Time to invest in some dew heaters?

[matsey]

I *think* my scope is starting to suffer from the dreaded dew.... though having only been observing for a few months and never having experienced dew problems before, I'd first appreciate confirmation what I've been experiencing is indeed caused by dew...

I had my first early morning session yesterday (3.30am onwards), and a short session yesterday evening (7.30pm onwards). Used a dew shield both times. After approximately a couple of hours in the morning, and only an hour in the evening, I started to notice a weird effect in the eyepiece. The best way to describe it was that the outside 50% of the view through the eyepiece was clear and dark, but in the central area the sky looked a mid-light grey colour, and the view in that area wasn't quite clear.

Does that sound like dew build up? Or something else? I'm pretty sure the problem was with the eyepieces rather than the scope itself - when I was using my binoviewers the effect was much more noticeable in one eyepiece than the other, and some eyepieces seemed worse than others.

When thinking about dew heaters I was originally thinking I'd only need one for the scope itself... so do I need to get one for the eyepiece/diagonal as well? The red dot finder became pretty useless as well, I suspect for the same reason.. worth getting one for that, or as it's just clear glass, can I just wipe it dry?

And, finally...! ... up until now I've also been storing the eyepieces in the accessory tray under the scope with the caps off... would it be advisable to keep the caps on in the tray to prevent dew forming when not in use?

Thanks as always for all advice and answers to my newbie questions.

Matsey

[The Bat]

It's easy to check if you have dew forming on your scope: shine a light onto the front .

If it's on the eyepiece, sometimes that happens if you breathe on it accidentally as you approach the eyepiece. But if you are leaving them uncovered, they may well be suffering a bit of dewing. Tips would be to keep eyepieces covered up any time you are not using them to observe - so yes, cap the top if you are storing them upright in the accessory tray. Also, if you keep them indoors until you are ready to go out and observe, they will be warmer than outside and will stave off the dew that bit longer. An easy fix I use if they get a little misty is to put them indoors for a few minutes just to clear the mist (I've even done that with the scope before now). You can also try using a hairdryer to de-mist but try not to point it directly at the optics; give it a gentle waft from the side.

As for the main scope, it will mist up more quickly if you are looking at objects overhead, so I just try not to look at the zenith too much until later on in a session so as not to attract too much dew too early.

I thought about dew heaters early on when I got my scope, but in 3.5 years I haven't had enough problems to warrant the expense, but I am rarely out for more than 2-3 hours at a time. If you are doing extended observations and/or imaging, then it might be worth the investment.

Rachel

[matsey]

Thanks Rachel, appreciate the response

I did try shining the light into the scope but couldn't really see anything untoward, so I do think it was just with the eyepieces. But from what you've said though, it does sound like dew. So definitely from now I'll get into the habit of leaving the caps on when in the accessory tray... and I'll try not to breathe on them too !!

I'll see how that goes for now, but given the Saturday evening's viewing was disrupted for me after only an hour, if this does start becoming a regular problem I'm pretty sure I'll end up getting some dew strips anyway... I guess if I can stop the misting up in the first place, I won't have to go to the trouble of stopping and rectifying the problem every half hour or so throughout the session.

Thanks again

Matsey