cooling fan

[hes not well again]

I seem to have become confused about how one would use a primary cooling fan. I can see it would be handy for clearing the front of the mirror of any heat haze but surely if it were on when actually observing the slight vibration would hardly be good for pin sharp focus. Is it actually for cooling down scopes faster before use. The mirror cell on my scope is actually two brake shoes from a car bolted to a piece of ply [not my work] and collimation is difficult to say the least. As I will be replacing it I am in two minds as to whether to include a cooling fan. What are you experiences?

[Moonshane]

I use a cooling fan mainly to do just that, speed up the cooling. I don't usually observe with it on. vibration is not an issue as I fix mine with foam between the faffle and anything fixed on the scope that might transmit vibration.

I'd certainly recommend on as they do help with cooling a lot.

you need a surprisingly small fan to be effective. I have a single 80mm fan on my 16" mirror and it works a treat.

[Robert Watson]

I to have cooling fan's on both my scope 10"dob and 6" Tal and they are worth having. Both fans are 4" and they clear any haze mist of in a few min's, vibration no prob's

[umadog]

I leave my fan running the whole time. If they are well mounted and of a low-vibration design then they will not induce shaking. Some people do install fans in front or to the side of the scope, but most only install rear fans.

[hes not well again]

Thanks for that, is it possible to use computer fans as they are cheap and easy to get hold of.

[umadog]

Those are indeed what people use. Aim for a low-noise model as, chances are, this will also be low vibration. You can suspend it behind your mirror using three or four elastic bands. These will damp down vibration. I prefer to power it using a 12V deep-cycle battery. There are a number of reasons for this:

1. You can use it to power other things, such as dew-heaters.

2. If used carefully they will go through many, many, recharge cycles so not wasteful.

3. They come in a wide variety of sizes. The smaller ones are nice and compact. It's not expensive to get a battery which will power all your needs for very long periods.

[hes not well again]

Yes I was thinking of something like a car battery,plenty of amps availlable! Slung under the tripod would make it more stable.

[umadog]

Yep, exactly. Just make sure it's deep-cycle. Car batteries aren't deep-cycle since they're designed to produce large currents for short periods. They get terribly upset if you subject them to repeated discharge and recharging.

[angusb1]

Usually the deep cycle batteries are sold as "leisure" batteries.