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Tubes for Reflecting Telescopes

Started by brucesdad13, 01/27/2015 09:58PM
Posted 01/27/2015 09:58PM Opening Post
Nice article here: I found the section on tube color very thought provoking.

~ Charlie Stevenson

8" f/5.7 String Telescope - 1st Scope Build; 2nd Place Stellafane 2016 Optical Award for Newtonians 12.5" and Smaller
10" f/4.5 Newtonian (June 2015) mirror refigured by Optic Wave Labs P-V WaveFront 1/14.24, Strehl Ratio 0.993 (Aug '15)
Criterion RV-6 seems to be circa 1973 (June 2015) [For Sale]
Celestron C8-A XLT (January 2015) [For Sale]
Celestron PowerSeeker 70AZ (Christmas 2014)
Aldrich Astronomical Society member since 2015
Posted 01/28/2015 04:01AM #1
I added a BIG muffin fan to my 12.5 and would suck air down thru the tube for an hour before use (air filter over front end!). I experimented with a star image and even knife-edge during cool-down and the effects were very interesting to watch! The mirror had objectionable spherical aberration that would completely go away over about an hour. And sometimes fan on was better, sometimes fan off...depending on conditions. the fan (and scope and mount) were so good that fan on introduced NO vibration in the image! So I could toggle it on and off looking for effect. At (rare) times the scope would present little Airy Disc (= half arc-sec resolution!) if the atmosphere allowed. My best scope for CONTRAST was a 17.5" full tube I lined with sheet cork and then Black Velvet (measured BB diffuse R = 0.4%). Friends would actually comment on the great contrast without my asking. I think contrast is the most commonly unaddressed issue with most scopes...especially portable ones. Those ultralight minimalist Dobs are especially vulnerable. Tom Dey

29-inch Dob in a dome
36-inch upgrade soon
LUNT 80/80 solar scope
FLI 6803 cam
APM 100mm APO Binos
JMI RB-16 Night Vision Binos
Zeiss 20x60 IS binos