Daft Question About Dewbands.

[tich]

Sorry for asking a daft question about these but I've recently built a dew controller & now I need some dewbands. Now what would I need for my 200P & ST80 as I want to attempt some guided images & use it for observing too. I'm guessing I need one to go on the ST80 deshield one for the 200p focuser, but the one I'm stumped on the most is for the secondary mirror as do I need one to go around the aperture of the scope or is there one that attaches to the secondary as I'm sure I've seen one of those? The controller I've built has 4 outlets which I'm sure will be enough, I've got a dewshield on the scope which does help but on a couple of imaging sessions the mirror has still dewed up.

[Tinker1947]

Put a dew shield on the end of the tube, i have a Revelation dew strap on my ST-80 and its stayed crystal clear all night, not bothered with the focusor......My dew shield, the picture is pre ST-80 Dewstrap...

[tich]

Cheers Tinker although with a dew shield on my 200P I still get dew forming on my secondary. It's probably due to my scope being set up on grass as I have no hard standing here to set the scope up on. On my first unguided attempt on the flame nebula I had to delete a load of subs because of the dew.

[Islander]

Secondary dew heaters just lay on the back of the mirror with the lead taped or clipped along one arm of the spider. You can make your own with a few resistors if you're handy with a soldering iron. There's a how to here:

http://www.dewbuster.com/heaters-330ohm_resistors.html

[tich]

Thanks for the link, I may have a go at making one up as I'm not finding much online.

[Cartman]

An even dafter question: how do I know if I need dewbands? Please enlighten me.

[tich]

I only knew due to my secondary mirror misting up when I've attempted some DSO imaging even with a dew shield attached. I haven't attempted guided imaging yet but from what I've read I'll need one on my ST80 too.

[GlassWalker]

An even dafter question: how do I know if I need dewbands? Please enlighten me.

You need a dew heater if you've tried a dew shield and still get dew...

[JamesM]

Tich, Altair Astro sell dew strips made by a company called 'Kendrick', if you take a look toward the bottom of their product page here, you can see some oval orange shaped dew pads here which attach to the secondary. I know that Telescope House also sell this brand too and might be worth giving them a call too.

James

[tich]

That's the one James thanks, I'll just measure up my secondary & get one ordered plus a dew strap for my ST80, hopefully that cure my dewing up woes.

I just love this site...

[RikM]

I don't think they fit SkyWatcher secondary holders do they? Out of interest, does the extra wire along the spider leading from a secondary heater cause any weird diffraction artefacts?

[tich]

According to the site the middle sized one should fit my 200P, I may contact them first & ask them a few questions before ordering one. As for weird diffraction spikes I'll let you know but it's either one of these or a fogged up secondary after a couple of hours as my dewshield just isn't up to it where I am.

[RikM]

You might have to remove the mirror from the holder and then reattach it somehow. I know my 150P and 250PX don't have 'a hollow mirror housing which grips the mirror around the outer edge'. It would be great if they do fit though. I don't have dew problems at home, but at the SGL star parties my secondary always gets fogged up

[tich]

Hmmm well that's given me something to think about & yes I remember being at SGL7 as mine fogged up too, especially when some mist came over in the early hours then 10 minutes later dissapeared. You soon started to hear the 12v hair driers lol.

Unfortunately I have to set up on the lawn so I guess the dew is coming up from the ground easier rather than hard standing. There's a number on the website so I will ring them first but that is the type of thing I'm looking for. I'd imagine a large band around the end of the tube would cause thermal currents so I'd be no nearer solving the problem.

[Tinker1947]

There is this type, a touch on the expensive side so what it is..... http://www.altairastro.com/product.php?productid=16275&cat=243&page=1

[tich]

Yeah that one is a tad pricey especially as it just sticks to the rear of the mirror. Thanks for the link though just a shame they are sold out of this type so I'm still trying to source one.