Best choice to deal with dew

[spaceboy]

Hi Everyone

I wanted to ask what members thought would be my best choice of dew prevention.

I have a 127 Mak which stands out to be the worst scope for dew but I hear secondary mirrors on reflectors can also fall foul to dew. My thinking is to go with a 12v Hairdryer which I can use on all 3 scopes when and if needed. I know dew tape or Shields would be the better choice but when you total up the cost of 3 different sized dew Shields and dew tape it comes to a small fortune. I understand I could just settle with a cheap camping mat but I read that dew Shields don't stop dew only delay it so I would need a hairdryer anyway.

Would just using a hairdryer be OK or would I spend most my night as a stylist rather than an astronomer??

Thanks for any advice

SPACEBOY

[Ags]

I just made a dew shield from an old neoprene exercise mat. I've yet to try it out with my Mak... I made it really long to exclude stray light and keep the dew away for a bit longer.

[spaceboy]

Hi Ags

How do plan to deal with the dew when it's formed though? The way I see it if you have to buy a hair dryer to remove the dew why not just use that all night as and when you need it?

SPACEBOY

[Ags]

I guess I'll find out... But I have noticed that dew often does not form under garden furniture or inside recesses - I'm hoping it will give me several hours of observing plus adequate cool-down time. Isn't that the irony - you need to let the scope cool down, and you know it's cooled when the dew starts to form!

[Astro_Baby]

Well I have a hairdryer as a fall back but the reality is once the dewshields fail it pretty much game over. AT SSP this year I had a 180 Mak and on the night the dew was bad I had to give up in the end. The dewshield alone couldnt stop it dewing and I didnt have a anti-dew heater band for the scope at the time.

The hairdryer could demist it but it pretty much meant running the hairdryer full blast all the time. By the time I got a few moments viewing in the scope was dewing again. In the end I gave up. By the way the Mak had reached ambient temp as it had been stored outside all night.

My own conclusions were that a dewshield alone would protect a Newtonian in all but the very worst whereas the Mak seemed to need a heated band and/or a dewshield or else its a complete non starter. A smaller Mak might fare better because the 180 is known for being a bit of a [removed word] in this respect.

[spaceboy]

So you spend all that money on a MAK just to get minimal viewing and they can't even supply a dew sheild as standard. Tut Tut.....

I only had the MAK because it was portable but if you can only get a couple hrs viewing what's the point in driving to dark skies? Wished I'd gone with a 150p

Astrobaby are you saying if I get a dew sheild for the 250 dob I should get a nights viewing from it?

[Steve 1962]

Hi there

I've made my own dew heaters using Nickel Chrome wire and heat shrink tubing from eBay. I've just put a fused cigarette lighter plug on the end of each heater and they work a treat - both at keeping the dew off and burning it off after it's condensed. I've not bothered with a controller - I just plug the heaters in and out as needed.

Here's a link to a set of instructions

Heaters

Here's some example links to Nichrome wire and Heat shrink.

28SWG Nichrome Resistance Wire (4M) Heating Element on eBay (end time 08-Dec-10 11:45:05 GMT)

1 Metre Black Heat Shrink Tubing 1.6 mm tube sleeving on eBay (end time 21-Dec-10 14:50:39 GMT)

If you can solder or use a crimper, you can make any number of heaters for very little cash.

Hope this helps

Steve

[Astro_Baby]

Well I have been out all night with my 200 and the dewshiekd keeps it dew free under all but the very worst conditions. SSP last year was abnormally bad on my last night but the mak 180 ( like most large sct / mak scopes ) seems particularly susceptible to dew.

My Nexstar 4 never had problems and could be relied to work with just a decent dew shield.

Persoanlly I believe desshields are the first line of defence, if it's dewing up after that with a closed tube design you need a dew band, beyond that a hairdryer for newts which may need just a quick bat on their secondary although I have found from experience once the secondary starts to go, assuming a dew shield is in ue, it's probably gone for good. The few times when the secondary on the newt has been hit by dew the primary has started dewing up just afterwards. You could fit a secondary and a primary anti dew heater but it all starts to get a bit mental really and when it's been that bad the eps have started to dew as well.

