Quote:
Originally Posted by ninja2
I don't think this make any diff - the ETX-90 is a Maksutov-Cassegrain. From Wikipedia this looks to be very similar to the Schmidt-Cassegrain. Can't all telescope designs accumulate dew?
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Dew is a problem for all telescopes, but SCTs and Maks are especially vulnerable due to their glass face plates. Refractors tend to come with with dew shields and open reflectors (like a classic newt) have one effective built in with the primary being all the way down.
Dew heaters are a pretty comprehensive solution, but expensive. They also mean more cables and fiddling around if you are just doing a quick viewing session.
To me they are over the top for most visual astronomy. Good if you plan on going all night out at a dark site, but at home there are cheaper options that are still effective.
For a start I suggest making a dew shield (foam plus Velcro is a great suggestion). It won’t prevent dew for ever, but it’ll keep it at bay for several hours. A big difference for a mak that doesn’t come with one!
The other great solution is the humble hair dryer. When dew starts forming on that front plate, warm it up with the hair dryer and problem solved. Essential this works the same as using a dew heater (same idea, keep the glass above dew point), but you probably have a hair dryer and an extension cord at home already.