Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Newtonian dew problem

russ

By russ
in Discussions - Scopes / Whole setups

Recommended Posts

russ

russ

Posted
Posted

Need some advice on dew prevention when using a Newtonian.

My area suffers real bad with the dew. I was out Saturday night, got started at 21.30 and noted how much dew there was on the tube already. By 22.00 the secondary mirror was covered and then by 23.00 the primary was 70% covered. The scope and mount looked like someone had tipped a bucket of water over them.

With an SCT or refractor the problem is easy...buy a heated dew strap and job done. But what do you do with a Newt?

Thanks in advance

Russ

Link to comment
Share on other sites
  • Replies 25
  • Created
  • Last Reply
James

James

Posted
Posted

I've had bad dew but never that bad Russ! I use a dewshield for the front of the scope (one of the Astrozap flexible jobbies) which has stopped my secondary dewing up. My primary dewed up just the once (the secondary was OK) when I'd spent 30 minutes looking at stuff at/near the zenith. I'm guessing it was because cold air was just sinking into the tube and cooling the primary too fast. Not sure what I'm going to do about it but the last couple of times I was out I tended to leave the scope pointed at a much lower altitude between objects in the probably silly belief that cold air wouldn't collect at the bottom of the tube.

James

Link to comment
Share on other sites
jarbi

jarbi

Posted
Posted

rus,

I can second the Kendrick dew heaters, I am heavily using them on the primary, the guide and the finder as well. For the secondary I have built a small heater from resistors.

I can feel with you, because our garden is a bit like your place. In september, when I start observing around 21-22h, the scope gets completely wet within a half hour, and it is impossible to do a longer session without dew heaters. I have a 4-port Kendrick controller to connect all heaters to the 12V power supply, and I can hold on the whole night with it :wink:.

The problem arises only when I need to bring in the scope ;). Then my primary gets also wet because of the higher temperature inside. I still didn't figure out a solution for that...

cheers,

Janos

Link to comment
Share on other sites
russ

russ

Posted
  • Author
Posted

Many thanks Ant for the link.

Ron, i thought about closing it up but the cost isn't an option.

James, yep a dew shield maybe the first option being cheapest. And yes the scope was pointing directly up at M27/M57 to start the evening. That must have been the problem.

Worst dew i've had since 2004. That night even the Kendrick dew heater failed to keep the LX200 corrector clear....even on full pelt! I may as well of got the hose out and drenched the kit.

Thanks again for the replies

Russ

Link to comment
Share on other sites
russ

russ

Posted
  • Author
Posted

Many thanks Janos, i wondered if i was the only with dew problems on a closed tube Newtonian.

I did have the Kendrick 4 port controller but like a fool sold it with

the SCT thinking i wouldn't need it with the Newt.

Had the same problem when i brought the tube indoors. The primary looked like a bird bath. At 1am i decided to strip the scope down, remove the mirrors and bung them in the kitchen sink. Had only gone through the process of cleaning them in the morning, so wasn't about to let them get covered in dew spots. Rinsed them down with distilled water and put them on the drainder for 10mins. Dabbed of the larger water droplets with cotton wool, without touching the mirror. Put the whole lot back together at 2am. Don't fancy doing that everytime there's some dew!

Russ

Link to comment
Share on other sites
russ

russ

Posted
  • Author
Posted
Rus, my C8N seems to be a dew magnet for some reason. I just bought a 12v haridryer, not pretty but it does the job. Besides with the size of your tube you could crawl in there!

Ah yes that's another plan, thanks Tony. I think initially (as it's cheapest) I'll buy a dew shield and hair dryer. Then go for the dew controller and heat pads.

Oh how i miss the joys of APO ownership. Zero maintenance, no worries!

Link to comment
Share on other sites
Kaptain Klevtsov

Kaptain Klevtsov

Posted
Posted

Many thanks Ant for the link.

Ron, i thought about closing it up but the cost isn't an option.

Russ

£28 from FLO gets you clear Baader film (on the filters page) which shouldn't frighten the bank manager too much.

I've seen resistors stuck to the mirror cell (somewhere, can't remember where it was) to warm the primary slightly as well.

Kaptain Klevtsov

Link to comment
Share on other sites
Kenny_10_Bellys

Kenny_10_Bellys

Posted
Posted

My CPC-800 dewed up something chronic the last time out, probably something to do with looking at overhead targets too long and sitting next to a reservoir. The dewshield jsut doesn't cut it in those situations so rather than order an expensive dew-heating system I ordered a car fan heater job from Amazon. It's basically a flat 8-quid hairdryer that runs off a standard fag lighter socket. Job done. ;)

Link to comment
Share on other sites
barkis

barkis

Posted
Posted

A guy I know who owns a 16" f5 Newt. has his tube walls lined with a black velvety fur like material. Even on a cold frosty night if you put your hand inside the tube, it actually feels warm. He has never had a problem with dewing up of his optics. His tube extension is also lined with the same material. I think it was stuck by a PVA Adhesive I have never seen this on any other scope. He takes great care to keep creepy crawlies out of it mind you. :lol:

Ron. :D

Link to comment
Share on other sites
beamish

beamish

Posted
Posted

Actually Ron, you've reminded me of an ozzy chap on another forum who did the same thing just to improve contrast, he also fitted temp gauges to his primary and tube to monitor/control his Peltier cooled scope !! Fantastic mod, though beyond me ! I've used the same black furry stuff on the inside of my dew-cap, got it from a craft suppliers and it's self adhesive.

Karlo

Link to comment
Share on other sites
  • 9 years later...
MarsG76

MarsG76

Posted
Posted

I added 3 fans blowing up behind the main mirror and I have never had the primary mirror dew up since. The secondary on the other hand does need some kind of dew heater, the secondary is the biggest dewing problem.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.