I'm sure that if you take notes at the eyepiece, or sketch at the eyepiece too, dew can be a real pain in the neck,
Stay out long enough in dewie conditions, and your pages achieve the consistency of wet toilet paper,
I've recently made a dew hutch for my gear following the article by Scott Tannehill for a dew hutch
. This led me to consider using some of these ideas for my sketching purposes.
It isn't enough just to whack together bits and pieces. I considered the angle of the incident light causing unwanted reflection off the paper. I also considered that the light source needs to be able to be moved about easily to position it where I'm working on the page, and still cover the reflection issues.
The pictures below show what I've come up with. I used some of the left over black coreflute I have, and picked up some thin perspex off-cuts from Reverse Garbage. As I'm right handed, the coreflute is bent around the left corner of the perspex, and the top section of the coreflute over extends the perspex a small amount. The coreflute is fixed onto the perspex with waterproof tape.
A little mellamine off-cut, a couple of bolts and wing-nuts became the clamp.
The red light head lamp I normally use is readapted onto this rig, attached with a strong clip. The lamp has a moveable head, and the whole thing can be attached to the top left corner of the coreflute, or repositioned along the left, down reaching section of the coreflute. This also gives me the best control of the reflection off the page.
The thing to note is that you need to hold this rig fairly upright. That is the only way you'll be able to combat the dew falling onto the page. I'm quite happy with this method of working as I've had to adopt it anyway to maximise my 'dew time'. This rig won't necessarily totally stop dew, but it should give you considerably more time to work on the paper before dew starts to become an issue.
I hope this gives you some ideas on making your own writing/sketching dew hutch.