Westmoorland Posted September 18, 2022 Share Posted September 18, 2022 I thought pointing an SCT downwards gets rid of the dew? I also pointed the eyepiece downwards and that's fogged up. I shined a torch at the corrector plate and on top of the dew it's covered in obscene looking smudges despite me never touching the thing. I don't think I'll bother putting the dew shield on again. How do you get past this stage? Link to comment Share on other sites More sharing options...
Stu Posted September 19, 2022 Share Posted September 19, 2022 2 hours ago, Westmoorland said: I thought pointing an SCT downwards gets rid of the dew? I also pointed the eyepiece downwards and that's fogged up. I shined a torch at the corrector plate and on top of the dew it's covered in obscene looking smudges despite me never touching the thing. I don't think I'll bother putting the dew shield on again. How do you get past this stage? No, pointing it down helps prevent dew forming when it is cooling or you are not using it. I would look into getting a heated dew shield if I were you, plus potentially a 12V hairdryer to clear it if it gets bad. Some nights are much worse than others for dew too, but with a big SCT you generally always need to be prepared for it. Link to comment Share on other sites More sharing options...
Mr Spock Posted September 19, 2022 Share Posted September 19, 2022 I'd go for the hairdryer option. With SCTs dew heaters tend to create tube currents and low level 'tremor' in the image. I saw a good lecture a few years ago by Damien Peach where he detailed all this. With a hairdryer the effect on the scope is only temporary. 2 Link to comment Share on other sites More sharing options...
Elp Posted September 19, 2022 Share Posted September 19, 2022 If it's a Celestron I use their custom dew heater rings which replace the ring sitting on the outer edge of the corrector plate. Works wonders, removed the dewed over plate in less than five minutes, combined with a dew shield didn't dew over again. Link to comment Share on other sites More sharing options...
Westmoorland Posted September 19, 2022 Author Share Posted September 19, 2022 Thank you, all. Looks like a hair dryer until I can be sure my Celestron lithium power tank can power the scope and a dew heater at the same time: I've got a nasty feeling it won't. Link to comment Share on other sites More sharing options...
Elp Posted September 19, 2022 Share Posted September 19, 2022 The ring uses a 12v input, if you were using a power unit box or an Asiair pro/plus it would work via the 12v outs. Link to comment Share on other sites More sharing options...
Westmoorland Posted September 19, 2022 Author Share Posted September 19, 2022 7 minutes ago, Elp said: The ring uses a 12v input, if you were using a power unit box or an Asiair pro/plus it would work via the 12v outs. The Celestron lithium battery ought to be all I need for visual. I'll resist extra box/units for as long as I can. I won't have anywhere to put them. Link to comment Share on other sites More sharing options...
Cosmic Geoff Posted September 20, 2022 Share Posted September 20, 2022 I have found that dew settles preferentially on upward facing surfaces. I always use a dew shield and find this is adequate 99% of the time. More condensation-prone locations may require adopting heated solutions in addition. Link to comment Share on other sites More sharing options...
Merlin Posted September 20, 2022 Share Posted September 20, 2022 The point is to make the shield long enough. Three times the aperture works for me. Link to comment Share on other sites More sharing options...
bemak187 Posted September 23, 2022 Share Posted September 23, 2022 On 19/09/2022 at 09:36, Elp said: If it's a Celestron I use their custom dew heater rings which replace the ring sitting on the outer edge of the corrector plate. Works wonders, removed the dewed over plate in less than five minutes, combined with a dew shield didn't dew over again. Next on my list for my 11 inch. Glad to hear they work well. Link to comment Share on other sites More sharing options...
Elp Posted September 23, 2022 Share Posted September 23, 2022 1 hour ago, bemak187 said: Next on my list for my 11 inch. Glad to hear they work well. Bear in mind mine is a C6 so it clears up faster than a larger scope I presume. Link to comment Share on other sites More sharing options...
beamish Posted September 24, 2022 Share Posted September 24, 2022 On 19/09/2022 at 09:36, Elp said: If it's a Celestron I use their custom dew heater rings which replace the ring sitting on the outer edge of the corrector plate. Works wonders, removed the dewed over plate in less than five minutes, combined with a dew shield didn't dew over again. Are you able to throw some light my way... Ive bought one of the celestron heater ring to work with my Kendrick controller but my plugs are in the opposite position to images on the manual pdf. I dont want to blow it 😉 So plse confirm which is the "power socket" Link to comment Share on other sites More sharing options...
beamish Posted September 24, 2022 Share Posted September 24, 2022 Fwiw, when i was using the C11 i had a custom heater band placed around the front cell and a shield, never once had a problem with dew again. Link to comment Share on other sites More sharing options...
