[ATM] cooling fan dust/light filters

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

    After following the thread on the physics of quartz fusing itself 
together, this seems like an embarassingly elementary contribution to 
make but...
    It's been at least a year since the S&T articles on cooling fans 
blowing across the face of the primary, and since I instantly adopted 
the idea for my scopes. What always bothered me was the holes in the 
mirror box that let in stay light and, worse, dust. I tried a variety of 
things and then when I was building a new computer in December 
"discovered" that any computer shop sells washable dust filters for 
standard size computer fans. These just clip into the top of the fan and 
are perfect for keeping dust and stray light out of that side of the 
mirror box. You can also get great looking brass grills for covering the 
fan holes. So I set out to find something to filter light and dust from 
the exhaust holes in the top of the mirror box. Honeywell sells a 
Universal Replacement Pre-filter for their hepa air cleaners. It's thin, 
reasonably opaque, very dark grey, about 1 1/2 x 3', about $10, and 
easily and securely attaches to the inside of the mirror box using the 
hook half of velco tape. One package did my 5 scopes.
   

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