Reply To: Suck or blow

Forums Telescopes Suck or blow Reply To: Suck or blow

Grant Privett

I think I prefer a short duration dewing as that gives less time for the water droplets to absorb gases from the atmosphere and become acidic. Though, with the reduction in heavy industry over the last 50 years and diminished use of coal powered fire stations, perhaps I am being over cautious. But, realuminising mirrors ain’t cheap.

I was also disappointed that parking the telescope horizontally didn’t encourage the droplets to run off better – most of them seem to stay attached to the mirror. I assume its a surface tension effect.

Yes, I take your point regarding air temperature, but think the combination of glass being a poor thermal conductor and a fan means the surface of the mirror (not the bulk) can follow the air temperature quite closely. Thats very handwavium, but I don’t have time to make a mathematical simulation. Anyone?

I can remember many still nights with dew, but not that many windy ones – though it may be a selection effect as, before the dome, I didn’t observe on windy nights for fear of tube vibration.

I also considered a dehumidifier, but need to check the energy consumption first – a dome isn’t exactly a sealed system. A small computer fan is very low power, hence my enthusiasm.

I think the main change I need to apply now is a very fine mesh net over the secondary end of the tube to try to catch the bigger debris and discourage spiders.

Just checked. Third morning in a row without any condensation, ice or droplets on the mirror and none present when I used the telescope on the 27th. Will keep checking every morning.