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Astrozap dew shield


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From photos I've seen on the Astrozap site, these are being used like big lens hoods on the front of the scope. I would have expected it to go round the body of my scope (NexStar 6se) like an insulating blanket. How is it supposed to work?

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No.

It does two things:

- Stop extraneous light getting in from the sides

- reduces the opportunity of dew "dropping" onto the front lens

The heater is positioned close to the front lens and in theory should just apply enough warmth to keep its temperature above the dew point to discourage dew forming.

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The dew sheilds are used as you have seen - effectively extending the tube to prevent dew from forming on the optical elements at the top end of the tube. Here is another SGL thread on this which includes a link to a photo which may help:

http://stargazerslounge.com/equipment-help/94316-keeping-dew-off-6-reflector.html

Actually you don't want to insulate the tube - you need the warm air in it to radiate away (some through the tube walls) as quickly as possible.

Dew shields also act as light shields which keep stray light from entering the top of the tube, reducing contrast.

Edited by John
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I have one and they are great! You realize how great they are when early hrs of the morning you see frost 3" down the inside of the dew shield. With out the dew shield that frost would be on your objective lens or secondary mirror. Another plus is on reflectors your secondary is close to the tube opening which with out a dew shield would be susceptible to stray light.

SPACEBOY

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