16" lightbridge primary dewing up

[scarp15]

Yeah Silica gel might possibly help. I purchased some recently off ebay to take to Kielder, more so to place in my eyepiece case though, after hopefully, a good but likely damp session.

Now you've made the leap, I guess there's no going back, although probably would be great to have been able to keep the 12" as well for options.

[crashtestdummy]

I could have easily kept the 12" tbh I only got rid because I find it hard to choose with many option

[nicks90]

you're not having it back Crash!!!!!!!! its mine, I tell yer, all mine!!!! mwuahahahaha

[crashtestdummy]

The 16" does pack down smaller than the 12" but the 12" didn't need much in the way of mods

[scarp15]

I am curious to see how the rumoured 18" / 20" truss skywatchers are presented. I will be considering 16" - 18" in the next year or two. These large mirrors (damp UK climate) may require new solutions to dew prevention. Someone should come up with an idea for optical friendly 'windscreen wipers'.

[nicks90]

maybe someone can be brave on an old mirror and apply some Fog-X anti fogging spray and see if it a) ruins the coatings ruins reflectivity and clarity.

certainly doesnt appear to make any difference when i apply it to my glasses - other than stopping them fogging up.

[crashtestdummy]

I avoid using that stuff on my windscreen so it's going knowhere near £1000 mirror

I think the secondary fan idea blowing across the mirror would help.

Thinking back,it wasn't seeing from the edges as nor so it was more middle outwards so likely dew going down the tube from observing at zenith

[Moonshane]

to me this possibly indicates that the fan was over-cooling the mirror assuming it's centrally mounted. is it a standard fan or one you have fitted yourself? maybe try running it at 6v rather than 12v so it effectively runs at half speed. if the batteries ran out quickly then maybe it's drawing a lot of power and blowing really quite cold air on the mirror? you really don't need a large fan on even a large mirror an 80mm fan is more than adequate

if the fan cools the mirror to a point far enough below ambient, then it will dew up if the conditions are damp.

personally I'd try it without the fan.

[Moonshane]

this is interesting to read http://www.skyandtelescope.com/howto/visualobserving/3304226.html?c=y&showAll=y

it sort of contradicts what I just said though.

[Bart]

this is interesting to read http://www.skyandtelescope.com/howto/visualobserving/3304226.html?c=y&showAll=y

it sort of contradicts what I just said though.

As you say, I found the fan possibly causing the problem some nights, contrary to what I might have expected.

Barry

[crashtestdummy]

Yes standard fan in standard central position.