Dew on my finder scope.

[johnkirkpatrick]

I was out last night and after leaving my scope to cool for an hour I went out and got 10mins viewing before my 10x50 straight through finder had dew on it and was completely useless. I have some old camping mat, Will that rid the dew and if so what size do I cut it to and how do I fix it to my finder, And will it affect the finders FOV??

[perrin6]

It probably helps to leave the scope in a horizontal position when you ar'n't using it to minimize dew on the finder objective. When it does dew up I just wipe it with a paper towel or a handkerchief ! It's home made using bino lenses so I suppose I treat it with less respect than if I'd paid a lot of money for it,

Alan

[Chris H]

Best to keep the caps on the finder scope until you need to use it. A dew shield will work up to a point, once the finder cools to the dew point its going to mist up no matter what. I use a Telrad and remove it from my scope whilst the dob is cooling it still get dewed up pretty quickly but short of using heater strips there's little that can be done.

[Bizibilder]

Kris beat me to it - but I keep the caps on the finder except when actually looking through it - seems to work. (The cap gets covered in dew instead!).

[perrin6]

Here's an idea; What we need is something akin to a skylight or UV filter like photographers use on all their lenses. This way you can wipe it to you're hearts content and when too scratched just get a replacement - much cheaper than buying a new finderscope,

Alan

[Moonshane]

Here's an idea; What we need is something akin to a skylight or UV filter like photographers use on all their lenses. This way you can wipe it to you're hearts content and when too scratched just get a replacement - much cheaper than buying a new finderscope,

Alan

that's a good call Alan

there's lots of them on Astroboot usually. you could hold it fast with a little silicone sealant or even black insulation tape.

[JamesM]

To be honest I like to keep things simple so I too agree with Kris77 and Bizibilder with putting the caps back on when you're not looking through the finder.

James

[Astro_Baby]

I tend not to use the finder much after I have aligned. Keep the caps on is a good way of dealing with it. I suppose you could alway get extreme and put a dewband on it.

I found when I tested a whole load of finders that most had dewshield that were too short. An extra bit of dewhield wont do any harm.

[Skills]

I fitted a dew shield to my finder: approximately 9inches, so a bit overkill, made from a camping mat. It doesn't affect the fov and now my objective lens is dew free however the eyepiece dews up frequently even if I keep replacing the cap between viewing. I warm it a bit by wrapping my fingers around which helps but the dew is a bit of a pain...

[perrin6]

Shane - I've just dug through my old photography bits box & found a UV filter & a skylight - but both are 50mm & I have a 30mm finder - looks like I've got some filing down to do - hee hee. (Took me a long time to realise it was pointless filing all the corners of a 50p piece so I could pass it off as a 10p coin)

Also found one of those absorbent small camping face-towels which I'll use on the finder objective / filed-down filter thingy (but not the diagonal I hasten to add)

Alan

[perrin6]

ooh ooh.......Dob mod idea - a handy-dandy hook for hanging the camping towel/finder objective drier on!

Alan

[perrin6]

I fitted a dew shield to my finder: approximately 9inches, so a bit overkill, made from a camping mat. It doesn't affect the fov and now my objective lens is dew free

Sounds like a better idea - avoids having to wipe it at all,

Alan

[Perryellis]

Some really good, simple ideas here. Keeping the caps on the finder while not in use and keeping the telrad/finder inside while the scope cools. Obvious...Why did I never think of that!?

I do plan to make a dew shield for my telrad and scope soon. I found this guide recently Home Built Astronomy - Telrad Dew Shield

[Moonshane]

this is a great Telrad shield. I got one purpose made from Astroboot for £3. that said it still occasionally gets dewed in really bad conditions although better when yo don't leave the scope pointing at the sky.

[WayneR]

More great advice guys, thanks from another interested reader.

[Astro_Baby]

A thought on this - its not the solution for everyone but one of the nify things with the Baader Skysurfer V is that its endcaps are actually transparent - neat eh - you can leave the end caps on and if they dew you can just wipe them with your glove safe in the knowledge your not touching its optical surfaces.

NOw whats needed is someone to make something similar for a conventional finder.

[delsix]

Would it be possible to coat the surfaces with something like this Super hydrophobic surface using nano-technology :: Amazing