Shroud advice

[Darkplague]

Okay, I'm finally ready to work on my shroud, and have bought the material for it. Not very fond of the rip-stop material so decided to go with a strechable polyster type fabric like the one in the picture below.

What I would like to know is what is the name of the material they have sewn into the top and bottom of this shroud? It looks like some material you would find on the hems of jumpers.

Also, if I were to substitute this hem material for a drawstring, would I need to use an elastic drawstring or just a normal string?????

[Satchmo]

You don't want stretch polyster becasue it cuts into the light path when tensioned ( study the photo) also it becomes waterlogged with dew and sags into the light path even further. Obsession scopes seem to favor ripstop with a drawstring.

Shrouds don't do anything but stop kids dropping their icecreams on the mirror at star parties Make sure you have the bottom rolled up for a few hours while your mirror is cooling.

Mark

[Darkplague]

Originally Posted by Mark Suchting

You don't want stretch polyster becasue it cuts into the light path when tensioned ( study the photo) also it becomes waterlogged with dew and sags into the light path even further. Obsession scopes seem to favor ripstop with a drawstring.

Shrouds don't do anything but stop kids dropping their icecreams on the mirror at star parties Make sure you have the bottom rolled up for a few hours while your mirror is cooling.

Mark

The Teeter's telescopes use this type of shroud, however I have never heard of any issues with the Shroud blocking the light path. I do see your point though! My truss blocks are out way further than the scope in the picture, so I should be ok.

I would hope that the dew wouldnt make the shroud sag, but only time will tell. From what I've heard, some people have complained about their rip-stop shrouds actually funneling the dew inside their mirror boxes so theres always pluses and minuses with every material I suppose.

BTW I am very happy with the mirror you made me, the detail I saw on the moon the other day with a TAK le 7.5mm, was outstanding. I dont remember seeing such fine detail at all with my 12" GSO.

[Satchmo]

Hi Mark

Congratulations on 'first light' even if your scope was not officially 'finished'.

Yes I'm afraid the stretch polyester will sag quite badly when it gets loaded up with dew. Ripstop will funnel water because it doesn't absorb it much.

You will be able to go down to 3mm FL eyepiece on a really good night. My bench Null star test on your mirror was conducted at 2.5mm FL and the Airy disc still snapped into focus with no mushing . That was with no atmosphere to contend with of course .

Do start an official `its finished' thread when you're happy with everything , I'm sure many people havebeen following your progress .

Mark

[Orion]

Originally Posted by Darkplague

Okay, I'm finally ready to work on my shroud, and have bought the material for it. Not very fond of the rip-stop material so decided to go with a strechable polyster type fabric like the one in the picture below.

What I would like to know is what is the name of the material they have sewn into the top and bottom of this shroud? It looks like some material you would find on the hems of jumpers.

Also, if I were to substitute this hem material for a drawstring, would I need to use an elastic drawstring or just a normal string?????

I use the same material on my scope and never had a problem with dew as long as it fits over the telescope snugly.
I sewed a overlap at both ends and used a draw sting. It certainly makes the telescope look nice with nothing sagging.

The peace of mind in knowing that nothing is going to fall out of someones top pocket for instance like a small torch or a eyepiece, and land on the mirror while they are looking through the eyepiece is well worth the effort.

[AstroJunk (Jonathan)]

As a Queenslander I fight with humidity all the time!

The problem with sagging is near the UTA rather than at the base - One night I hadn't tensioned up the shroud properly and noticed when I did a mid-evening star test that a big chunk (OK, a mild exageration ) of aperture had been taken out by the sagging shroud.

As with Mark; that scope seems to have the same problem designed in permanently - use ripstop or similar and keep the tension up!

[astronut (John)]

I was going to use rip stop nylon for my Lightbridge 12", but in the end I bought the Astrozap shroud. It's made from cotton/ polyester, it also has at each end a plastic strip sewn into the shroud. This helps push out the material so it does not enter the light path.
I also spray 3M water repellant on the shroud, this prevents it from getting dirty and also helps repel water on those dewy nights.
It has draw strings at each end.
I used it through the winter with great results, it also freezes well in those -7 nights we had . Cheers, John.