Jump to content


Astrozap dew shield

Recommended Posts

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?

Link to comment
Share on other sites


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.

Link to comment
Share on other sites

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:


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
Link to comment
Share on other sites

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.


Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.