Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

Reply
 
Thread Tools Rate Thread
  #21  
Old 02-09-2013, 02:46 AM
dp297 (Dimitris)
Registered User

dp297 is offline
 
Join Date: Jul 2011
Location: Athens, Greece
Posts: 26
Quote:
Originally Posted by peter_4059 View Post
Ray - can you comment on the success of the aluminium tape to prevent dew formation?
That would be nice to know...
Reply With Quote
  #22  
Old 02-09-2013, 06:09 AM
Shiraz's Avatar
Shiraz (Ray)
Registered User

Shiraz is offline
 
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,787
Quote:
Originally Posted by peter_4059 View Post
Ray - can you comment on the success of the aluminium tape to prevent dew formation?
Quote:
Originally Posted by dp297 View Post
That would be nice to know...
As far as I know, Anthony Wesley pioneered the idea of low emissivity for amateur scopes (in Australia at least) by using unpainted aluminium tubes for his planetary scopes.

I did some measurements and confirmed that GSO painted steel would drop well below the ambient air temperature due to radiative cooling from the cold sky - which is a lot colder than ambient at the zenith (maybe -40C). That can overcool the air around the tube and turns the scope into a dew magnet - just like the roof of a car. Rather than build new OTAs, I wrapped the existing tubes with adhesive aluminium tape - tried flashing tape and aluminised ducting tape from Bunnings - both worked OK, although the duct tape is much lighter in weight.

Aluminium has low thermal emissivity, so the scope tube does not cool as much through radiation and stays much closer to the air temperature. Dew is less of a problem, although the blackened interior of the OTA and other parts of the scope still drop the temp a bit up the front end. Definitely works though - I have only had two occasions where dew was a problem in the past couple of years - everything around the scope can be wet, but the ota will generally still be relatively dry.

Don't know how it would go on anything but a Newtonian - something with glass up the front will get cold, since glass has high thermal emissivity and it will generally be pointing close to the zenith. I guess that is why dew shields are needed on SCTs and refractors - they restrict the amount of cold sky that the glass can "see". It would probably still help though if the tube itself did not cool below ambient, so aluminium tape might be beneficial.

An emergency thermal blanket or aluminium foil can be easily wrapped around things if you want to experiment and are concerned with what your scope looks like. Al tape is pretty permanent and looks daggy after while - it is soft and ends up with dings and scuff marks in normal use. I view a new GSO scope as a starting point and don't care too much what it ends up looking like, but it might be different for a Tak owner, who will probably have paid more for the paint than I pay for a complete scope.

regards ray

Last edited by Shiraz; 02-09-2013 at 12:38 PM.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 09:47 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
NexDome Observatories
Advertisement
SkyWatcher Australia
Advertisement
Celestron Australia
Advertisement
Lunatico Astronomical
Advertisement
Meade Australia
Advertisement
Bintel
Advertisement
OzScopes Authorised Dealer
Advertisement
Astronomy and Electronics Centre
Advertisement