Quote:
Originally Posted by mental4astro
There is a different take on this today when it comes to SCT's and Maks.
Instead of having the scope cool down, DON'T let it cool down!
The problem of heat in an SCT and Mak is the metal or carbon fibre tube cools down quickly, but there is a big thermal mass inside the OTA - the glass mirror and baffle tube. So what happens when the tube cools, a heat plume is generated inside the OTA. This means that if you want to use your scope after setting up, you may need to wait anywhere from an hour to several hours depending on the temperature differential between the scope and night time temperature, and also the size of the scope.
By not letting the scope cool it is done by insulating the OTA. Insulating the OTA, the heat plume is prevented from being generated, meaning that the there is no need for a cooling period for the scope and it can be used at high magnification as soon as it is set up. Of course, the scope is still cooling down, but it is the rate of cool which has been dramatically altered, there by preventing the heat plume to develop.
I have been insulating my SCT's and Maks for several years now. I use these scope from home where I don't have time to set up and wait for two to three hours for the scope to cool down. I will typically only have two to three hours with a scope, and pulling one out is next to always a spare of the moment decision. Then certainly there is no time for waiting for the scope to cool down. Yet by insulating these closed tube instruments, I can crank them up to 400X as soon as it is set up - the only caveat is the prevailing seeing conditions - and no time lost to a cooling period.
There is an added bonus to insulating an SCT or Mak - it helps keep the corrector plate dry from dew for longer.
Insulating the OTA won't necessarily prevent the corrector from dewing up, particularly an SCT corrector as it has so little mass to it. My backyard sees more nights with heavy dew than dry nights. I have had both my insulated SCT's and Maks dew up on some night when conditions were especially heavy. I have also come up with a way of keeping my SCT's and Maks dry regardless of dew - by installing a small 12V fan into the side of the dewshield end of the insulating wrap. No need to use heating straps for dew control as heating straps add the very thing we have been striving to avoid - heat.
You will find more information on insulating SCT's and Maks and the use of a fan here:
SCT & Mak total dew control without heat - a solution!
The first pic below shows the insulating wrap I made from an old yoga mat for an SCT. The second pic shows a naked 7" Mak, then the same Mak with its wrap made from Coreflute. The last pics show the small 40mm fan installed into the side of the dewshield end of the wrap.
Alex. |
Thanks Alex.
Getting 400X straight away is very impressive indeed.
A bit problematic with the tube rings on my MAK, but doable on my SCT.
I tend to just put the MAK or SCT in my carport hours before using it in early hours of the evening - then having dinner, watching news and current affairs - before finally getting around to viewing many hours later (or cursing because it's gone cloudy in the meantime.)
Cheers,
Renato