[ATM] A coolingfan under a 12,5 inch

["Treur, Harro" <H.Treur@wlb.amsterdam.nl>]

Hello everyone,

I have followed the coolingfan-discussing lately with much interest.
John Sherman; thanks for all your efforts.
My primary is a 12,5 inch  - 2 inch thick. I want to place one coolingfan on
my telescope, and I understood that underneath is the best position. 

Question 1: my fan will be placed only 1 inch under the mirror. Doesn't this
fan create a local cold spot on the mirror, thus creating deformation?

Question 2: should the fan blow air up? Or should it pull the air down (In
my eyes, this should not create a cold spot)?

Question 3: my coolingfan is a small one (only 2 inches wide) so it won't
consume too much power. I understood from the articles in Sky&Telescope
(July 2004?) that even the smallest fan can do a good job. What do you
think?

Thank you and greetings from snowy Holland
Harro Treur




-----Oorspronkelijk bericht-----
Van: Jean-Guy Moreau [mailto:jgmoreau@cablevision.qc.ca] 
Verzonden: dinsdag 22 februari 2005 16:07
Aan: atm@atmlist.net
Onderwerp: [ATM] Recent work on 25 ins lightweight mirror


Hi,

Just wanted to share some recent results working
on a 25" F/4 mirror, this one hopefully
for my personal use  ;-)

overall view of the plate glass blank here :

http://www.cablevision.qc.ca/astro/25_may04_face.jpg


the mirror on its stand, supported only by the hole in the center of the
backplate :

http://www.cablevision.qc.ca/astro/25_stand.jpg

and the resulting foucault image after 4 hours polishing 
with a 14" lap on my machine,
stroke is lap starting edge to edge with mirror, to overhang
by about 25%, 20 strokes per minutes, table speed 10 rpm :

http://www.cablevision.qc.ca/astro/25ins_fev05_foucault.jpg

hope you enjoy,

Jean-Guy

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