Truss Dob Questions

Hello Gang!

I have a used truss dob I recently aquired. Its my first, so I have lots of
questions, but here's today's:

It came with dark foam pipe insulators on the trusses and a shroud. How
important are either of these items to achieving good views? The foam
particularly is a pain in the @$$. Whats the big deal if these go away?
Must I paint my trusses flat black?

Thanks a bunch,
Ed

The shroud blocks ambient light and helps to keep the mirrors clean. It's
importance depends on your particular viewing conditions. The following
book will answer most of your questions, including why trusses have foam
insulation:

http://www.willbell.com/tm/dobtel.htm

Del Johnson



"Edward" wrote in message
rthlink.net...
Hello Gang!

I have a used truss dob I recently aquired. Its my first, so I have lots
of
questions, but here's today's:

It came with dark foam pipe insulators on the trusses and a shroud. How
important are either of these items to achieving good views? The foam
particularly is a pain in the @$$. Whats the big deal if these go away?
Must I paint my trusses flat black?

Thanks a bunch,
Ed

If you don't want to buy the book to get one or two questions answered,
Let me help...
The foam is not necessary. Perhaps it keeps the observers hands from
freezing to the truss poles when observing in cold conditions.
The shroud is not necessary. It may improve contrast, however.
The idea is to allow only light from what you are observing to enter the
optical
path. This extra, "scattered" light can come from a variety of off-axis
sources, such
as reflective surfaces on your scope, bad edge on the mirror, blah, blah,
blah.
That is why some people put foam on truss tubes, I think. There is a
simpler,
more elegant solution:

I recently saw a scope with black heat-shrink tubing applied to the truss
poles.
Very, very nice appearance. Less scattered light than naked aluminum truss
poles.
I will soon be replacing the truss poles on my scope, and will include
heat-shrink
tubing in the budget.
"Edward" wrote in message
rthlink.net...
Hello Gang!

I have a used truss dob I recently aquired. Its my first, so I have lots
of
questions, but here's today's:

It came with dark foam pipe insulators on the trusses and a shroud. How
important are either of these items to achieving good views? The foam
particularly is a pain in the @$$. Whats the big deal if these go away?
Must I paint my trusses flat black?

Thanks a bunch,
Ed





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Ed,
In daylight, assemble the scope and, without an eyepiece, see what you can
see in the focuser drawtube.

Good baffling: primary mirror and a lot of black

Poor baffling: primary mirror, ground behind primary mirror, mirror box,
rocker box, bearings, ground around telescope, your feet, nice shiny poles,
and the guy set up next to you

I use a plain aluminum pole, but then I remove all sources of stray light
- baffle behind the primary to block light around the mirror
- baffle in front of the primary, blackened
- blackened mirror box
- blackened pole clamps
- blackened poles (at least the inner side, up to where I can't see it)
- black shroud to block light sources beyond the poles
- black baffle under the UTA so I can't see past the far side

You get the idea. In production, foam sleeves and shrouds are cheap and
effective.

Have fun,
Frank

"Edward" wrote in message
rthlink.net...
Hello Gang!

I have a used truss dob I recently aquired. Its my first, so I have lots
of
questions, but here's today's:

It came with dark foam pipe insulators on the trusses and a shroud. How
important are either of these items to achieving good views? The foam
particularly is a pain in the @$$. Whats the big deal if these go away?
Must I paint my trusses flat black?

Thanks a bunch,
Ed

True, and all good points, BUT you start making changes to probably
a perfectly good scope that the previous owner had tweaked to his
own perfection,......you start making changes, like remove the foam
from the poles, and now you'll find that the shroud no long fits
tight around the poles,
And now the poles now vibrate. Also you may now be out of balance.
So now you have them coated and stuffed with
polyester fiberfill to dampen the vibration, so NOW the scope is top
heavy, so you have to start counterbalancing....now you find the bottom
of the scope hits the rocker box, so you have to rebuild the rocker
box, and get a seamstress to take up the slack in the shroud....it
goes on and on.....make one little change, thinking that nothing
else is affected, and boy, you could be in for a surprise.

