fan on the back of mirror?

[leedseagle]

Does attaching a fan on the back of the primary mirror of dobsonian telescope significantly cut cooling down times? As still getting watery images through Barlow

[Skystef]

Hi,

currently the temperature of outside is more or less the same as the temperature inside your home. So basicly it doesn't matter that much this season. So if you think this might cause some blur, this is not the reason. I think the main reason for blurry pictures are the heat waves, it only starts to diminish dramaticly somewhere in November. Season from Spring via Summer to Autumn, only a couple of hours after sunrise or before sunset are usefull, at least when using the barlow.

To come back to the question, it is certainly usefull in the Winter season. I too thought about using a fan near the mirror, I gave it up as you have to make some holes in the tube near the mirror, presumable posing a major dust problem. So my solution is that the fan blows from the top. When not making pics, I lower the upper part of (the open) tube and let the fan (which rests on the ground) just blow in from there. It seems to work too.

[leedseagle]

cheers stef a great help as always,
i've seen this Orion fan which my scope has holes for on bottom of the primary mirror
http://www.crazycameras.co.uk/index.php ... ff_code=gg

i thought it blew but as i have found on following link this Orion fan sucks air through the tube from the bottom seems good idea to me
http://tech.groups.yahoo.com/group/orio ... essage/659

What do you think?