Hi Chris,
Yes it's a common problem but there are cheap solutions. I have no doubt I'll be scorned for suggesting what I've used but I recently was out in the feild and it was -2c and everything dewed up and froze, even parts that are connected to me and yet I didn't get one bit of dew on my lense. So here we go.....
Go to a craft store and pick up a black sheet and that looks like thick card board but is actually a plastic material that is flexible. Make a tube about will go over the end of your OTA and extends past by a couple of hundred mm.
The bit I'll be scored for....... I bought an outdoor dog vest at the reject shop for $20 and wrapped it around the OTA...... Not one bit of dew since...
Or splash out and get a dew heater .....
Hope this helps
