et wrote:
>>I've just checked out your design for a sliding focuser.  It's a 
>>good design; I like it, although I don't know that I want a
>>_motorized_ focuser.
>
>In my opinion, the sledge type focuser is not that great - the next 
>problem was that we had to stop breathing when we were looking into 
>the eyepiece. But this could be overcome by using a shutter or something 
>like that.

I am very happy with mine. I used only one threaded rod which is
mounted central on the sled. Instead of turning the rod, I turn a
wheel with a T-nut to move the rod for- and backwards. 
No need for a shutter. Just put a piece of black paper between sledge
and tube and oversize the sledge slightly.

As I mentioned before, I guess that there is a secondary size limit
for that kind of focuser. 
My expieriences with a 33mm flat are very good so far. I have not had
one single alignment/collimation problem with the focuser even though
focuser travel is 8 cm in both directions.

The advantages on the other hand are significant especially for a
small telescope, where it might be difficult otherwise to find a good
relation between a focuser height that allows also for photography and
a big illuminated field with a minimized secondary obstruction.
The reason I had to go for a 33mm diagonal was that I could not find a
smaller one. Otherwise I could have gone as small as 29mm or probably
even smaller.

Apart from that you can make a sled-focuser almost entirely of plywood
which makes it especially attractive for people who have no access to
a machine shop.

Berthold

                        -------------------
Mag. Art. Berthold Hamburger - Cellist
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