[Stonius (Markus)]

After my recent experiences getting dewed out, I ended up making a dew heater from an Arduino that measured the secondary temperature and ambient temp and humidity, then calculates the dew-point and heats the mirror only a degree or two above that level.


I was very happy that it worked like a champ.


At about 2am I noted that the temperature had fallen to 4 degrees and the humidity had hit 100%, which concurred with the fact that everything else was sopping wet while the secondary was miraculously clear.


Unfortunately, my finder had long ago misted over, the replace ment red-dot finder had misted over in minutes, and even the 16" primary mirror was starting to go as well. Even the 'astronomical hairdryer' only gave brief reprieves, so I called it a night.



On the way home I was thinking what could be done. I could add another dew-heater for the finder. Maybe another for the filter rack and eyepiece, but what do people use for a large primary mirror? Do thy even make dew straps that big? Would it deform the mirror shape?



At that point I was thinking it was getting a bit ridiculous. Maybe there are just times you have to accept that dew has won the night.


How far do you go to combat dew, or is there just a point where you admit defeat? Do you factor the likelihood of heavy dew into your decision to go out?


markus