Why not use it as is for a few months, until you get used to it...
I mean the original owner must have had those foams on there for a good
reason....just remember, you make one little change to a truss DOB,
there will be other changes somewhere else, required; you can bet on that!!

The shroud serves 4 functions; keeps stray light out...may help dampen
vibration in trusses, keeps dust of your mirrors, keeps body heat from
entering the optical plane, and with fans at bottom of mirror, helps
keep your secondary mirror from dewing up as fast as it might if it
were not for a shroud (by keeping heat slowly moving up the 'tube'
Clear Skies,
Tom W.

PS....go ahead...paint your trusses flat black...but then, a year or
two from now, don't complain to us when you see little chips (or dust)
of black paint down on your primary mirror. (That's why I don't paint
them).



Edward wrote:
Hello Gang!

I have a used truss dob I recently aquired. Its my first, so I have lots of
questions, but here's today's:

It came with dark foam pipe insulators on the trusses and a shroud. How
important are either of these items to achieving good views? The foam
particularly is a pain in the @$$. Whats the big deal if these go away?
Must I paint my trusses flat black?

Thanks a bunch,
Ed

On Thu, 10 Jul 2003 17:22:53 GMT, "Edward" wrote:

Hello Gang!

I have a used truss dob I recently aquired. Its my first, so I have lots of
questions, but here's today's:

It came with dark foam pipe insulators on the trusses and a shroud. How
important are either of these items to achieving good views? The foam
particularly is a pain in the @$$. Whats the big deal if these go away?
Must I paint my trusses flat black?

Thanks a bunch,
Ed


Ed:

The foam tubes have a few uses. They stop vibrations from getting to
the EP. They also keep your hands off the cold tubes. Yes, the black
helps too.

The shroud keeps dropped items from hitting your primary, keeps stray
light out of the optical path, and some say it keeps the heat from
your body from entering the light path.

I'd use both.


Space Traveler

Thank you Del, etok, Len, Frank, Tom. I posted to avoid unintended
consequences and I think I have. Mental notes: shroud = cleaner mirror,
investigate heat shrink tubing, watch out for truss vibrations, think
through baffling, dew and temperature issues.

Is the black foam available in smaller diameters? I think my biggest issue
is that the trusses are quite a bit smaller than the I.D. of the foam and
they slip out, making them less than ideal to handle . They are 1" O.D.
from Moonlight Instruments. Where can I shop for smaller diameter foam
tubes? Where is that heat-shrink stuff sold?

The scope is an 8" f8 with a Royce mirror and my only issues are ergonomics
and balance. I would only modify it after a great deal of fore thought.
Thanks a lot,
Ed


"Edward" wrote in message
rthlink.net...
Hello Gang!

I have a used truss dob I recently aquired. Its my first, so I have lots
of
questions, but here's today's:

It came with dark foam pipe insulators on the trusses and a shroud. How
important are either of these items to achieving good views? The foam
particularly is a pain in the @$$. Whats the big deal if these go away?
Must I paint my trusses flat black?

Thanks a bunch,
Ed

"Edward" wrote in message news:WwyPa.41471

Is the black foam available in smaller diameters? I think my biggest
issue
is that the trusses are quite a bit smaller than the I.D. of the foam and
they slip out, making them less than ideal to handle . They are 1" O.D.
from Moonlight Instruments. Where can I shop for smaller diameter foam
tubes? Where is that heat-shrink stuff sold?
Ed

Well I replaced my foam tubing Friday. I found some for 3/4" copper pipe
that has a 7/8" I.D. and it fits much tighter than the tubing for 1" copper
pipe (1 1/8" I.D.). Got it at Home Depot. Thanks again to all who offered
advise.

Ed