Telescope Reviews: Bigger Cat = more dew

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Equipment Discussions >> Cats & Casses

Pages: 1

Kon Dealer
professor emeritus

Reged: 01/05/11

Loc: Cambridge UK

Bigger Cat = more dew new

#5615126 - 01/10/13 09:41 AM

I have a 4" refractor, plus a 6SE and an 8SE.
All have "regulation" length dewshields.
The 4" NEVER dews up, the 6SE occasionally and the 8SE almost always.
(Which is one reason the 8SE never goes to a dark site- I can't use my wife's hairdryer on it!)

Is this usual?
What is other people's experience of this?

Post Extras:

bcuddihee
Carpal Tunnel

Reged: 11/04/06

Loc: Cincinnati Ohio

Re: Bigger Cat = more dew new

[Re: Kon Dealer]
#5615169 - 01/10/13 10:10 AM

Get a dew heater and fit it under the shield. Also they do mahe 12v hair dryers.

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bcuddihee
Carpal Tunnel

Reged: 11/04/06

Loc: Cincinnati Ohio

Re: Bigger Cat = more dew new

[Re: Kon Dealer]
#5615170 - 01/10/13 10:10 AM

Get a dew heater and fit it under the shield. Also they do mahe 12v hair dryers.

Post Extras:

GlennLeDrew
Postmaster

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada

Re: Bigger Cat = more dew new

[Re: bcuddihee]
#5615675 - 01/10/13 02:49 PM

For one thing, the Schmidt corrector is very thin for its diameter, and so cools more rapidly. How do the diameter-to-depth ratios of each dewcap compare? To reduce the cooling rate on the exposed optic, the longer the dewcap relative to its diameter the better. The idea is to present to the optic a minimal area of sky into which to radiate.

Notwithstanding the above, for those jaunts away from AC current sources, best to invest in active heaters powered by a battery.

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Sorny
super member

Reged: 03/15/12

Loc: Southern MN

Re: Bigger Cat = more dew new

[Re: GlennLeDrew]
#5615859 - 01/10/13 04:43 PM

Yeah, the bigger the scope, the faster it dews up.

Get a dew-heater & controller. I don't need active dew prevention on my C5, but my C11 requires it.

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WadeH237
scholastic sledgehammer

Reged: 02/24/07

Loc: Snohomish, WA

Re: Bigger Cat = more dew new

[Re: Sorny]
#5616361 - 01/10/13 09:59 PM

You should see how fast a C14 dews up

If used properly, a combination of dew heater with dew shield should be 100% effective at keeping things clear. I have a Keating dew heater, which regulates the temperature based on an offset from ambient. I run mine about 5 degrees above ambient and it keeps things clear even on the most humid of nights. The trick is to have the dew strap wrapped around the OTA just behind the corrector (ie. not around the edge of the corrector itself).

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dobsoscope
sage

Reged: 05/24/06

Re: Bigger Cat = more dew [Re: WadeH237]
#5616425 - 01/10/13 10:41 PM