[ATM] Mirror Cooling Fan

[Jay Kirkland <jaykirk2@compusmart.ab.ca>]

    A couple years ago, I finished re-building my 12" and placed a pair 
of computer cooling fans, ~2" in diameter, blowing across the face of 
the primary. The fans are mounted directly onto the 5/8 baltic mirror 
box. Even at top speed and high mag, there is no trace of vibration, but 
the scope is a typical wooden Kriege/Berry dob, very solid. I have also 
added the foam dust filters that match up with the computer fan, and 
over the exit holes I use self-adhesive velcro to hold thin black 
humidifier filter material in place - it makes an excellent dust and 
light trap.
    When the fans are turned on, the effect on seeing is both immediate 
and startling. I have never seen planets as clearly in 20 years of 
observing. Last year Saturn looked like a cardboard cutout handing in 
the fov. When the fans are turned off, the seeing immediately 
degenerates, no matter how long I've been using the scope. The 12" is 
full-thickness, and I don't know long it takes to reach equibrilium, or 
if in fact it ever has. I don't have any fans blowing on the back of the 
mirror, tho I keep thinking I should experiment with that, too.
    Jay

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