Predicting dew

[domstar]

Hi everyone,

My last couple of times observing have left my scope sopping wet with dew after a couple of hours. The objective is ok but lens caps, finder and main tube get all wet. I haven't really had a problem before. My question is, are there certain conditions that produce more dew? Is a sunny summer's day worse than a coolish day in autumn? Is there anything i can do, for example set up later? And given that I have to pack up in order to go home, is it ok just to leave my case open until morning with the lens caps off (the amount of dust in my house is not to be sneezed at)? Any advice would be welcome - the onset of dew worries me when I am observing and I start to think about packing up. Should I just ignore it?

[MARS1960]

I wouldn't worry, if observing you can just wipe it down if you want.

I generally image so use a dew heater to keep the lenses clear, but if observing you can just wipe those with a nice clean microfibre cloth.

I always leave my gear out with caps off when i bring it back inside.

As for predicting it, mmmmm, unfortunately dew is more likely on clear nights with highish humidity, especially after a hot day.

[N3ptune]

I notice during summer after a few days of rain, really high temperature during the day, ambient hot air packed with humidity and a drop of temperature at night, dew will deposit on the gear. Hot air can retain more humidity then colder air.

I just look at the humidity forecast for the night, at around 70% and more, I know there will be dew to deal with. I keep my eyepieces inside a box with a cover during the observation.

You can read about the dew point too.

http://www.calculator.net/dew-point-calculator.html

And this the psychrometric chart, I don't fully understand how to use it but I know it has the answers to many question regarding air, humidity, temperature, pressure etc.

http://www.coolerado.com/pdfs/Psychrmtrcs/0000Psych11x17US_SI.pdf

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In the house, I let the telescope and eyepieces dry in a dry room, remove the caps and put a tissue over the opening it to prevent dust from getting in and a tissue over my EPs box. Next morning I put the caps back on, close the bag and EPs box with silica gel inside.

Never had any problems so far.. if this can help.

 

[RichM63]

Yeh Dom, leave your gear open to the elements when you get home, it is the best way to naturally dry gear.

[Joeistotalycool]

I would download flo's clear tonight app. It gives you all the details