[Laser] Re: Atmospheric effects on optical DX, 50 miles

[Tim Toast]

probably the best way to avoid dew is using a dew cap
and a heater for the lens or mirror. 
here's some info about dew:
http://www.astro-tom.com/tips_and_advice/dewing.htm
Since you're using a cover glass, you could heat that
with a heater wire. 

If you can insulate the box really well, the heat from
the driver might warm the inside of the box and lenses
enough to keep them from dewing (assuming the driver
is in the box). If that's enough maybe you can get by
without a large dew cap.
If you cool the photodiode down with a peltier then
you're going to have dew problems there as well. Not
sure how to deal with that really other than using a
vacuum sealed thermos bottle type container with a
heated window

> 
> Also, a major problem with our optical DX has been
> the loss of lens 'gain' 
> through dewing late at night. It always pays to keep
> the lens or its cover 
> glass a fraction of a degree in temperature above
> ambient to avoid 
> condensation. As I use a series class-A modulator on
> my 1-watt Luxeons, we 
> dissipate quite a bit of power as heat from the
> series modulating transistor 
> (type MJ15003) and the related current limiting
> resistor. Surely there must 
> be some way of channeling this heat energy over the
> lens, perhaps with a 
> small muffin fan, to reduce the tendancy to the
> formation of dew?
> 


Tim Toast
http://www.aladal.net/toast/

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