From: "CSC" 
To: "Atm" 
Reply-To: "CSC" 


Wow! Have you got a nice scope there!  The testing info means you've likely
got a top notch planetary mirror. I'd say proceed and then star test it. 
By then you'll be enjoying it and won't care about the figure.  Probably
"beyond reproach" as Texereau calls it.

The old tubes were often thin sheet steel, with end rings.  A liner of flat
black painted cork sheet was often included in some early designs. 
Probably best to line a full tube. The metal can create sharp currents when
rapidly cooling down.

Recently I am appreciating the open tube for my own viewing.  Sometimes
requires a shroud to keep body heat out, but otherwise, I really like it.

If you can keep the whole lower mount light, rigid and smooth, it should work well.

Our club has a 10" f/10 that will get a workout this planet year.

Colin

-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net]On Behalf Of John
Murray
Sent: Sunday, December 15, 2002 7:32 PM To: Amateur Telescope Makers
Subject: ATM Long focal length advice required please,



G'day Everyone,
        A member of our group (Mick) has had the good luck to be given
an aluminised mirror from the widow of the person who made it. The chap who
made it was an active mirror maker many years ago and his widow would like
to see the mirror put into a scope. After testing it, I found the following
details

Diameter        230mm
ROC             4200mm!!

        This makes it approximately  a nine inch F-10 mirror!! After
allowing the mirror to acclimatise (24 hrs)before testing  we can see that
the surface is very smooth with very gentle ronchi lines. Getting readings
with the ronchi and foucault proved extremely difficult. The shadows moved
at the slight thought! of movement. Any suggestions for this?
        Mick and a mate who is a boilermaker are considering making an
Alt/Az based on ideas from Berrys book "How to make a Telescope".
Being a boilermaker though they are both looking at making the entire mount
from tubing and welding it. Any ideas on whether this would work or suffer
any effects due to being made from metal? I've thought of vibration and
weight so far but any thing else? They believe they can make it quite
light.

Cheers

John Murray
Whyalla
South Australia

--- BBBS/NT v4.00 MP