Foggy optics

[demographic]

I have a telescope (well its actually half a set of binoculars that got damaged) that must have slightly moist air inside it cos its alright when I use it on a sunny day but if I try and use it on a cold night it fogs up slightly on the inside.

Considering the fact that I sometimes use it for stargazing and looking at Jupiter and it's four moons I consider this to be a problem.

It's armoured and waterproof but has a little red screw with a seal on it that I can only figure is for sorting this problem out? Filling with nitrogen?

The little red screw looks like a bleed screw and isn't connectet to anything that it adjusts.

Anyway I figure the best way to get rid of the moist air inside it is to remove said screw, bung the whole thing in a tupperware container with a sachet of silica gel.

Anyone else got any ideas?

 

[brasst]

optics such as binos,telescopes, sights are indeed filled with nitrogen to stop the problem of fogging. your idea initially sounds feasable but i would be asking myself how / where the nitrogen escaped from and hence the moisture getting in.is the casing/tube damaged where it cant be seen?unless this is rectified you will continuously have the problem, if you did as you suggest have the bleed nipple open and in a warm dry environment somewhere that you can easily tighten it up in as if you change the environment while valve is still open the drop in air pressure even for just a short time will allow moist air back into the tube. see how long this solution lasts if its a month or two then it may be worth the hassle if not and funds permit buy a reasonable priced telescope as a profesional repair could cost you more

 

[bikething]

where abouts is this 'little red screw' ???

i once took apart a cheap pair of binoculars, and it had screws fitted for adjusting the prisms !!!! - about 20mm from the end of the prism housing IIRC.

 

[jayuk]

It wouldn't happen to be one half an ex-British army Avimo 7x42 black armoured binocular (the self focusing type) would it?

If it is, it definitely was originally nitrogen filled. Its posible that someone took them apart to clean internal mold/fungus/fogging and didn't have the facilities to refill them with nitrogen.

 

[demographic]

It wouldn't happen to be one half an ex-British army Avimo 7x42 black armoured binocular (the self focusing type) would it?

If it is, it definitely was originally nitrogen filled. Its posible that someone took them apart to clean internal mold/fungus/fogging and didn't have the facilities to refill them with nitrogen.

Not exactly sure but I got it from a squaddie mate who retrieved both halves after they had been thrown out onto a flat roof by the CO when he was in a pap over the place being messy.
It is indeed black armoured and self focussing (well I assumed it was at the infinity setting) and theres no facility for focussing either

The part that joins each half of the Binos had snapped and on the half that I got there was a part of the outer metal casing damaged, I repaired it with epoxy resin and now have a telescope .

My mate has the other half with the Graticule (sp?) in it with (from memory here) each space between graticules being 10 mills?

Does that sound right to you?

Edit, I have just put Avimo 7x42 into google and came up with this pic...

Which is exactly what I have half of

I suppose my next question is where do I take them to be re-charged with nitrogen?

 

[jayuk]

Hi, yes thats the ones I was talking about. I used to have a pair myself and was very happy with them, but eventually sold them when the rubber eyecups started to degrade.

I believe the German optical company Rollei also made a civilian silver colour bodied version for a short period. It may be possible to have them cleaned and refilled by them, but I fear the cost would be far higher than buying a used pair off ebay (the last excellent condition pair I saw went for about £80ish).

There are also some general binocular servicing/cleaning companies in the UK, but again I doubt it would be cost effective.

 

[Doc]

I wonder if it would be worthwhile leaving it in a warm dry place for a few weeks to try and dry it out a bit. Maybe with some silica gel sachets.

Just to be super-pedantic, Jupiter has rather more than four moons.....I was going to say 16 but a bit of googling suggests they've found 63 of them, so far. http://en.wikipedia.org/wiki/Jupiter's_natural_satellites

I've only seen four, anyway. It is well worth doing as you can see them change position over time, and you do not need high tech equipment, just ordinaty binoculars.

 

[demographic]

I wonder if it would be worthwhile leaving it in a warm dry place for a few weeks to try and dry it out a bit. Maybe with some silica gel sachets.

Just to be super-pedantic, Jupiter has rather more than four moons.....I was going to say 16 but a bit of googling suggests they've found 63 of them, so far. http://en.wikipedia.org/wiki/Jupiter's_natural_satellites

I've only seen four, anyway. It is well worth doing as you can see them change position over time, and you do not need high tech equipment, just ordinaty binoculars.

Aye yer right, but I can only see Io, Europa, Ganymede and Callisto with my half set of slowly fogging binos