getting rid of dew

[richbyers]

whats the best way to minimise dew on a dob?

i dont really want to fork out on expensive equipment, but i cant think of any other way to get rid of it, and leaving the scope out to cool just get it soaked.....

rich

[M110]

Hmmm never actually had this problem myself but it should be fixable. Are you getting dew on the primary, secondary or both?

People have great success making dew shields out of foam camping mats for use on maks and SCT's don;t know if it works for a reflector but you could give it a go - might help and camping mats can be found for £3-4 if you look around.

If you know your way around a soldering iron then a secondary dew heater could be constructed from some resistors stuck to the back of the secondary with wires running along the spider vanes to a battery pack/power source outside the tube.

good luck,

Alex

[richbyers]

it gets on everything- im sure it must be an obvious mistake im making.

ill take it out to cool for 30mins then i come back and its covered

cheers

rich

[Bizibilder]

Are you getting this dewing problem at the moment? If so it could be that your scope is stored at a lower temperature than the outside dew point. Thus when you put it outside dew will form immediately as the scope is too cold NOT too warm! If the atmosphere is very humid - which it may well be in Cumbria - this may well be your problem. The solution is to warm the scope or to store it in a warmer place.

[Talitha]

Maybe it would help if it's under an overhang like a carport,

awning, or patio umbrella when you put it out to cool.

[richbyers]

ok cheers for the help guys

rich

[Moonshane]

hi Rich

when you cool your scope, are you pointing it at the sky (i.e. vertically)? this is a sure way to lead to dewing problems. I generally only point mine vertically when in use and when it's cooling / not in use always point down. I've not had any dob dewing problems but once left my refractor pointed up for half an hour and it was covered.

the same applies to eyepieces of course. always cover when not in use (again the camping mat can be used to make a small tube which should help.

[Bizibilder]

I forgot to put this in the post above as an example of how close the dew point and ambient temperature can be:

Today, on a dull wet (it keeps drizzling) July afternoon it is 21°C outside and 19°C indoors. The dew point today is 17°C. As you can see there is not much difference so it would be easy to have a scope that was below the dew point and thus would "dew up" as soon as it went outside.

[Mouse on the Moon]

I generally stick a bin bag over the scope when cooling and this seems to help. It's also stored fairly close to ambient which no doubt helps as well.

[Srbin]

If you do have to go down the dew heater route, I've found the Dew-Not heater strips from Modern Astronomy (or eBay) an excellent way of stopping dew and without the need of buying a control unit as well!!