Elp Posted September 24, 2022 Share Posted September 24, 2022 1 hour ago, beamish said: power socket It's the one with the male upstanding pin in the centre, it's physically impossible for a 5.5mm/2.1mm jack 12v cable to plug into the thermistor control one looking at it. Link to comment Share on other sites More sharing options...
beamish Posted September 24, 2022 Share Posted September 24, 2022 Cheers, 👍👍 Link to comment Share on other sites More sharing options...
LukeSkywatcher Posted November 8, 2022 Share Posted November 8, 2022 (edited) On 19/09/2022 at 08:27, Mr Spock said: I'd go for the hairdryer option. With SCTs dew heaters tend to create tube currents and low level 'tremor' in the image. I saw a good lecture a few years ago by Damien Peach where he detailed all this. With a hairdryer the effect on the scope is only temporary. That's actually really good advice. I'd never of thought about it like that. I do have a dew heater, but will buy a small travel hair dryer. Good old Damien Peach. Edited November 8, 2022 by LukeSkywatcher Link to comment Share on other sites More sharing options...
dweller25 Posted November 8, 2022 Share Posted November 8, 2022 (edited) @Westmoorland Try wrapping the OTA with 2 layers of reflectix from B&Q 👍 Edited November 8, 2022 by dweller25 1 Link to comment Share on other sites More sharing options...
cjdawson Posted November 8, 2022 Share Posted November 8, 2022 I'm a bit late to this party, but want to give my experiences anyway. SCT's are very likely to dew up if prevention isn't applied straight away. Here's how I do it. 1. Dew Shield. This is a must, don't use the scope without one, it will slow the heat radiation by a significant amount. Which will mean that part two doesn't need to work as hard. 2. Dew heater. You can get or make (I made) a dew heater that sits in front of the correctly plate, and provides enough heat to replace the energy lost even with the shield in place. This will prevent dew from forming, but at the same time allow the scope to cool to get stable images. 3. We all get caught out, so get a 12v hair dryer. This can be used in the event that you had the heater on too low, and the the optics misteded up anyway. It's a last resort, but one that's handy to keep on hand should it be needed. I find that the combination of 1 and 2, sorts out 90% of observiing sessions, even when everything else gets soggy. As for eyepieces, keep them in your pocket when not in use and that'll keep 'em warm. 2 Link to comment Share on other sites More sharing options...
knobby Posted December 18, 2022 Share Posted December 18, 2022 (edited) @cjdawson Hi, do you have any images of your dew heater ? I'm DIY ing something at the moment and had considered placing it inside the front lip but thought it would stop the cap fitting and also make electrical connections difficult. Cheers Edited December 18, 2022 by knobby Link to comment Share on other sites More sharing options...
newbie alert Posted December 19, 2022 Share Posted December 19, 2022 Corrector plates are a magnet for dew, dew shield and a dew heater sorts it out... Found hair drying method is only short term and your focus changes for a few mins after applying, so you have to wait a while it sorts itself out, then repeat once dew forms again Link to comment Share on other sites More sharing options...
bosun21 Posted December 20, 2022 Share Posted December 20, 2022 For the 12v hairdryer make sure you have a heavy enough 12v supply. Around 15A Link to comment Share on other sites More sharing options...
cjdawson Posted December 21, 2022 Share Posted December 21, 2022 On 18/12/2022 at 22:33, knobby said: @cjdawson Hi, do you have any images of your dew heater ? I'm DIY ing something at the moment and had considered placing it inside the front lip but thought it would stop the cap fitting and also make electrical connections difficult. Cheers I’m sure that I have some pictures somewhere. I’m on holiday at the moment so can’t take any fresh pictures at the moment. From what I remember the heater that I made is constructed like this…. 1. NiChrome wire (resistance wire) as the heating element. Run 12v through, at 100% duty cycle, I think it worked out to be about 30 watts of heating. (About 2.4 amps). Though in reality, I run it from a PWM, and normally at less than 50% duty so keeps my scope clear even on the soggiest nights. 2. The wire is threaded through heat shrink tubing, with the ends poking out, the ends are connected to another wire, think I used a solder, but it’s mainly a mechanical joint. Wasn’t happy with this and would do something different next time… though it’s lasted for years without issues. 3. The wire with heat shrink is then threaded through copper brake pipe. 4. The pipe was then bent to form a circle. 5. finally spray painted matte black. The whole thing is held in place on the SCT by pressure alone. the ends of the heater wire are simply taped to the side of the Ota, and run down to a phono plug which connects to the PWM (Heater controller). If I find out a piccy, I’ll post it here later 1 Link to comment Share on other sites More sharing options...
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