Homemade Dew Prevention--Mylar?
Posted 29 September 2009 - 05:58 PM
I got to thinking (dangerous as it may be; it happens)...what would happen if I just bought one of those reflective Mylar "emergency blankets" you see in sporting goods stores like Gander Mountain and cut out a layer and wrap it around the scope? Has anyone tried this?
Posted 29 September 2009 - 06:24 PM
Even so, unless an extension is added to your dewcap, the IR flux radiating from the objective into the cold night sky will be as great as ever, and hence dew formation *may* be delayed for a bit. The best bet, in lieu of active heating, is to extend your dewcap by about double its current length.
Instead of a mylar blanket, how about a thin layer of some foam-based material. This is easier to work with in that it's perfectly OK to have it in contact with the 'scope. And it will probably better hinder dew formation on the objective than would mylar, whether with or without a dewcap extension.
Posted 29 September 2009 - 08:04 PM
Posted 30 September 2009 - 07:46 AM
Posted 30 September 2009 - 08:57 AM
Posted 30 September 2009 - 09:49 AM
Posted 04 October 2009 - 09:21 AM
So, you do not need nor want Insulation, nor do you want to prevent Radiation to the ground. What you do want is to prevent Radiation from the Top Side of your scope to the cold sky, and you do want Radiation from the warm ground to your scope underside. So, just cover the top half of
your scope with Mylar film, which is readily available on the internet. I believe mine was intended for indoor gardening. The prevention of radiation is very efficient.
I have a steel tube reflector, so a few small magnets keep it in place. For a non-magnetic tube perhaps a rubber band on each end and a cord wrap in between would do fine. Or you could epoxy a magnet inside at certain
spots to attract an outside magnet.
Please get a Radio Shack non-contact thermometer that senses Infra-Red. You will be amazed at the indicated temperature difference when you point at a cloud, the clear sky, the ground, and the underside of foliage. It has
endless other uses in finding weak insulation in the house wall, frozen spot of a water pipe, a hot semiconductor on a circuit board, proper pancake skillet temperature, etc. You will want to cover any highly reflective surface with dark masking tape, or whatever to get a good reading.
Otherwise you will only get the temperature of a reflected object.
Good Luck, Gene
Posted 03 December 2012 - 12:57 PM
Posted 03 December 2012 - 01:41 PM
A while back I picked up some NiChrome wire from eBay that can be plugged directly into a voltage source to generate heat. Just wrap it around the scope anywhere you want with tape or velco etc. I had it on a guide scope and even put it underneath a corrector plate on one telescope.
The amount of heat it gives off depends on the length of the wire and the rated wire resistance. Shorter wires get hotter (less resistance).
Different niChrome wires have different resistance per given length, so you need to figure out how long a wire you need and then determine the appropriate resistance. I know there's websites out there that can be googled with the details for resistance calculations.
Hope that helps.