Last updated: 31 July 2000

Homemade Dew Cap

From: Michel (jdcjdr@skynet.be)

Here is what I have done for the condensation problem. Please correct and modify any english mistakes before publish as you know, english this is not my mother language. Thanks for that.

dew cap I live in Belgium. Belgium is where all the air flows from atlantic ocean, siberia, sahara meet. This cause many frontal systems to croos the country and this is why Belgium is propably one of the more humid country. For astronomy this is not specially what we like to have on the Etx front lens so, I planned to buy a vapor shield. I went to several belgian dealers and no one has that for the Etx size. So I decided to make one myself. After several tries, I have find a perfect solution, cheep and efficient. May be your visitors will be happy to know how to make one.

I have buyed a camper matress. You know those very cheep one made of foam of about 5 mm. This cost about 2 dollars. Since I have not found a black one, I took the darkest possible : dark green. Next step was to cut the matrees in a way to make a Etx diameter + 5 cm cylinder with it. Then, an automobile mat paint spray was used to make it black. After that, I just glued some Velcro and that's it. The Velcro were those one used for automobiles. They are a bit stronger than others. Mike, this is just perfect ! I live in a big forest which increases the humidity. To give you an idea, without protection, the front lens is covered with vapor in a maximum of 10 minutes. With this protection, I have spent the whole night without any problem. The front lens remains clear of condensation. The effect is increased by the foam which slowly absords humidity. This is much better than a plastic foil. And to make the bonus point, it's light. Mine weights around 60 grams.

You will find here a picture. It's on my Etx 125 and you can clearly see the Velcro tapes.

dew cap

Important : after paint, let it dry a few hours and then, wash with clear water before to mount it on the Etx. This is to remove the dust created by the paint spay. Don't forget that or you may find the paint dust on the lens. In fact, I am not sure about the necessity to paint it. I made my tests without paint and it was perfect. This kind of foam is a little bit granular and this avoid light reflexions but we like to make it perfect is not it ?

Michel ( in Mons - Belgium )

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