I use closed cell foam as a dew shield on my LX90 8" SCT. I usually have it sitting about 3 - 4" onto the OTA, almost to the fork arms. I didn't do it this way to intentionally insulate the OTA, it's just the way I installed it after I made it & the way I set it up each time to give the foam rigidity so that it doesn't collapse in on itself at the far end & restrict my light gathering.
Edit: actually looking at my scope, it's probably like 5 - 6" down the OTA, the piece of foam I use as a dew shield is 18" long.
Is this sufficient insulation to achieve what you are indicating below?
Or should I be looking to make some modifications to have it extend further down the OTA?
Cheers
Carlton
Quote:
Originally Posted by mental4astro
David, this is going to make your wheels spin! 
Instead of letting your Mak cool, rather DON'T let it cool!
The problem that cooling introduces is the metal tube cools quickly, leaving the air inside the tube to create a temperature gradient between the metal tube and the baffle/primary mirror, and this produces the tube currents.
By insulating the OTA, you don't allow the metal tube to cool too quickly, there by not creating a temperature gradient between the tube and the internals of the OTA, and hence no tube currents.
A few of us have started doing this to our Maks. The insulation can be as simple as a black yoga mat! And the rolled up mat is made such that it extends over the corrector lens just like a dew shield, making it duel purpose. And the result is immediate with no waiting time between set up to observing. This has been done from 6" Maks to 9" Maks.
Alex. |