50mm Guidescope Dew Prevention Options

[bendiddley]

So I have two options in front of me at the moment for sorting the potential dew issue on my 50mm guidescope, to go for a dew heater tape or a dew shield. Would prefer the latter as it's a lot cheaper, but wondering if the dew heater route is better, any thoughts please!

[Commanderfish]

Really for a scope the best thing is to have a dew shield with heater tape built in, less faff, max protection.  THAT SAID, for a little 50mm finder, I reckon you could knock up a home made dew shield of a fairly long length with a piece of camping mat or similar material.  Should cost peanuts.  

Another idea is to find yourself a transparent plastic lens cap to fit on to finder at the objective end.  If it's transparent enough (like the ones on the Baader sky surfer V RDF) you could actually use the finder with the cap in place.  If not, just whip the cap off when you actually use the finder and keep it in place the rest of the time.  As 50mm is a very common size (about 2" external diameter) you've got a fair chance of finding something transparent which is suitable to fit.

With my Baader Sky Surfer I pretty much always have the transparent dew cap on, I forget it's there. A big plus with this approach is that if the cap dews up you could just wipe it off (as it's not real optics, there's not much stress about scratching them), or just take it off.  It will have protected your finder from dew for x hours and then you've got y hours more with the cap off before the objective lens itself dews up.

[iPeace]

Having tried dew heater tapes, there is no way back for me...they're just so effective.

Hope you can get a nice cheap solution to work for you.

[Ben the Ignorant]

A friend buys cereal boxes regularly because he has two kids; that gives him plenty of disposable carton to make dewshields for his refractors (astrographs), printed side outside, bare side inside. They look ugly and kind of fancy, too, with their childish colorful deco but what matters is carton absorbs water in the air, that's more effective than keeping moist air close to the optics, and warming it.

After the night he dumps the carton, costs him nothing.

[bendiddley]

Cheers commanderfish but the finder scope is actually a guidescope for my imaging set-up so a transparent cap isn't going to work, but thanks anyway. peace, thanks any recommendations? Ben the ignorant, like the concept but not sure I can be bothered with the faff or making them on a regular basis.

[Commanderfish]

Well for what it's worth, I have just bought some 3mm foam from here, as recommended on another thread in this forum.  I'm going to use it to make a dew shield for my 16" dob.  As 50mm is not a standard size for dewshields I reckon this would be your best way forward for a dewshield:
https://www.easyfoam.co.uk/closed-cell-polyethylene-foam.php

Or if power is not going to be an issue you could go with just a 2" eyepiece heater tape from 365 astronomy. You need about 17 cm for a 50mm guide scope and these are 20 cm long.  I have one and it works a treat for EPs.  I like using it on my eyepiece as when you put your eye to the eyepiece your face gets a nice warm  soft welcome

http://www.365astronomy.com/Dew-Heater-Strip-for-2-Eyepieces-20cm-Long.html

[Ricochet]

I made a dew shield for my 9x50 RACI from a section of thick cardboard tube that are commonly used for protecting posters and the like from heavy handed couriers (in fact it might even have been what FLO sent my Cheshire in). I cut a section out of the tube to make it the right diameter to hold on by friction, flocked the inside and finished off the outside with some normal sticky back plastic that I happened to have. As far as I can remember it has never dewed up but as a visual astronomer the scope only stays out as long as I do so you might find you need power for a guide scope that is left out all night.

[nightfisher]

I have made dew shields for 50mm finders, i use a smoothsided plastic drink bottle (perfectly clear drink) and black flocking for the inside, works a treat

[bendiddley]

Cheers guys, so how long do you find your shields keep the dew away on your 50mm finders?

[Ricochet]

It's difficult to say as my memory is terrible but given that I haven't stayed out all night with it  I would guess that the longest I've left it uncapped is going to be in the region of 5 hours. It's worth remembering that what you're trying to do is to cut down the angle of sky that the objective can radiate heat to so the longer the shield the longer the time before the objective dews up.

[nightfisher]

I find my home made shield which projects about 50mm out from the lens keeps the dew at bay very well and cuts stray light reflection as well, i will have a browse and see if i can find a pic, i may well have done a thread in DIY section

 

[bendiddley]

Thanks night fisher I like the drinks bottle idea, I might give that a go.