Fans on telescopes

[icytailmark]

i have seen many people put a fan on the end of their telescope and i was wondering why they do it?

[mithrandir]

To help the scope temperature to stabilise faster. You want all the components at a stable cool temp to produce the best performance. The airflow also discourages dew formation.

[icytailmark]

Where can i get a fan for my telescope? What battery can i use to power it?

I have a 12" SW collapsible DOB with an Argo Navis.

[DavidU]

A Newtonian telescope uses a large mirror, this is a weighty item and holds a lot of heat. A scope like this works better if the mirror is the same temperature as the surrounding air.
So to aid cooling the mirror down you can force air onto the mirror with a fan.
In reality even with a fan the mirror will almost always be a few degrees warmer than the surrounding air.
A warm mirror produces convection air currents in the tube and disrupts the path of light. Another thing is a "boundary" layer of warm air on the surface of the mirror that produces a mirage effect on it's surface.
I have found blowing air across the mirror surface and cooling it with a rear fan really sharpens up the image detail especially when viewing planets.
Hope this helps

[Rodstar]

Yes, it is best to get the mirror temp within about 2 degrees of ambient temp, or thermal currents will spoil the image. This is often confused with bad seeing. A fan will improve a mirror's cool down time, so early in the evening when the temp can drop very quickly a fan is rather important.

[mill]

Goto jaycar and get a 12V fan that you can stick to the mirror.
You can use a 12V battery pack or a 12V 17AH battery also sold at jaycar.

[DavidU]

I found it very easy to fit a 12v fan by 3 thick rubber bands to the body of the fan stretched to the 3 collimation knobs, the rubber bands also stop any vibration. I will get a pic of this.

[pmrid]

The answer depends a fair bit on your scope and your DIY skills.
Most scope fans are 12 volt DC so they would run off the same power supply as your mount. And most scope fans are little (if any) different from the kind of case fan that you fit to a computer. They'd need some sort of guard around them for obvious reasons though.

Some scopes come with the fan built in - such as the newtonians made by GSO. I suggest you go to your nearest scope shop and have a browse. You'll see how they are mounted and powered.

Peter