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Hi, I've got a Celestron XLT Omni SCT

the last couple of sessions have been ruined by dew.  I've got an astrozap heated dew shield on the way, but I read somewhere about insulating Maks/SCTs.  Has anyone got any tips on what material to use and the best way to do it?

thanks

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2 hours ago, W0nderste said:

Hi, I've got a Celestron XLT Omni SCT

the last couple of sessions have been ruined by dew.  I've got an astrozap heated dew shield on the way, but I read somewhere about insulating Maks/SCTs.  Has anyone got any tips on what material to use and the best way to do it?

thanks

I've read of this being used...

https://www.amazon.co.uk/SuperFOIL-General-Purpose-Insulation-Wrap/dp/B075XKJ9LQ/ref=psdc_1938186031_t1_B07NS6BB89

I made a dew-shield from the stuff for a relation's C90 Maksutov...

1094004925_dewshield3.jpg.d690c477311a6b6ee8eacea2858fa391.jpg

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That foil-effect sheet looks just like the car windscreen frost protectors, very cheaply bought from various places.

Quite frankly I've never had an evening where my 8SE front corrector plate dewed up completely before it became impossible to see through the eyepiece, that's with AstroZap heater tapes on both and a dew shield.  If the dew gets that bad then it's probably time to call it a night as your breath or the heat from your face will likely fog up the eyepiece before you get a chance to look through it properly.  Unless you can also protect your finder, that will likely be the first to go (I have a tape on mine, need to make a mini dew shield for it soon; the red dot finder is probably a lost cause though).

I flocked the inside of my tube to improve the contrast but thinking about it now it could actually help with dew as well, if insulation helps.  Thing is though that dew occurs mainly on the outside surfaces, that's what I thought the main heater tape and dew shield were there to protect.

I recommend a 4-channel dew heater controller, I use the HitechAstro one which includes two 12v power sockets as well, means I only need one plug going to the battery.  Don't ask me what power settings are best as I'm still trying to work that out myself, I usually just stick them in the middle and hope for the best!  I've heard that too much heat creates thermals which ruins the view.

 

Edited by jonathan
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Thanks everyone.

luckily my astrozap heated dew shield arrived today.  It came with EP heater and HitecAstro controller, so I will fit that and try the insulated Foil sheet as well.  
i was just very keen to make the most of Mars opposition this month but the last two clear nights were somewhat spoiled by dew problems

for those running tge HitechAstro controller, what are you using to power it?

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Just for clarification, insulating scopes is done to reduce thermal currents and improve the quality of the image. It's an alternative to having a longer 'cool down' time, which can be significant for Maksutov scopes. 

Insulating may have a minor effect on dewing, but only because it'll keep the corrector plate slightly warmer for longer, but the benefit will be minimal. A dew band will be far more effective. 

Edited by Gfamily
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20 hours ago, W0nderste said:

for those running tge HitechAstro controller, what are you using to power it?

I plug mine directly into a 12v leisure battery (not exactly the same one as this, but Yuasa are a reputable brand) using a pre-made short adaptor cable, available from any auto spares shop such as Motosave.  I sometimes use a smaller Yuasa 12v battery but it uses spade connectors so I had to make my own adaptor cable for that, same kind of thing though.  A large leisure battery with normal car battery style terminals will be easier to connect a charger to, I used a Ring Smart Charger, maybe a bit over the top but I like the refresh and battery recondition functions it has, and it's built like a tank.  Best to make sure the charger supports the type of battery you buy (there are different chemistries and construction types).

Edited by jonathan
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On 12/10/2020 at 00:33, W0nderste said:

Hi, I've got a Celestron XLT Omni SCT

the last couple of sessions have been ruined by dew.  I've got an astrozap heated dew shield on the way, but I read somewhere about insulating Maks/SCTs.  Has anyone got any tips on what material to use and the best way to do it?

thanks

Oh! A dew shield AND insulation?

Hmm!  Not got  dew shield yet.  Might have to wait for the next credit card cycle :o

But something like this looks like what others are using as insulation.

I'm confused tho.  It's early in my checks so I haven't look at the SGL DIY section yet, but how/where are we putting the radiator backing? 

Is it important to get self adhesive stuff or actually worse?

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5 hours ago, kevenh said:

I'm confused tho.  It's early in my checks so I haven't look at the SGL DIY section yet, but how/where are we putting the radiator backing? 

 

Is it important to get self adhesive stuff or actually worse?

Some knicker elastic tied around it should probably do the trick!  No joke, just buy some from haberdashery, add a clip or whatever, away you go.

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10 minutes ago, jonathan said:

Some knicker elastic tied around it should probably do the trick!  No joke, just buy some from haberdashery, add a clip or whatever, away you go.

Think I’ll order from eBay to save my haberdashery blushes 😬
Not that I’d know where to find a haberdashery anyway 🙂

 

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Please take note, I am only a visual observer.  I do not do any imaging.  I know nothing about imaging or the technical difficulties with imaging.

