Dew Heaters

[malc-c]

My 200P often dews up, and whilst I've used home brew shields, I still find that the secondary still dew's after some time.

Is it possible to use dew heaters on a newt, and if so do they produce any thermals in or around the tube ? - As Mr Spock said in another thread, seems strange to spend ages cooling a scope down only to heat it up again !

[barkis]

Have a google about humidity and dew point, It's an interesting read, and will explain about air containing water, and why it will at times deposit it all over your mount, scope, and laptop if your outside, basically, if you keep your optics at a temperature slightly above the dew point, you can keep dew from forming on their surface. I don't know if you wear spectacles, but if you do, and you have been outside on a very cold night, and you go indoors to your warm cosy home, your specs will mist up when you enter the warm, to get rid of the misty deposit, which is in effect water, you need to warm them up to clear them.

Bit of a long winded, and obscure description, but Wiki or other info service will explain it better.

Ron.

[hayju01]

As Mr Spock said in another thread, seems strange to spend ages cooling a scope down only to heat it up again !

I'm no scientist but the reason we cool the scope is to get everything to the ambient outside temp and reduce the air flow caused by the whole thing cooling whilw trying to use, plus contraction of all things as they cool. The reason we heat the 'glass' is because it cools at a faster rate to eveything else and therefore will be colder than everything else including the ambient air temp once this temp hits the dew point bam you're 'dewed' and it is time to pack up and go home. In theory the dew heater will keep the 'glass' closer to the same temp (they never get that hot in fact barely warm) as the rest of the scope thus minising thermals and (help) preventing dew depending on the dew point on the night. I would always recommned using a dew shield in conjunction with a dew heater as dew starts by forming downwards e.g. onto upward facing side of objects with a shield this is the first few inches of the shield itself not the 'glass'.

I have removed by shield at the end of sessions and it has been quite wet and yet not a jot of dew on the 'glass'.

just my theory and has worked well so far for me. (apart from when i dont practise what i preach http://stargazerslounge.com/beginners-help-advice/162800-learn-my-mistake.html )