Newtonian secondary mirror DEW prevention.

[John Hothersall]

Hello IIS I am in UK waiting to emmigrate to Oz but here in UK my new Orion Optics 14" Newt made with Aluminium tube gets misting/ice on secondary on cold nights within an hour, with Newts I have not had this before and am putting it down to Aluminium tube loosing heat at the top more quickly.

I have ordered small Dew Not strap to put around secondary mirror cell stem which draws 3watts 0.25amps to see if this will help, I also have a foam dew shield I made myself but shielding 14" newt is difficult.

I may have to order 14" Dew Not strap to wrap around optical tube if the small heater strap does not work here in UK.

I just wondered what degree of dewing in humid Brisbane would I expect with an open tube newtonian. Will dewing in Brisbane be more of a problem for me than here in the UK.

Thanks JohnH.

[bmitchell82 (Brendan)]

I don't belive that it will be that much of a problem as the temperatures don't get extremely cold and once more there isn't that much humidity in brisbane in the winter time.

[toryglen-boy (Duncan)]

Originally Posted by John Hothersall

Hello IIS I am in UK waiting to emmigrate to Oz but here in UK my new Orion Optics 14" Newt made with Aluminium tube gets misting/ice on secondary on cold nights within an hour, with Newts I have not had this before and am putting it down to Aluminium tube loosing heat at the top more quickly.

I have ordered small Dew Not strap to put around secondary mirror cell stem which draws 3watts 0.25amps to see if this will help, I also have a foam dew shield I made myself but shielding 14" newt is difficult.

I may have to order 14" Dew Not strap to wrap around optical tube if the small heater strap does not work here in UK.

I just wondered what degree of dewing in humid Brisbane would I expect with an open tube newtonian. Will dewing in Brisbane be more of a problem for me than here in the UK.

Thanks JohnH.

As a Brit, that moved to Australia a couple of years ago i thought i would answer.

you will be fine.

that is all

[JethroB76 (Jeff)]

Extending the upper OTA with a light/dew shield can be quite effective. However, I (and several others on IIS) have installed Astro-System secondary heaters which fit inside the secondary holder and attach to the back of the mirror itself - very effective.

I would be surprised if you didn't experience some dewing in Brisbane

[erick (Eric)]

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[RobF (Rob)]

I've only dewed up once in Brissy - and it was 3am towards end of winter. Low tech solution has been working since then - a thin piece of camping foam formed into a 12" cylinder I pop on the end of the scope. If you block "line of sight" between an object and the heavens its a lot harder for IR energy to escape such that object (2ndary) is cold enough to dew.

p.s. Most Brissy folk worry they're going to freeze to death below 10 degrees celsius....

[mrsnipey]

I think I dewed up on the same night as you Rob. First and only time.

[lesbehrens (Les)]

my 16" 2ndry does dew up. i too am looking to fix that up. i have thought about putting a heater around the 2ndry. that should work.
les

[GrahamL]

Don't think you will have much of a problem john with the mods your
adding to your scope ..I was mostly barefoot a couple of years back observing through winter.. sure the odd cool night and sometimes a bit of dew but its never been often enough to make me do anything about it.

cheers good luck with the move

[Jooster]

I use a battery powered hot air blower. Works a treat