2ndary mirror dew removal?

[Tim]

Hmm, I have possibly just wasted a couple of hours thinking that the seeing was getting progressively worse, when in fact the 2ndary mirror on my newt was misting up. Good job for the wife's hair dryer.

Is there anything that can be done to prevent or lessen this? It hasnt happened before.

Thanks very much.

TJ

[GazOC]

One way is to run a wire across one of the vanes to secondary to power a dew prevention system.

[Tim]

actually heating the mirror with something?

I wouldnt want to make the vanesmuch wider, but perhaps one thin wire each for pos/neg along two vanes might work. I suppose then the opposite of a peltier would be required? Or is there something on the market?

Thanks. Still kicking myself for not thinking of that before wasting a couple of hours on it though :)

[GazOC]

http://stargazerslounge.com/index.php?topic=34424.0

[MikeP]

Hi Tim,

I bought one of these http://tinyurl.com/bxh2qx from Altair Astro for my FlexTube. It included some stick on copper thingy to use in place of wires along the vanes - I just used the wires.

It keeps the secondary clear and on one occasion when I was caught out, it cleared it fairly quickly.

You do need a controller for it though.

Mike

[Astro_Baby]

Do you have a dewshield for the scope ?

[acey]

Dewshield is the cheapest and best defence. Commerically made newtonians always have the spider too near the top of the tube to cut down on scope size. To remove dew a hair dryer works fine (12V if you're away from mains power) or try cupping an ungloved hand close to the secondary to warm it (though this freezes your hand). Aim your scope horizontally when not actually looknig through it - vertically aligned surfaces dew more slowly than horizontal ones (think where the dew forms on a car). Some people have advocated a shiny surface, eg silver paper, over the top of the secondary holder - I've never tried it.

Andrew

[Astronut]

A dewshield is very effective and relatively cheap and simple compared to heating methods. They also double as a lightshield too if you have to put up with any direct lighting in the vicinity.

[Tim]

I will check that link out in a sec, thanks Mike. The copper tape I have used before and is along the lines of something I was thinking of. I have 3 spare ports on my controller when using the GSO, as now I am off axis guiding I dont need another band on the guidescope.

Are dewshields really effective on a newt? I use a heated one on my SCT, and I heat the extending shield on the WO72 which works well. The reason I ask about the shield on the newts is that the 2ndary was 'upside down' the whole time, as it was towards the end of a 6 hour imaging stint on M81. So the 'dew' hasn't fallen on the mirror, rather formed as condensate on it as the night went on. I wouldn't be keen to alter the alignment during a session.

The other thing with a dewshiled is the extra weight on the front. With two cameras, focal reducer and extension tubes in the focusser the fore-weight is already problematic. Again, without glass at the front of the OTA, on the rare occasion when the neighbours lights come on, the important bits are fairly well tucked out of the light anyways.

Thanks for the tips. At least I know to check for that next time instead of just writing off the seeing as REALLY bad!

TJ

[Astronut]

I've never been out for more than 2 or 3 hours since I got my Astrozap shield from FLO but it kept the dew off the secondary for that period. The one I got was for a 12" SCT. It's a tight fit on the dob ie. the velcro only just fastens at the edge of the strip but it is secure. Not sure how heavy it is but I'm guessing around 1lb or less. I use a DIY counterweight for the dewshield, telrad and heavy eyepieces - a plastic milk bottle full of sand with magnets.

You say you've got extra power ports so one of those secondary heaters listed above might be of more interest to you.

[James]

Since starting to use a dewshield on my 10" Newt I've never had a dewed up secondary. The primary dewed up at Kelling last September though but surpisingly the secondary didn't :scratch:

James

[Tim]

hmm, I dont understand it, but i'll give it a go, maybe tonight if the clear spell materialises. Probably get the heater in the end though to be sure.

My aim is to have as fast and compact a unit as possible, with minimum setup/dismantle time, which is also capable of capturing nice images.

[timetraveller]

Hiya TJ

when i went to the Salisbury star party i was amazed and dis-heartend to discover just how quickly a newt will dew up so i bit the bullet and bought a dew shield from Steve and James and I'm so glad i did, not had a single problem since and weight is not a real factor at all bud they are not that heavy at all only had to make the very slightest of adjustments to my balance point hardly noticeable. regards Pete

[Tim]

Thanks Pete. Looks like it is time I put together yet another shopping list!

[psjshep]

Bit late to this party but....

At home, the dew is easily combated with a dew shield - that goes for the Newt & the 80mm refractor. Only on the most humid & coldest winter nights does the dew-shield get beaten.

At a star party like Kelling - that is a COMPLETELY different ball game. The best demonstration of this is the day after the night before - the queues @ the stands selling dew control equipment is awesome....

Phil.

[Tim]

Yeh, but that was a REALLY wet night! Funnily enough, my dewbands and dewshield kept all of my kit running clear that whole night, but I know many, including SteveL and others from here were beaten. Everything got a good soaking. In fact, it might even of been the wetness that killed my laptop power supply!

I've just had a look at the stalk of the secondary, and I think I am going to heat that, and add a dewshield to help keep the primary clearer.

As I will literally stay out the whole night if it is clear, then whatever system I go for has to be up to the job for quite some length of time.

Thanks for all the help