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Fan Question...

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#1 Scanning4Comets



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Posted 17 November 2012 - 10:43 AM

Hi there!

I have a question regarding fans at the back of a reflector.

I have a large computer fan mounted on very stiff cardboard and painted flat black. I have it on the back of my mirror cell with elastic bands to hold it there. I can remove it when I need the scope to dry off after observing sessions if I need to, so no problems there.

I used to have the fan on my mirror cell with just elastic bands, which was also fine, but then I had read somewhere that a cover over the back of the cell plus the fan added on was better.

The only pain is having to constantly REMOVE the cover with the fan on it in order for my scope to dry off after observing. I'd rather have just the fan suspended in mid air facing the mirror so it can dry off better after sessions without having to remove the cover every time I bring it in.

Do you think it is better to have a fan plus a cover over the cell? Or is the fan suspended on elastic bands work just as good?

I'd really like to know which is better and I would prefer the "elastic bands with fan suspended in air" mode better so my mirror + scope can dry off better after sessions.

What do you guys think?


#2 Scanning4Comets



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Posted 17 November 2012 - 12:47 PM

I just found the answer myself in another thread I found! It looks like I will be keeping the back on there with the fan and I will be adding a ring baffle inside of the tube to deflect air over the boundary layer! :jump:

I have a ring baffle all ready to go.

#3 Mike B

Mike B


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Posted 17 November 2012 - 12:57 PM

Hi Mark-

I use just the suspended fan alone on my smaller 6" tuber Newt... while i haven't compared baffle/no-baffle, the solo fan seems to work far better than NO fan. And i can actually feel a notable breeze at the *top* of the tube, so i KNOW quite a bit of air is makin' its way up the tube- doin' the work! Have you checked this on *your* scope?

But this may be less critical on a smaller mirror, like mine's, where the ratio of fan *size* + air volume pushed vs. mirror size is greater; i'd imagine that, with a smallish PC fan blowin' at the back of a 10-12" disc of Pyrex, MOST air would be bouncin' back & goin' NOwhere; a baffle there should accomplish much in directing the air past the mirror & up the tube.

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