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Old 04-10-2018, 08:43 PM
Filippo
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Join Date: Sep 2018
Location: Melbourne
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Dew shield / heater for Celestron Nexstar 4SE

Hi all.

Just got this as my first telescope. I hear a dew shield is essential for this Mak so Iím looking to get one. I was thinking about the AstroZap combined dew shield & heater. Iím sure itís probably overpriced...but Iím not interested in making my own or anything. Iíd just like to know if they do the job and where to buy them (or similar).

I also have the Celestron Lithium 7Ah power tank. Anyone know if Iíll be ok running the scope and the dew heater for a few hours?

Thanks for any help.

Phil
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Old 05-10-2018, 06:42 AM
RyanJones
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Join Date: Jun 2018
Location: Melbourne,Australia
Posts: 619
Quote:
Originally Posted by Filippo View Post
Hi all.

Just got this as my first telescope. I hear a dew shield is essential for this Mak so I’m looking to get one. I was thinking about the AstroZap combined dew shield & heater. I’m sure it’s probably overpriced...but I’m not interested in making my own or anything. I’d just like to know if they do the job and where to buy them (or similar).

I also have the Celestron Lithium 7Ah power tank. Anyone know if I’ll be ok running the scope and the dew heater for a few hours?

Thanks for any help.

Phil
Hi Phil,

I have/had the exact same OTA as you. Before you spend your hard earned money on a heated dew shield. I have used this scope in the country to early hours of the morning and down to sub zero temperatures with nothing more than a plastic/cardboard shield. Effectively just a light sheild extending a couple hundred mm past the end of the OTA. By all means if you want to go down the proper dew heater direction then that's up to you just popping in my 2c worth congrats on your purchase and enjoy

Just noticed your profile lists you as 9km from me. I'll give you my old one if you like now that I'm using a C5.
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Old 05-10-2018, 09:10 AM
Wavytone (Nick)
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Join Date: Jul 2008
Location: Killara, Sydney
Posts: 3,697
Hi Phil,

You won't need a heater, there are better passive solutions. Dew forms when the corrector is allowed to cool below the dew point and there are two ways to prevent this. The old way was to apply heater straps, which ignores the real issue - that a metal OTA loses heat fast. The second solution is to add some insulation that stops the OTA cooling down - this is sufficient to keep the corrector above the dew point, and no dew.

There is another benefit too - larger maks and SCT often are affected by in internal air current that arises while the OTA is cooling. By insulating the OTA you’re blocking the flow of heat that causes this, and the result is the internal tube current is eliminated.

A simple dewcap made from just about anything will make a significant difference and it also cuts the amount of stray light entering the OTA, which improves contrast, particularly when look at objects near the moon. a piece of foam plastic and an elastic band - even string will do to hold it in place. If the dewcap extends down over much of the OTA that will do the trick very nicely. Here’s the one I use on my much larger mak - and it is fine at a cold mountain site where the temps fall below zero https://www.cloudynights.com/topic/6.../?fromsearch=1

Coreflute is available in black 2.5mm sheets for a few dollars, in case you’re wondering.

Last edited by Wavytone; 06-10-2018 at 10:49 AM.
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