Homemade Dew Shield

Although I don't have a lot of trouble from dew here, probably thanks to the dew heater I made, a nice dark shield helps to keep a lot of stray light out of your scope. It also helps reduce the power required if you're running a heater too. Eventually, I may bite the bullet and get one of those fancy aluminium ones, but for the moment I'd rather spend my cash on other accessories. I therefore built my own flexible dew shield, as detailed here.

The basis of the shield is a foam insulation mat, which is usually used for sleeping on when camping. You can find them in camping/outdoor stores, but be prepared to shop around for a black one, which will reduce the amount of light reflected into the aperture. Mine coincidentally had a blue outer layer - not exactly a match with the Meade OTA, but not a complete co-ordination disaster either.

If it's a simple dew shield you're after, you could simply cut out an appropriate chunk and tape it into a tube shape. The foam is elastic enough to stretch a little, allowing easy removal and replacement. I however decided to make a fastening system using Velcro strips - one around the circumference where it will meet the OTA, and one to hold the ends together to form the tube shape.

The main reason for using this method of attachment was that I wanted to combine the shield with my homemade dew heater. This can make fitting a pain - the heating elements are quite thick. I ended up trimming a strip of foam away into which the elements fit so that the foam remains tight against the end of the OTA. I then covered the elements with some good old duct tape - one strip level with the back of the shield, then one curled around the back and onto the outside of the shield. It helps to keep the shield roughly cylindrical when taping to avoid stretches or wrinkles in the tape.

Cross-section of the rear end of the shield, showing the heater element.

A Velcro strip along the length of the tube holds the shield's shape.

A self-adhesive Velcro strip runs around the back of the shield which allows a tight, stretched fit around the end of the OTA. Another strip runs along the length of the "seam" where the two ends meet. One half is stuck to a flap made from (you guessed it) duct tape. For a picture of the shield in action, take a look at my LX90 page.

In the long term, I found that the Velcro strip didn't keep the dewshield as round as I'd have liked. I therefore fixed the majority of the length with duct tape, leaving a short part open which could be tightened down with the Velcro around the base of the shield. I also went back to a separate heater strip and dew shield set-up, as pictured on the main LX90 page. This is definitely the way to go if using counterweights or extra mounting bars on the scope, as the heater fits further back, allowing the shield to fit better.