I have a Celestron Nexstar 11 that I have purchased in 2003. (I also have a few other telescopes,  but I mostly use the Nexstar 11)

So I have been using it for 17 years here near Chicago USA.   As far has fighting the battle with dew and possibly frost, I mostly use a heat gun/hair dryer in combination with a dew heater band.  I have also have  a dew shield, but they seem to be cumbersome.

Now let it be understood: I have read in the book the Backyard Astronomer's Guide by Terence Dickinson and Alan Dyer  that dew and frost could be slightly acidic like the famous acid rain dew will eat away at the coatings on the optics of such things as a corrector plate of SCT.  A SCT has a very large piece of glass just asking for dew to accumulate. They called it  a vampire that will suck the life blood out of your optics. So just the mere act of dew accumulating on your optics should be avoided. But dew and frost have been getting on my corrector plate for a long time and I am still using the same telescope.

I did have a dew strip heater that I bought from Orion telescopes that was very thin and I could use both a dew heater and the dew shield at the same time.  But my new dew heater is too thick to use a dew shield with it.  I suppose could work something out if I tried hard enough.   Wonderste mentions heated dew shields.  I have not heard of that before. I do have an Astrozap dew shield but it is not heated.

I will use various techniques simultaneously. But for sure I always have a heat gun ready for use. Probably a hair dryer would be better, you must be very careful when using a heat gun.

If you use a heat gun or hair dryer, apply the heat from a distance and only long enough to clear the dew.

I have often used only a heat gun for dew removal. It works. But the problem is that the heat from the heat gun will effect seeing for a little while. Then shortly after the seeing returns to normal, the dew will build back up.  This technique works.  I have been using this technique for years because for me it is the most basic technique that does not require any special equipment.  The old KISS principle (Keep It Simple Stupid.)

With a dew shield in place I could not reach in with the heat gun to effectively remove and built up dew or frost.

Once the corrector plate (the large glass lens in the front of a SCT) comes to ambient air temperature   dew and frost   will accumulate rapidly once you remove the lens cover.  

A heated dew band seems to work well.  It depends how cold it is outside, the humidity level  and how big your corrector plate is.  Sometimes the heated band will not keep dew and frost off of the entire corrector plate near the center where the secondary mirror is located.  The heated dew band will definitely keep the outer portion of the corrector plate clear.  When dew or frost builds up towards the center of the corrector plate, I will use a heat gun just enough to clear the dew.  This will effect  seeing for a little bit. 

A  heat gun is also handy for removing condensation on the lenses of the eyepieces.

Discussion on dew heater strip:  You could make a dew heater strip see this web page:  http://www.deepskywatch.com/Articles/newtonian-dew-heater.html

 

I didn't make the one I have, I bought, a DEW NOT brand. But any cheap one will work. I paid about $40.00 for the one I have.  I do not use those expensive controllers, to me they are a useless rip off.  You could spend hundreds of dollars on heated dew  bands and controllers.  The controllers  adjusts the amount of current through the dew band, thus control the amount of heat. But I need to have my dew band produce maximum heat. Even then the dew band doesn't get hot because it is transfers the heat to the corrector plate and aluminum frame. Even with maximum current  the entire corrector plate does not remain free of dew.  Just connect directly to a 12 VDC source.  I use a car battery to run my Nexstar 11 electronics and the dew heater, but  you could use a deep cycle marine battery or a good ac to 12 VDC power supply.  But you need about 1 amp or so, most 12VDC plug in power supplies do not have enough current to run a dew heater strip.  There are also dew heater strips available for eyepieces, I have never used one.

 

 

 

 

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5 hours ago, hoss said:

I didn't make the one I have, I bought, a DEW NOT brand. But any cheap one will work. I paid about $40.00 for the one I have.  I do not use those expensive controllers, to me they are a useless rip off.  You could spend hundreds of dollars on heated dew  bands and controllers.  The controllers  adjusts the amount of current through the dew band, thus control the amount of heat.

As you have a large tube then maximum heat may be what you need, but for smaller OTAs this might be too much and result in unwanted thermals emanating from the front of the telescope.  I've sometimes experimented with the settings on my dew heater controller, on minimum power the dew will form on the corrector plate almost as normal, assuming it is a dew-prone night, with the power set at 50% the dew will start to receed from the outside within seconds; the balance point will be where the dew receeds and only just does not form again, too much power and it's a risk of those thermals, at the very least a waste of amps.  The ideal setting will result in a temperature just above the dew point, something which is variable from one night to the next.

A dew controller can also provide additional power points, mine has two aux ports (12v), one of which I use to power the mount.  My controller allows individual power levels for each of the four dew heater tape outputs, so for the smaller tapes around finders and eyepieces I might not need as much power as the main OTA heater tape.  If I didn't use a controller I'd want to find a typical heat requirement for each tape (eyepiece, finder, etc) and design my electronics appropriately, buying the controller saves me a lot of time, effort, and it comes in a neat pre-made package which is better than anything I could end up building. 

At the end of the day we all use what works for us, there's no wrong solution if it works.

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