Given you need to cover a lot of different scopes I would either buy a dewshiekd for each or make one, get a hairdryer as well and see how it goes. If the mak still suffers you might need a dew Heater tape for it.

[ollypenrice]

I use relatively cheap dewheater strips directly from a 12 volt supply with no costly controller in the system. No issues at all. And no dew, ever.

Olly

[Revs]

I got myself an Astrozap shield, a Dew-Not heater strip and a car battery from a scrappers to power it (and the scope) and haven't had a problem since

[spaceboy]

Thanks all!

To be fair I haven't had any issues with the MAK as I had it in April so it's only really been out a handful of times during warm nights but I wanted to be prepared for winter. It sounds like I would be better off just using the reflectors & dewsheilds over winter .

Hi there

I've made my own dew heaters using Nickel Chrome wire and heat shrink tubing from eBay. I've just put a fused cigarette lighter plug on the end of each heater and they work a treat - both at keeping the dew off and burning it off after it's condensed. I've not bothered with a controller - I just plug the heaters in and out as needed.

Here's a link to a set of instructions

Heaters

Here's some example links to Nichrome wire and Heat shrink.

28SWG Nichrome Resistance Wire (4M) Heating Element on eBay (end time 08-Dec-10 11:45:05 GMT)

1 Metre Black Heat Shrink Tubing 1.6 mm tube sleeving on eBay (end time 21-Dec-10 14:50:39 GMT)

If you can solder or use a crimper, you can make any number of heaters for very little cash.

Hope this helps

Steve

I will look into this Steve as I assume the same principle can apply to dew heaters for eye pieces ??? as I read this can be a problem also.

Thanks

SPACEBOY

[Steve 1962]

I only really image - so any eyepieces are only ever out for a very short period of time and I've never had a problem.

The one down side of the Ni-chrome wire is that the less heat you want dissipated (i.e. the smaller the object you want to keep dew free), the longer the heater wire you need - a bit of a conundrum really.

Steve

[Moonshane]

it's funny Nick how we keep looking at the same problems at the same time

I have also made my own dew heaters (or have started anyway) using the resistor method. much like the nichrome method which I didn't like as it sounded like a lot of electronic calculations. there's a link to this method on the same page Steve has mentioned.

I have created a strand of resistors long enough for your scope (or maybe 4 x 2" EPs - i.e. two EP ones and two finder scope ones) and will be making more once I get the process nailed. I'll be adding pics when I sort out the system too.

it all works well off a 12v battery and via a dew controller (four channel) which I got used for £35.

in all I reckon I can make all the strips I'll ever need for <£20 so £50 and I'm sorted for two scopes.

I am also considering making a 'warm box' using a perimeter of the resistor chain so I can store EPs in that and they maintain their heat pending use. some people even say this is enough for EPs to prevent them fogging.

you could make a dew strip for your mak for <£10 and then you'd also have enough bits for a couple of smaller ones too.

[Moonshane]

oh, PS on the secondary (re newts anyway) I think a dew shield and keeping the focuser plugged should keep off the dew but see http://stargazerslounge.com/diy-astronomer/119754-smart-new-dew-removal-idea.html for a novel 'emergency' measure which worked for me.

[spaceboy]

Thanks Moonshane

I like the idea of that box for the EP's. I keep my old plossl in the obsy and although every thing is the same temperature the EP fogs up the moment I look through it. After 5 mins all is OK until I decide to look through another EP so this would help this problem. Well thats the plan as I don't fancy the alternative of holding ice cubes on my eyes until they cool to the temperature of the EP

I think I will leave the MAK in the loft until next year or sell it. Just sounds like too much fuss to me and I have my 200 I can always get a dew shield for. Would help with the contrast and work out cheaper.

How you getting on with the setting circles? Down to 3 weeks wait on the rotary scale so itching to go and get it. Have had some good simple and cheap ideas for fixing it to the base so should turn out to be a good mod.

