On the stock installed fan, you wouldn't notice much acutely because the fan as installed just blows air against the back of the mirror, which then bounces back and away. Very little acutally goes up the sides of the tube, and almost NONE goes across the face of the mirror, which is where this boundary layer is. The stock fan will just help drive the mirror's temp down which helps, but it takes time...it's just speeding mirror equilibration with ambient. While there are many ways to address this, if you store your mirror where it'll be closer to ambient normally, it's probably not worth the effort. Or, put a box fan up against the back of the scope for the 30-45 min while you are setting up and waiting for dark. That's what many with big dobs (stored inside) do to drive the mirror temp down and minimize these effects.
This phenomenon is much more noticed in the very large mirrors (18" and up). My 12" cools down fairly quickly, but on my 18" the fan set up really helps esp in the 1st 1-2 hours of the night...unless the mirror was at ambient already.
I'd agree with Gargoyle_Ste tho, that collimation issues are MUCH more likely - across a broad range of users - to be an issue than tweaking temperature issues in these scopes.
s
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Originally Posted by mrsnipey
Whoa, haven't been on in a couple of days and there's a few more posts than there was before.
I finally turned the fan on the other day. Sorry to say that I didn't notice any difference (other than Jupiter which seemed to be perfectly clear - no change in ngc's).
I think you might be right Gargoyle_Steve. My collimation might be off. I'm in the process of saving up for a laser collimator at the moment.
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