Which direction for fans on Dob fans

[Josh Wilson]

I just need a basic answer for this one. What direction does the air flow go for cooling fans?

[knobby]

I reckon it would work either way !

Sucking warm air away from the mirror or blowing cooler air onto it ...

[swamp thing]

Normally the fans blow air onto the back of the mirror. Others use fans to blow air accross the surface of the mirror, others still, use a combination of the two.

[jimmyjamjoejoe]

I saw an article a while back which suggested blowing air onto the mirror cooled it slightly quicker, but sucking clears the boundary layer much more cleanly so good observing can be done before the mirror is completely cooled. There really wasn't much in it though really, swings and roundabout.

[umadog]

To effectively suck off the boundary layer you would probably need seal the back of the scope around the fan and install a baffle around the primary: http://autocostruttori.blogspot.com/2009/08/yet-another-method-for-cooling-mirrors.html

Otherwise, you're better off blowing. This will cool the mirror faster. CPU fans blow too for the same reason.