[John K]

Hi everyone,

I am trying to design some type of cooling unit for my scope to speed up how quickly my full thickness 12.5" f/5 mirror cools down.

I have challenge ahead of me as the scope is a JMI NGT 12.5".

For those not familiar with this type of telescope, it's a truss mounted Newtonian, on a horseshoe equatorial mount (see pics attached). It's an excellent design, but does not come with a cooling fan! however the design does allow for lots of cool air to circlate very easily around the mirror. Being of all steel construction, it looses heat very quickly as there is no tube and so far I have used a domestic fan to simply blast the mirror with cool air.

The mirror is enclosed in a steel tub and there are 3 large counter-weights bolted to the back of the mirror cell holding it to the tub. There is no room to have anything extend past the counterweights as this would hit the horseshoe drive/gear.

So the challange is how to get cool air behind the mirror without having to completely rebuild the rear end which would require extensive metal work and could possibly jeoperdise the design of the telescope.

The only two ways that I could think of, is to place 2-3 fans simply on the inside side walls of the steel tub so as to create circulation in the tub area. I would make these units removable in order to remove the mirror tub if required. I have seen this design used in some large truss dobsonians, with fans placed in the inside square corners of the rocker box.

The other radical idea I have is to use 1/2 inch tubing to somehow pump cool air under the mirror cell and surrounding area. So I would need a unit of some sort that generates air and that I can simply plug into these tubes that could get air around and behind the mirror cell. Has anyone heard of anything like this? A small compressor of some sort perhaps to generate high pressure air?

Lastly, I could drill a few holes in the steel tub in locations that would not jeoperdise the stuctural integrity of the scope, however, this is once again a passive cooling method.

Images attached, so if you can put your thinking hat on and offer some suggestions that would be great!

Look forward to comments.

John.