Cooling 190mm Mak-Newt

[karpana]

I live in Central Canada, and as you can well imagine winter is in full-swing. I've recently purchased a 190mm Mak-Newt and like all my scopes, it is kept indoors when not in use. Unfortunately, with the meniscus, I'm finding that the optics are taking a while to cool down. A lot longer than I had anticipated considering the temperature differential, which these last few days has been on the order of 35 degrees celsius, but will be much higher as annual 'deep freeze' sets in (occasionally bordering on 50 degrees differential)

The mak-newt has brackets behind the primary mirror for installing an 80mm fan, but I'm concerned about how to cool the scope down without causing/injecting too much particulate/dust in the optical system.

My thoughts for cooling were to mount an 80mm fan behind the primary, and install a second fan on the eyepiece holder to draw cool air through the scope (up from the primary and out the focuser) in an attempt to prevent settling of any dust or other airborne debris on either the primary, secondary or back side of the meniscus. Unfortunately, but I'm not sure if this is a good idea or not.

Wondering what others have done to help cool their 'sealed' scopes (although my specific concern is mak-newt's).

Looking forward to hearing back.

Thanks,

Paul.

[ollypenrice]

Firstly could you not take it out ahead of time?

Secondly, if you left it orientated with the focusser pointing up and no EP in, warm air would be allowed out. You might worry about dust so maybe a fine mesh filter over the hole as a compromise?

Olly

[beamish]

TBH that's all I do ! If it looks like I'll be out, I stick it on the mount and connect up the fan and just let it run until it's dark and I go out or the clouds come across and it all comes back in

[karpana]

Although I do take it out to cool in advance, I'm finding that the time between "I want to go observe, so let's put the scope out" and "I'm ready to observe", is only about 30-40 minutes.

This duration was plenty fine for my 150mm newt, but doesn't seem to be doing the trick for the mak-newt.

[beamish]

No, TBH it won't be and that is the price one pays for owning a Mak, planning is key. However once that sea-change is achieved, cool down time no longer is an issue- bottom line is that a Mak , whether it's Mak Newt or Mak Cass will never be a "grab and go"

[karpana]

Is there some way of ball-parking the cool down time (eg. minutes/degree)?

[nightfisher]

here`s what i do, 2 scopes so i leave the mak to start cooling and have the evostar on the mount, then when im ready i swap evo for omc job done

[beamish]

I've never really thought about it but in general if I plan for an hour whilst doing something else -all's well, but when I'm sure of conds I'll set it up and start the fan ASAP, so absolutely no concerns over thermal plumes once I go out and the kids are in bed

[John]

My 6" mak-newt needs around 60 mins to cool from house temperature to outside at this time of year. It was a little quicker in the autumn months. A standard newtonian is going to cool quicker because i) it's an open tube design and ii) the tube walls tend to be thinner than on mak-newts.

I follow the Olly / Karlo approach which seems to work - I can use low / medium power after 20 mins or so. I don't have a cooling fan fitted at the moment but it's something I'm considering.

I've always understood that maks / SCT's would need more cooling time than other designs - it sort of "goes with the territory" so to speak.

I don't think I'd consider a closed tube design, with the exception of a refractor, if I lived somewhere prone to really cold nights - where I live (SW UK) -5 C is considered a pretty cold night.

[beamish]

Umm, lets face it the awfully cold spell we're experiencing right now is just that , a cold spell.

The only other suggestion would be to have a locked and bolted down cabinet outside of the house where the scope may be kept far closer to ambient , ( in cases where an obsy isn't feasible)

[Mr Spock]

I put my OTA out as soon as I get home from work. By the time dinner has been cooked and eaten, e-mails read etc, it's plenty cool enough to use.

[ollypenrice]

I did a piece in the Nov issue of Astronomy Now on a watercooled Newtonian. This is outside the scope of what most would want to do! However, what about using physiotherapy gel packs from the freezer, maybe placed against the lower end of the OTA and/or on the tube cover with the scope vertical? Warm air rising to the top of the tube will heat the corrector and this heat might pass easily into the cold metal tube cover. If the cover is not metal, make a metal one...

Olly