Humidity vs Good Seeing

[Fordos Moon]

One of the apps I use has a default setting of Humidity being able to be 90% before seeing deteriorates. It is however adjustable.

What are your thoughts on maximum humidity before imaging could be noticeably affected? If it just means things will start attracting condensation then no problem with dew tapes?

[NGC 1502]

When judging sky conditions, I look at two things.

1.  What's the dimmest star I can see naked eye ?  From my town location, I know that on a good night I can just spot sub mag 4, after my eyes have adjusted for 5 - 10 mins, so such a nights is transparent and good for fainter objects.

2. How much are the stars 'twinkling' ?  It's rare from my location for them not to be, but if the twinkling is minimal, then the atmosphere is steady, good for planets & double stars.

You can have a night of good seeing, but high humidity.  If it's breezy, dew will be less of a problem, but seeing is likely to be less good.

On a humid night, whatever the severity, I'd pop the dew bands on, and start your imaging. You could use technology, or your own judgment.

Regards, Ed.

[Fordos Moon]

Ed, thanks for the reply and yes I agree technology is only so good but it comes in handy when not at home yet wondering if worth leaving early as conditions are good. I was just trying to establish if there was any reason other than condensation that humidity would significantly impact my imaging. I like the "twinkling" approach though - seems obvious now you mention it!

[Zakalwe]

It depends on what you are imaging. My best Jupiter and Lunar pictures were taken on nights when there has been mist in the air (enough for the moon to have a clear and distinct multi-coloured halo). The mist will lower the overall contrast (can be tweaked in post-processing) but the air was very very still. You won't get mist when there is much air movement.

i wouldn't dream of doing DSO imaging in those conditions though. For that you need good air transparency.