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Les
professor emeritus
Reged: 04/22/06
Posts: 730
Loc: Maryland
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Quote:
Dew caps work by limiting the area of cold night sky into which the optic can radiate its precious heat.
Yes, dewing is due (sic) to a radiative process not conduction (unless you view in the tropics and take your binos out of an air conditioned house). I suspect the small mass of the thin Canon window also contributes to the quick dissipation of heat that gets the surface temp below the dewpoint. Now if we just would keep those optics pointed at the ground we could solve this problem, but then we wouldn't see too many stars that way.
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Les
Canon 10x42L IS
Oberwerks BT80/45, Helix Hercules mount on Oberwerks Standard Tripod
Swift 8x44ED Ultralite
Questar 50th Anniversary Model, 501 head on Manfrotto 475 tripod
Stellarvue SV90T 90mm Fluorite refractor Bogen 3236/Televue Tele-Pod Head
Questar 7 Astro
Vixen GP-DX on Baader Surveyor Tripod
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DJB
Carpal Tunnel
Reged: 02/23/05
Posts: 1589
Loc: Lisle NY
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Hi all,
I am from the old camp, and I always protected my expensive camera lenses with a UV or 1A filter, usually a HOYA brand.
Many in the camera field DO NOT want anything over their precious camera "objective." I do not agree, however.
Although, on two occasions, a filter has saved my butt. This is only my personal advice.
Best regards,
Dave.
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14724
Loc: Cumberland, R I , USA42N71.4W
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Quote:
Quote:
Dew caps work by limiting the area of cold night sky into which the optic can radiate its precious heat.
I suspect the small mass of the thin Canon window also contributes to the quick dissipation of heat that gets the surface temp below the dewpoint.
That's the main point. heat transfer across a thin lens mass means the outer surface of the thin lens gets warmer quicker then the outer surface of a thick lens.
FWIW, I would find taking the binoculars off target to stick them under my coat impractical. To many times during the night, I either move to another instrument, to either compare views or compare instruments, reference a chart, write down some notes, etc. Taking the binocular off the target would then mean the need to re-acquire the target would become a repetative activity of the night. Somtimes it takes 5 to 10 minutes just to acquire the target, not something I'd want to keep repeating.
I suppose sticking them under your coat is reasonable if you are using the binoculars as a finder scope. I've done that with other binocs when I was at my scope and wanted to keep the binocs close at hand. But then, in those cases, I'm not binocular viewing.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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NoiseJammer
super member
Reged: 09/16/07
Posts: 181
Loc: Gone walkabout
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I've tried a pair of lens hoods on my 10x42 IS binos - I found that there wasn't really enough thread available to allow them to screw securely onto the enternal thread. Otoh, I do think that a pair of sacrificial filters are an excellent idea! Many years ago, one saved my butt on an expensive zoom lens.
Clearest
Bruce, Toronto
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178 square inches of mostly shiny glass, one biph
... and way, way too much light polution.
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GaryS
super member
Reged: 10/30/06
Posts: 191
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Quote:
FWIW, I would find taking the binoculars off target to stick them under my coat impractical. To many times during the night, I either move to another instrument, to either compare views or compare instruments, reference a chart, write down some notes, etc. Taking the binocular off the target would then mean the need to re-acquire the target would become a repetative activity of the night. Somtimes it takes 5 to 10 minutes just to acquire the target, not something I'd want to keep repeating.
edz
Yes, clearly tucking them under your coat isn't practical if the binos are mounted -- I was making that suggestion in the context of image-stabilized binos, which you take off target every time you stop looking to consult a chart or make notes.
As an aside, I find that once I know my route to a given target, reacquiring it takes only a moment after the first time. Of course, everyone will have a different take on whether or not this is going to soak up too much time in an observing session, but it certainly can add up. That's one of the advantages of mounted binoculars. Of course, if your binos dew up, it's going to take time to get the lenses clear again, so something's got to give. As I said, for my part, I find the best strategy is to avoid the dew in the first place -- and that's where the under-the-coat trick works well as a preventative measure.
The bottom line in all this is if you have dewy conditions, don't just leave your binoculars lying around in the open! If tucking them under your coat isn't practical, take a towel out with you and throw that over the binos when they're not in use (mounted or not). That'll at least help a bit.
Gary
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Sky & Telescope Contributing Editor
SkyNews Columnist & Blogger
www.GarySeronik.com
A place for stargazing enthusiasts.
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14724
Loc: Cumberland, R I , USA42N71.4W
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Quote:
If tucking them under your coat isn't practical, take a towel out with you and throw that over the binos when they're not in use (mounted or not). That'll at least help a bit.
that's a trick I use often.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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