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Troubleshooting FAQ | Problems? PM a Red or a Green Gu.... uh, User
Hrundi
super member
Reged: 02/06/08
Posts: 118
Loc: Estonia
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I was out, seeing the perseids, and took my scope with me as well. While initially it was good, it quickly started to show halos around stars, and this got progressively worse and worse. Focusing became harder and harder. I'm guessing this is all the dew's fault. By the end of the session, the refractor had dewed up so badly, I didn't see any stars. The pleiades was blank sky, and jupiter was the faintest of dot in the eyepiece.
The refractor has a dew shield, which was up for the entire night, and probably gave me whatever viewing I got.
My question is, how do I fight this? By the end of the session, the laptop I brought with me felt like it had taken a swim, and the cars windows had zero visibility, so this is some serious dew I need to fight.
One option is, obviously, to wait until the temp hits sub zero degrees, but I'd rather prefer to go see the sky in months that are not february 
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edwincjones
Post Laureate
Reged: 04/10/04
Posts: 4429
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I use a small, battery operated "hair dryer" from Orion to blow dry the optics.
More expensive dew devises are available, the this seems to work best for me.
edj
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n w arkansas
Binocular, Solar, General Amateur Astronomy
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kaaikop
sage
Reged: 07/13/08
Posts: 468
Loc: Ste-Therese, Canada
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THIS is a little cumbersome (requires carrying a battery), but it will do the job!
I have had a few good nights ruined by dew very early on,
that is when I decided to get serious artillery.
There are other brands as well (just recommending Made in Canada) 
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Benoit, RASC Montreal
-C 9.25XLT on EQ6 Pro / ED80SF on Portamount
-Plossls, Radians, Naglers, LVW's & Orthos.
-a pair of 7x50's
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WNCAGC
sage
Reged: 06/25/08
Posts: 259
Loc: NC Mountains (God's country)
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A good old fashioned dew shield that you wrap around the tube works great as well for the most part unless you just have extreme case of dew ridden air.
Mine was $40 for my scope. I have toyed with the idea of a electronic system with dew strips but that would be a $100 plus system and for now the shield works.
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CPC 1100 XLT "The Big Monster"
Power Tank 17
NexImager
2" Smart Astronomy 10:1 dual speed Crayford focuser
2" Smart Astronomy Dielectric diagonal
2" Smart Astronomy 2x Barlow
2" Baader SCOPOS 35 mm prototype EP
Baader Hyperion zoom EP 8-24mm
Celestron dew shield
Bob's Knobs
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chug187
member
Reged: 09/18/06
Posts: 25
Loc: Bethesda, MD
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You have to combat dew at two places: your scope's objective lense, and your eyepieces. If either one dews up, you're cooked. Since you already have a dew shield, your problem was likely at the eyepiece.
Cover your eyepieces from the sky when not in use. When an eyepiece is exposed to the sky, it will radiate with outer space. Prevent this by keeping it covered from the sky as much as possible. I keep my eyepieces in a drink cooler, and I place the cooler under by observing table to further block it from the sky.
If the dew is really bad, toss a disposable hand warmer next to your eyepieces. The warmth from hand warmer should provide just enough heat to keep them above the dew point.
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Matt
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6" Meade Starfinder, EQ Mount
12.5" Obsession
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Midnight Dan
professor emeritus
Reged: 01/23/08
Posts: 620
Loc: Brockport, NY
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Sub-zero temperatures won't help. You'll just get frost instead of dew.
If your dew is that bad, you'll need some heat. As some here have suggested, there are hand warmers you can use.
A more sophisticated approach (in other words, expensive :-) is to use dew heaters. You'll need a 12 volt power supply, heater strips to wrap around your optics (eyepiece and objective) and a controller.
Most folks recommend the Dew-not brand heater strips, and the DewBuster controller. The strips can be had online for $20-$50, depending on size, the controller is about $130 (I think), and a 12V power supply is $50 to $100.
It adds up, but nobody said this hobby was cheap! On the other hand, all that money can buy a LOT of hand warmers!
-Dan
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Scopes: Celestron NexStar 8, Orion EON 72mm ED/APO on Astroview mount (EQ3)
Eyepieces: Celestron 40mm, 25mm, Baader Hyperion 13mm, 8mm, 5mm
Other: Telrad, 2x Barlow, 0.63x Focal Reducer, Dew-not strips, DewBuster controller
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stevek
Pooh-Bah
Reged: 04/16/06
Posts: 1229
Loc: west michigan
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I made dew shields for both my finder (the bigger problem) and for the DOB tube. When its really bad, I'll use one of those dispo hand warmers and a rubber band to add heat on outside of the finder. Running the cooling fan seems to be enough air disturbance to keep dew off the primary.