SPACEBOY

[Moonshane]

hmmmm ice cubes on the eyes aaaagh!

if you cover my costs I could make a dew heater strip for your Mak, although you'd need to get a controller as the resistors get really quite hot at 12v. as I say about £10 would cover it. s'up to you - no pressure/worries either way mate.

I reckon I could make one in an hour from scratch once I get the process nailed.

not done much with the setting circles yet as people keep offering EPs and other goodies I want. I have bought a couple of used Orthos today!

I'll be getting some in the new year though and I'll be adding them to any truss dobs I make too.

[spaceboy]

Glad your getting offered EP's I wish someone would do the same to me. Can't believe I'm waiting on a 27pan and 13 nag to finish me set. Must have picked the most uncommon EP's. Gutted I missed out on the pan the other week but such is life

Thanks for the offer of a dew heater but whole dew thing seems to much hassle with the MAK. I don't really use it that often anyway so it would be pointless throwing money at it. ( hence seeing if a cheap hairdryer would be an easy fix) I'd put it on UK astronomy a while back as it wasn't getting much use so I may just drop it on the bay now and try and get a 13mm with the funds.

[Steve]

A dewshield delays the onset of dew, a heater tape with controller eliminates it. I would try the dewshield first. If you live at a low altitude and near a body of water you will almost certainly need a heater tape, but if you live higher up you might find the dewshield alone is sufficient.

After saying that, Maksutov's are notorious dew-magnets...

HTH

[Moonshane]

Glad your getting offered EP's I wish someone would do the same to me. Can't believe I'm waiting on a 27pan and 13 nag to finish me set. Must have picked the most uncommon EP's. Gutted I missed out on the pan the other week but such is life

Thanks for the offer of a dew heater but whole dew thing seems to much hassle with the MAK. I don't really use it that often anyway so it would be pointless throwing money at it. ( hence seeing if a cheap hairdryer would be an easy fix) I'd put it on UK astronomy a while back as it wasn't getting much use so I may just drop it on the bay now and try and get a 13mm with the funds.

the problem is that people tend to hand onto the best EPs

have patience. they'll come up eventually. usually after you've given up and spent up on something else.

on the warm box, some people use those re-usable hand warmers which are ten a penny. might be worth a shot as an easy fix?

[spaceboy]

Good thinking moonshane I saw these (heart shaped) hand warmers in Lidl for a £1 but didn't think they would last the 1/2 hr journey to my dark site but if I was to drop them in my eyepiece case they may be insulated. I admit I did have an issue with the whole heart shaped thing but I do love my TV's

SPACEBOY

[dlp]

I only really image - so any eyepieces are only ever out for a very short period of time and I've never had a problem.

The one down side of the Ni-chrome wire is that the less heat you want dissipated (i.e. the smaller the object you want to keep dew free), the longer the heater wire you need - a bit of a conundrum really.

Steve

You can get NiChrome wire in different gauges though, and/or reduce the voltage.

[Moonshane]

Good thinking moonshane I saw these (heart shaped) hand warmers in Lidl for a £1 but didn't think they would last the 1/2 hr journey to my dark site but if I was to drop them in my eyepiece case they may be insulated. I admit I did have an issue with the whole heart shaped thing but I do love my TV's

SPACEBOY

no worries mate! the simple solutions are often the best. if you bought a few, you could 'click them' in succession and keep it warm.

[Ags]

First light (or is that "first dew") for my dewshield. The dew was heavy tonight - my finder was misted after 20 minutes, the scope hadn't even cooled down. I had guests so could not look at Jupiter until 3 hours later, so I was pleasantly surprised to find my corrector plate was still dew-free!

[Steve 1962]

dlp's correct about thinner gauge wire and lowering the volts - just for clarity, I was refering to my situation with a roll of fixed gauge wire and a 12v supply.

I like the idea of those handwarmers

Steve

[dlp]

Made a dew shield for my Telrad at the weekend - tried it out tonight, and it's the first time it hasn't dewed up within 5 minutes of going out. Well chuffed for just a few minutes cutting up a piece of foam sheet and attaching a couple of velcro dots (both from Hobbycraft). I got the design from Home Built Astronomy Projects - Rod Nabholz