Anonymous
Unregistered
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Hi,
I've just purchased my first CAT, a Nexstar 11 GPS XLT, and want advice on fighting dew/frost on cold Minnesota winter nights. Should I get a Dew Zapper or a foam shield, or can they be used together? I'm going to get the Celestron Power Tank 17 so juice shouldn't be a problem. Any advice or tips on cold weather viewing will be appreciated.
Thanks, Brett
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bierbelly
Postmaster
Reged: 01/23/04
Posts: 5434
Loc: Sterling, VA
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I think you'll need both.
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12" DSH
8" f/4 Vega MakNewt
6" MN66
TV85
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Ken....
Pooh-Bah
Reged: 01/22/04
Posts: 1005
Loc: Nashua, NH, USA
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They can, and probably should, be used together.
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Ken....
Discovery 10"
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Anonymous
Unregistered
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Sounds good, that's what I thought. I've been looking at Dew-Not-Dew strips on Scopestuff and they want you to order by tube diameter. Does anyone know the tube diameter on a Nexstar GPS11 since mine hasn't arrived yet and I can't find the spec on the Celestron site?
Thanks, Brett
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wilash
Fairy Godmother
Reged: 09/30/03
Posts: 5746
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Brett, it depends on how cold and humid your site is. I have found a dew sheild sufficient.
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Rusty
Postmaster
Reged: 08/06/03
Posts: 16406
Loc: Brooker, FL
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Quote:
Sounds good, that's what I thought. I've been looking at Dew-Not-Dew strips on Scopestuff and they want you to order by tube diameter. Does anyone know the tube diameter on a Nexstar GPS11 since mine hasn't arrived yet and I can't find the spec on the Celestron site?
Thanks, Brett
The DN012 should work fine. Fitting Dew-Not strips to the tube isn't critical, as they have a long strip of velcro, and an elastic strip.
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N11GPS Fastar
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Sometimes I think we're alone in the universe, and sometimes I think we're not. In either case the idea is quite staggering. - Arthur C. Clarke
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gazerjim
Postmaster
Reged: 02/12/04
Posts: 7726
Loc: About where I thought I was......
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Dewing has been a major problem for my 9.25 in humid central Texas. I need to check out those strips. Scopestuff happens to be about 5 miles from where I live.
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Jim Fisher
If you're not part of the solution, you're part of the precipitate.
Henry J. Tillman
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imjeffp
Senior Space Cadet
Reged: 09/30/03
Posts: 4430
Loc: Cedar Park, Texas
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So why hasn't Kendrick made an electric dew shield? Imagine something like an Orion Flexi-shield with an integrated heater strip on the scope end.
Or did I just give away my chance to cash in on the lucrative telescope accessory market?
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Blog
ST80 • AT80EDT/LXD650
ETX-90/DS-2000 • 10" LX200 Classic ("The Quarter-Meter Telescope at the Heritage Park Observatory")
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Rusty
Postmaster
Reged: 08/06/03
Posts: 16406
Loc: Brooker, FL
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I have two vintage Tuthill, one No-Du shield and one No-DU II - with built-in heaters. It's a supurb idea, well-executed, so why someone else hasn't done it (Tuthill No-Dus having been OOP for years) is beyond me...
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N11GPS Fastar
TOA-130S
MK66 Std
Vintage C5
Megrez II 80mm ED Triplet APO
SolarMax 40
NJP Temma II
Sirius EQ-G
ST8XE/CFW-8(LRGBHa)/AO-7/DF-2/STV Dlx/ST237a/350D (Unmodded)/Mallincam Color Hyper Plus/DSI III Color/DSI II Pro
Two not-spoiled Golden Retrievers - Maggie and Casey
Sometimes I think we're alone in the universe, and sometimes I think we're not. In either case the idea is quite staggering. - Arthur C. Clarke
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jrcrilly
Refractor wienie again
Reged: 04/30/03
Posts: 22469
Loc: NE Ohio
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Quote:
I have two vintage Tuthill, one No-Du shield and one No-DU II - with built-in heaters. It's a supurb idea, well-executed, so why someone else hasn't done it (Tuthill No-Dus having been OOP for years) is beyond me...
I like the Tuthill No-Du-Kap a lot; they are felt-lined. I'm pretty sure that Astro-Zap is now selling a shield with integral heater but I haven't seen or used one.
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John C
Urban Observatory
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ST-10XME
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imjeffp
Senior Space Cadet
Reged: 09/30/03
Posts: 4430
Loc: Cedar Park, Texas
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I see here where it's been done. Drats. I guess I'll have to go to work Monday.
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Blog
ST80 • AT80EDT/LXD650
ETX-90/DS-2000 • 10" LX200 Classic ("The Quarter-Meter Telescope at the Heritage Park Observatory")
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Anonymous
Unregistered
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Just how big a problem is dew with an SCT?
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Don W
Postmaster
Reged: 05/19/03
Posts: 13236
Loc: Wisconsin, USA
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An SCT's optics are right out there in the open. The corrector plate has no protection from dew at all. Even the slightest amount of dew will ruin your night. You need a dew shield or heater (both in Wisconsin) to keep it dry.
