Orion FlexiShield Dew Cap

5.0 Simple, Inexpensive Dew Prevention

Simple, inexpensive, effective.

May not be long enough for maximum effectiveness.

I recently bought a small Maksutov-Cassegrain telescope because I was interested in the compact size and portability. Living close to the water as I do, however, humidity is routinely high. This can cause a dew problem very familiar to users of Cassegrain telescopes which have optical corrector plates mounted only a fraction of an inch from the front edge of the scope's tube.

Dew shields are the simplest method of preventing this condensation so I purchased Orion’s FlexiShield for 90mm Maks. Selling for $14.95 (plus shipping, of course), I couldn’t resist.

The FlexiShield is a flexible rectangular sheet of ABS plastic with simulated leather/vinyl on one side and black, non-reflective flock on the other. It is wrapped around the front-end of the scope with the flock on the inside and is designed to extend 3-inches (76.2mm) in front of the scope’s corrector plate. A Velcro strip holds the shield closed and a rubber pad along the back edge holds it firmly in position.

I’ve heard it recommend that the distance a scope’s dew-shield extends in front of the corrector plate be at least one and a half times the corrector plate’s diameter. Though the FlexiShield falls short by about 2 ½ inches, it was effective at keeping my scope’s corrector plate dry on a moderately humid night. I can’t say if it would be as effective on a very humid night but neither would it be a good night for observing anyway. The FlexiShield is also good for preventing stray light from entering the scope’s tube from the side, something that badly degrades image contrast in many commercially made compound scopes that don’t have the internal light baffling that better scopes have.

In conclusion, Orion’s FlexiShield dew shield is effective at controlling dew on Cassegrain scopes at a good price.