I went to Hobby Lobby last week to buy a few sheets of 2mm thick black foam rubber. I found them in the children's education part of the store. I bought the foam to make a backdrop for my secondary on the ring structure of my new Looking Glass.
While I was there, I bought a couple more sheets to play with. Nearly simultaneously, Matt R. was there and working with the foam. He kindly made me a pair of dew shields for the Eyes of Texas, my 80mm binocular. He also cut a sheet for my Telrad.
From my scraps of Fun Foam, I built a simple wrap-around dew shield for my 50mm finder. I built it so that I could put a hand warmer packet inside the ring if I desired.
Last night, in my observing session at Hill Country State Natural Area, the dew was pretty heavy and early. (On the way home, there were blankets of radiation fog in every valley.) I had put the finder scope dew cover on and it kept that objective clear of dew all evening. I ended up needing to wrap a hand warmer around the eyepiece of the finder with a rubber band. that worked, but I was late in choosing to do this and had to deal with occasional dew on the eyepiece.
The Telrad cover was attached by wrapping rubber band around the long axis of the Telrad base. The cover was held nicely in place by the rubber band. This kept the Telrad remarkably free of dew without sacrificing the utility of the finder.
I was finally done in for the night at about 830 PM, two hours after I began to observe, by dew forming on my secondary. I forgot to bring my hair dryer for that. With a hair dryer, I would have been able to continue for a while longer, until fog formed in the observing area.
For just a couple bucks, these "throw-away" dew covers are extremely easy to make and work very well. Their outer surfaces were *covered* with dew by the time I packed up, but the optics were nice and clear.
sounds like you need a secondary dew heater huh? Well I'm glad you made use of the dew covers I made you.
ReplyDeleteMaybe a heater. Though the idea of using a hair dryer that heats up the reflective side of the glass sounds pretty attractive.
ReplyDeleteThanks for the dew shield that you made. It worked great. Thanks for the idea of using the material. The finder scope shield with internal heater pouch also worked like a champ.
When the Telrad finally was obstructed by dew, it was on the under surface of the glass, not the top surface like usual. Maybe it was from an errant breath with which I fogged the diagonal?
I look forward to your leading the SAAA in building some of these. They are pretty close to being as useful as sliced bread.