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Wes James
Post Laureate
Reged: 04/12/06
Posts: 3453
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Continuing my questions on accessories for the new C8 that's being delivered tomorrow- I need to order a dew shield and heater strip... would it be advantageous to order a dew shield with a built-in heater strip- or a seperate dew shield and heater strip? Opinions please?? Thanks!
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Wes
Atlantic Beach, FL
Some bino’s from Miyauchi 5x32 Binon's up through Garrett 20x110 Signature's,
Some telescopes from a Stellarvue 80mm NHNG up through a couple of 8” reflectors…
And a wonderful 4.25" Delmarva Shiefspiegler!
Some good friends, made here on C/N.
Oh- several cats and a wonderful wife!
Anyone want a cat???? :-O
"When your work speaks for itself- Don't Interrupt" -Gamble Rogers
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letimotif
No Complaints
Reged: 05/20/07
Posts: 2010
Loc: Far Flung Isles of Langerhans
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The challenge with the combo models that incorporate the strip into the shield is that if the strips gives up the ghost you have a really expensive dewshield. Also, you don't always need the strip, so you've got to find a home for the cord when it's not in use.
I know some folks appreciate the convenience, and this combo version has its proponents. It's just that, for me, having the two separate makes more sense from an economic and convenience standpoint.
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Ah, but a man's reach should exceed his grasp, or what's a Heaven for?
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Lane
Carpal Tunnel
Reged: 11/19/07
Posts: 1507
Loc: Frisco, Texas
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I would keep them separate it gives you more options on placement of the heater wire. For me the dewstrip often works best when it is positioned further back. I actually wrap the one on my C11 around the grey part of the tube and under the dovetail. Even it you don't put it that far back you will still probably want it further back than is possible with the combo device. Plus there are many nights, especially with the C8, when a dewshield is all you need and you can leave the wires in a box.
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Mounts: CGEM, ORION SIRIUS, AT Voyager/motorized
SCTs: C6, C8, C9.25, C11,
Refractors: TV Pronto, Orion ED80
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Wes James
Post Laureate
Reged: 04/12/06
Posts: 3453
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Your comments make good sense.. thanks for your replies. I just wanted to see how others approach the idea of the two. Thanks again~!
Wes
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Billydee
super member
Reged: 01/23/08
Posts: 184
Loc: Winter Haven, FL
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Goto http://www.kendrickastro.com/astro/dewcap.html This one page has the info on a standard shield and two types of heated shields and way to add a heater strip to the standard one.
Might help, Bill
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davidpitre
Carpal Tunnel
Reged: 05/10/05
Posts: 1824
Loc: Central Texas
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Quote:
For me the dewstrip often works best when it is positioned further back. I actually wrap the one on my C11 around the grey part of the tube and under the dovetail.
Agreed. The combo heater/dew shield often is heating the end of the optical tube and is not positioned around the corrector. Very inefficient.
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David
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GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1267
Loc: Ottawa, Ontario, Canada
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Actually, it's not necessarily inefficient to have the heat source located within the dewcap. Here's why.
Wrapped around the corrector cell (as most folks do), one is striving to conduct heat from the rim inward through a large area, thin plate of glass. This is inefficient.
With the heater located a distance in front of the corrector, it can radiatively 'bathe' the corrector more uniformly with IR, offsetting that radiating from the glass and out into the heat sink of the cold night sky. For this to work most efficiently, two details should be attended to:
- Wrap the outside of the dewcap with a thin layer of insulating material. The heater will warm the cap itself, and why allow some of the precious heat to needlessly escape through its outer surface?
- Install a kind of 'backwall', resembling a baffle ring, immediately skyward of the heater (this assumes the heater is a relatively narrow wrap of 'wire' on the *inside* surface of the dewcap). Its clear aperture must of course be no smaller than that of the scope's corector. This backwall serves to reflect back some of the IR which would otherwise radiate directly out to the sky.
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces
My Gallery
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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skybsd
professor emeritus
Reged: 02/01/08
Posts: 599
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Hi,
I have both options in use across my SCTs.
I have AstroZap heated dewshields as well as AstroZap Aluminium dewshields + dew strips.
I see no difference in performance - never had a problem with my corrector dewing up on any of my SCTs.
Regards,
skybsd
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