What light shroud material?

[alfingido]

I was out last night with the 12"flexidob and after about an hour, the secondary dewed up.

I need a light / dew shroud, but being of Scots descent, dont want to spend £70+ on a shop bought one.

I read another post where neoprene was used, but I was looking for something lighter, similar to the Astrozap design, that i can leave on all the time, up or down.

So, what sort of fabric? Rip stop / tent type fabric will collect moisture, so I need something more absorbent that will not let water run off it but dry off quickly.

Any ideas?

I have a Mother in Law at home with a sewing machine just waiting for something to make!

Allan

[acey]

I have the Astrozap shroud on my 12" flextube and it doesn't stop the secondary from dewing - you need a dewshield (camping mat) for that. And because standard camping mats aren't wide enough (so you can't make the dewshield the necessary 18"+ long), you may still get some dewing with the dewshield. I take a hairdryer with me.

On the flextube a shroud is useful to prevent primary dewing, as a light shield, and to protect the primary from anything you drop. The Astrozap shroud is made from a fairly thick, heavy material - it gets very wet during use and needs to dry off afterwards.

I made a shower-cap-type cover for the bottom end (to further prevent primary dewing) using waterproof breathable nylon (like tent material) which is a lot lighter than the Astrozap material, and quite stiff. I'd rate it poorer than the Astrozap material but reckon it would still be suitable for a shroud. I've seen ripstop nylon often mentioned as a suitable shroud material.

If you're making a shroud then you'll need to put hoops in it so it won't sag into the light path (the Astrozap has two broad strips of plastic).

In breezy conditions a shroud acts like a sail. First time I used mine, the wind was strong enough to blow the shroud into the light path, and blew the scope off-target. Though you tend not to get dew when it's breezy.

[alfingido]

Thanks for the info acey, certainly food for thought. I may go down the neoprene path then, I can leave the dob extended most of the time so a stiffer shield won't be a problem

what sort of camping mat do you refer to for the dew shield? I have a light sheild for the top ( came free with the dob). I' m sure I can modify that

Allan

[callump]

There is merit in additional light shielding around the top hat, but to stop dewing of the secondary you would be better to invest in a dew heater... imho.

/callump

[Doc]

Read this thread might be useful.

http://stargazerslounge.com/diy-astronomer/87098-home-made-light-shroud.html

[acey]

The dewshield is basically a standard foam sleeping mat, cut to wrap around the top of the dob tube. By cutting holes to accomodate the spider and finder fittings, and adding a couple of strips of velcro, I find mine stays on nicely - though it really should extend further beyond the top of the dob to be effective. A dew heater is a more reliable if more complicated option.

Neoprene wouldn't be my shroud material of choice as it's really for situations requiring waterproofing and heat insulation (like my fishing waders). No doubt it would work, but I would have thought that a couple of foam camping mats around the open part of the tube might be equally effective, possibly lighter and cheaper. I've seen spandex touted as a suitable material, also parachute nylon (maybe that's just the same as ripstop).

For convenience, a light, flexible fabric is the way to go - probably just about anything, as long as it's black.

[Beulah]

You could probably buy a black blackout blind from Argos, rip the roll top off the end (just a long cardboard tube I think), and modify it for a light shroud. £14.99....in theory it has insulating properties when hung at the window...

Buy 4ft Thermal Blackout Roller Blind - Black. at Argos.co.uk - Your Online Shop for .