What sort of fabric is considered appropriate for a light shroud on a truss scope?
I have a Skywatcher dob, with the three rod extending tube design, which can be tricky because if the fabric is stretched around the circumference of the tube it will form a triangle and partly obstruct the light path.
If I attach it (via Velcro) to the circular tubes so the fabric is relatively taut when the tube is fully extended it will work, but when the fabric loses its elasticity it would again sag in the light path, so I suspect a stretchy elastic t-shirt type of fabric would not last very long.
I have been trying to look for a photo of my set-up which is a Skywatcher. Cant find it.
Place is still a mess so cant find it yet either, but i used stretchy material but be careful of flaking of the material when it is cut.
I used 2 or 3 wooden stiffening post only 10mm wide and the length of the extensions to mount the material and finally used Velcro to attach it to the rods and stretch it around meeting back at the starting rod and Velcro attaching to the rod.
This is not exactly right as I haven't used the scope for quite some time. I will try to locate it and take a photo, but it really helped when I used to take lunar shots. The bright moonlight would shine in via the side and blow out the pictures.
I used circles of plastic 'cable snake' to form hoops attached by adhesive velcro to my 16" GSO Strut Dob. Just two hoops were enough to prevent shroud sag into field of view. They sell 'cable snake' on ebay. I spray painted the snake black, and the two end can be put together with a short garden hose splice, adhesve velcro from Bunnings. I know other IIS members have used the same technique.
As to shroud material, I bought a custom fit shroud from Astrozap, i'd look there first as they make them for most production scopes. For custom shrouds on the 10" newt I built I just used Lycra, It's stretch enough to give a good tight fit with no sage but can allow a bit of light through the 'pores' but usually only perpindicular to the scope sides.
I made my light shroud from some heavy cotton / linen material and 25mm plastic square garden lattice from Bunnings. The material happens to be green because the day I went shopping I couldn't find any black.
This square lattice product keeps the tubular shape well when fitted, and it bends easily enough so that if you are looking through a straight-through finderscope, you can get into position comfortably without pushing the OTA all over the place place with your cheek. (My Mk1 version used core flute which didn't bend easily).
You will need much less than the amount in the smallest packaged roll. Maybe someone in your astronomy group has some spare.
I folded the top of the shroud over and sewed it so I could thread a long length of nylon string - the excess is wrapped around the OTA to cut off any gaps during Solar viewing.
The top flap of the shroud is held closed first with a velcro patch.
Spotlight sells black rip-stop nylon which is strong and dense. I'm not sure shrouds make much difference though if you get the baffling right on the secondary cage and a focuser baffle of the appropriate dimensions.
We used an Astrozap shroud (for another scope) as a guide and tried to copy the construction as close as we could.
Black medium density material (non stretchy).
Sewed two "pockets" into the body to take two plastic strips.
Sewed draw strings into each end.
But consider how much material you will need, eg to allow it to fit over the scope with the focuser still in place. (but probably not the finder scope), because the more material there is, the more likely it will sag into the light path, especially if it gets heavy with dew.
I have seen others using "yellow tongue" as the ribs, but they had to be fixed in place each time.
My design is quick and simple use (but not quick or simple to make).
It certainly has proved effective here where the dew has been extra bad lately. But where dew is not a problem, (nor stray light) it is better without a shroud as far as cooling and thermal currents are concerned.
I took some photos of my shroud but as my scope is too well stored away I can take and image of it.
It was a rough 40 minute put together but it is functional.
1 - all rolled up only 30mm diameter, easy to store.
2 - unrolled has 3 pieces of wood Velcro'ed directly on the Skywatcher upper and lower scope tube when extended. These posts prevent the material cutting into the inner tube blocking the light path.
3 - 2 more stick provide the rigid start and end point with Velcro tying them together. Start and finish points are on the Skywatcher posts.
I have not used the scope for a while so I wont be pulling it out until I am ready to use it or change it.
Edit: The material is doubled over to decrease the light throughput.
Hey there,
My first attempt was using three pieces of dowel and some black fabric but it turned out a bit dodgy (first 2 photos were during the construction of it). So then I went to Clark Rubber and got Formsheild and made a cylinder (joining it with insulation tape from Bunnings), these are the last three pictures. Its light, holds its shape, and is very easy to pop in or out of the scope and sits there all night.
Cheers.