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Don Wyman
Obsession 18" f/4.5 #1166
W/Argo Navis DSC and Torus Primary
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celestial_search
Carpal Tunnel
Reged: 11/18/04
Posts: 2285
Loc: Iowa, USA
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Brett:
I live just south of you in NW Iowa. My dew shield for my C-11 SCT is still backordered. I bought some large pieces of black poster/construction paper and formed a dew shield around my C-11 and fastened it with scotch tape. I then wrapped an outer layer of mailing bubble wrap sheet around that and taped it. My homemade dew shield has worked for well over an hour in temps down to 20 degrees so far. I also made a dew shield for my finder scope that works well.
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Frank
C-11 XLT
8" f/6 Newt on GEM
Tak FS-102II
SV 80L Triplet APO
Orion Mak 127mm
EQ-6 Mount on pier in backyard observatory
CG-5 AS (GOTO)
Surveyor's tripod/Hercules single-arm alt-az mount
SBIG ST-5C CCD and Canon Digital Rebel XT
Oberwerk 15X70s and Pentax 10X21s
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AZDeepSky
sage
Reged: 09/19/04
Posts: 344
Loc: Tijeras, NM
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Brett,
Trying not to repeat what's been said, here's two small points based on my experience with the C11NS and as a pilot:
1. The dewpoint is a critical figure...for flying and observing. You can find the magic number on almost any good weather site. You can also figure it out by hand. In any case, that's when the wet stuff forms and settles. Definitely not a good time to have your scope pointing up, your paper charts and precious books laying open, and your laptop keyboard exposed! 
And of course glass radiates heat. So the corrector tends to accelerate the moment that the wet nasties might come. But I keep my scope in an unheated space. Thus corrector plate temp = atmospheric temp. Which minimizes the wet nasties.
Moral to this story: anticipate the dewpoint and the wet nasties. Keep your scope at atmospheric temp. And avoid having the scope pointed up when the wet nasties first form!
2. Although Flagstaff is usually dry, in the winter we can have some fierce wet nasties. Snow on the ground and sunny days often gives us high night time humidity and dewpoints in the 20-25 degree F range. But I've found that my Astrozap dewshield, plus avoiding the magic moment when the wet nasties come, to be sufficient.
But it's an empirical question. The Astrozap is pricey, but I've been totally satisfied. No additional equipment has been necessary. Except I've had to air dry a few star charts. 
Cheers.
Max
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Tak-Epsilon-180ED f/2.8
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imjeffp
Senior Space Cadet
Reged: 09/30/03
Posts: 4430
Loc: Cedar Park, Texas
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Quote:
Thus corrector plate temp = atmospheric temp.
Not always. Since the corrector also cools via radiation (and it's usually pointed at the cold of outer space), it will cool below ambient rapidly. All a dew heater has to do is to keep the corrector at ambient to prevent dew (assuming the dew point is below ambient).
Is there any correlation to snow or frost with the dew point being below freezing?
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Blog
ST80 • AT80EDT/LXD650
ETX-90/DS-2000 • 10" LX200 Classic ("The Quarter-Meter Telescope at the Heritage Park Observatory")
SPC900NC • DMK21AF04 • Digital Rebel XT
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Anonymous
Unregistered
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Thanks for all the replies! My scope arrives tomorrow and I have heater strips for the eye piece and corrector plate and my flexible dew shield should be here today. The forecast for the next 2 days is for temps around 0°F during the day and -8°F to -18°F at night. Right now the dewpoint/frostpoint is -15°F. I don't think dew will be a problem but freezing my you know what off will be! I am a little worried about bringing the scope back indoors when I'm through for the night. I'm thinking of 2 stages. First into the 25°F garage with dew strips still on for about an hour, and then put the scope into a cloth bag with corrector plate pointed down and bring it into the house. I'm a little worried that it will get soaked when I do this. Any thoughts?
Thanks, Brett
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AZDeepSky
sage
Reged: 09/19/04
Posts: 344
Loc: Tijeras, NM
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Brett,
why not just leave the scope in the garage? That's where I keep my C11. I set it on a rug, and put a garbage sack over it. My present garage is full of furniture,while we wait for our house --- I mean my new observatory location, but don't tell mama --- to be finished. And it's uninsulated. So it's close to outside temp.
One of Herschels speculum mirrors cracked in extreme cold. But they were made of metal. Glass mirrors are a different story.
Cheers.
Max
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Tak-Epsilon-180ED f/2.8
SV-115 f/7 TMB design
CGE x 2
SBIG-ST-2000XCM x 2
Canon 40D x 2
TV-.8FocalReducer
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Anonymous
Unregistered
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When I'm going to use it several nights in a row I'll keep it in the garage. However, due to the times we live in I don't trust keeping it there all the time due to the possibility of theft. Maybe some day I'll be able to build a small observatory shed on a secluded dark sky site we have and keep it there. Until then it will be in and out of the house.
Brett
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Anonymous
Unregistered
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You're right about theft but it is still the best place to keep the scope. I would only move it into the house if I was going to going away for a few days. Try not to advertise the fact that you even have that scope by using it in a spot that is not visible to passers-by. Definetely not in the front driveway.
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