Steve
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DSO 8" f6 DOB w/ 8x50 RACI & 2"Crayford
1958 Sears Discoverer 76mm Refractor
GSO SV 30mm 2",21mm Hyp,13mm Strat,BO/TMB ver2-6mm & 4mm
1.25"Filters: DGM-NPB, 25%ND
1.25" plossls: 25mm,20mm,15mm,9mm
Orion 2X Shorty Barlow
Garrett Gemini LW 11x56mm binocs
BTG-10 4.0mW green laser pointer
"What is that burning in the sky? Tell me y'all..." Jeff Beck/Jan Hammer
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coutleef
scholastic sledgehammer
Reged: 02/21/08
Posts: 825
Loc: Montreal and St-Donat, Québec,...
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I am surprised you had Dew poroblems in Montreal. Where do you make your obseravtions?
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François
Nexstar 8 SE
50mm StellarVue finderscope, Astronomik UHC-E and Orion OIII filters
WO Swan 40mm; TV Pan 22mm; TV Nagler 9T6, 12T4, 17T4; TV Plossl 11mm and 15mm.
WO 2" dielectric diagonal retrofitted with Denk Power Switch (and now reach the zenith with the shorty adapter).
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kaaikop
sage
Reged: 07/13/08
Posts: 468
Loc: Ste-Therese, Canada
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Quote:
I am surprised you had Dew poroblems in Montreal. Where do you make your obseravtions?
You are joking, right? 
Actually I should ask "where do YOU make your observations?"
Most of the time from my backyard in Ste-Therese, or other astro-club related sites around Mtl.
I think it has more to do with the exteme "wet" summer we are having...
One evening a few weeks ago, I set up my stuff and by the time I was star-aligned and ready,
it was too late already, everything was smothered with dew.
I am not saying I actually need the Kendrick everytime, but I'm not taking chances anymore, I've got it, and it just works.
When you get an average of 1 or 2 good nights per month, I am not willing to let dew ruin my fun.
Of course, if I could find a "CLOUD BUSTER" somewhere, or at least rent one for my vacations...
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Benoit, RASC Montreal
-C 9.25XLT on EQ6 Pro / ED80SF on Portamount
-Plossls, Radians, Naglers, LVW's & Orthos.
-a pair of 7x50's
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coutleef
scholastic sledgehammer
Reged: 02/21/08
Posts: 825
Loc: Montreal and St-Donat, Québec,...
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Well, i make my observations in Montreal or St-Donat.
Up to now, never had any problem with dew (i obviously don't go out when it rains!).
My dew shield acts more to protect against unwanted light than to protect against dew.
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François
Nexstar 8 SE
50mm StellarVue finderscope, Astronomik UHC-E and Orion OIII filters
WO Swan 40mm; TV Pan 22mm; TV Nagler 9T6, 12T4, 17T4; TV Plossl 11mm and 15mm.
WO 2" dielectric diagonal retrofitted with Denk Power Switch (and now reach the zenith with the shorty adapter).
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w orchid
professor emeritus
Reged: 04/23/07
Posts: 677
Loc: Tampa, Fl
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Invest the money in a heated dew contoller with strips. You will not regret it.
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Celestron C8 orange tube circa 1982
Stellarvue SV102ED
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coutleef
scholastic sledgehammer
Reged: 02/21/08
Posts: 825
Loc: Montreal and St-Donat, Québec,...
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Up to now, i never had any dew problem. I do not think i will in fall.
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François
Nexstar 8 SE
50mm StellarVue finderscope, Astronomik UHC-E and Orion OIII filters
WO Swan 40mm; TV Pan 22mm; TV Nagler 9T6, 12T4, 17T4; TV Plossl 11mm and 15mm.
WO 2" dielectric diagonal retrofitted with Denk Power Switch (and now reach the zenith with the shorty adapter).
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JShrum
professor emeritus
Reged: 08/14/07
Posts: 734
Loc: Bay City, MI, USA
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Nothing worse than having a good night end short because of dew. I'd vote for the DewBuster and at least a corrector strip...other things can be capped off when not in use. They have saved more than one observing session for me! 
Clear Skies...
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Jeff Shrum
Bay City, MI
CPC 1100 XLT
WO 2" Crayford 2-speed Focuser
OPT 2" Dielectric Diagonal
Sunset Astronomical Society
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Snaproll
Post Laureate
Reged: 02/20/04
Posts: 3493
Loc: Wisconsin
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A couple other points that may be helpful. For finder scopes, I used snap-closed rifle scope covers (or just use the regular lens covers but you never misplace the others since they're attached). This helps keep the dew at bay on the finder, provided you remember to close them.
If your scope is not in use, point it horizontal and preferably cover the scope/eyepieces. A dish towel works well on the eyepiece area.
Dew heaters are the best way to go and worth the investment. A dew controller is a good buy too, but they need to be monitored to make sure they aren't putting out too much heat or too little. Too much and you're running the battery down and potentially getting tube currents. Once dew does set in, it takes a lot of heat to get rid of it. All you really need to do is keep the surface one or two degrees above ambient and dew won't form.
A good investment is a temperature sensing dew controller, but they are expensive, usually $150 or so. They control the heat and keep it at a constant setting as the night cools. They do the job but only use enough power to keep the dew off so they save the battery.
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-Jim-
Happiness is a clear sky and a Denk II
old AP images and some new C14 Hyperstar images
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