From: "Scott Berfield" 
To: 
Reply-To: "Scott Berfield" 


With so little clearance between tube and mirror, your biggest problem will
be air turbulence from the tube wall. For a 5" mirror a 1/4 inch
clearance all around just isn't enough room for proper air flow. I would
want at least an inch all around if possible.

-----Original Message-----
From: owner-atm{at}shore.net [mailto:owner-atm{at}shore.net] On Behalf Of
Dennis Woos
Sent: Thursday, June 12, 2003 2:34 PM To: atm{at}shore.net
Subject: ATM Tube Question


My young son Tim (11 years old) and I are making a 5" f/11.4
newtonian. We have acquired a .8" secondary, a very low profile
1.25" helical focuser, and a 5.5" I.D. sonotube.  Our three
remaining challenges are to 1) get the mirror coated with a short
turn-around, 2) build a secondary holder and spider, and 3) decide on the
tube.

Our concern on the tube stems from its small diameter, and concerns that
stray light will reflect off of the tube walls and enter the optical path.
We are concerned that even ProtoStar flocking paper will not prevent this.
However, we do want to stay as close to the secondary as is reasonably
possible, as he wants a planet scope with small secondary.  Will the
flocking paper do the job?  If not, we can use the 5.5" tube at the
top end to mount the secondary and focuser, and then step up to a larger
diameter tube (we have some 8").  What do folks think about the tube
issue?

How about a quick coating - any good sources?

And finally, I have make seconday holders and spiders, but never one this
tiny.  Any Ideas?  Thanks.

Dennis

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