10 inch solid tube or 12 inch truss

I am thinking of either buying a 10 inch solid tube Dob or a 12 inch
truss. I understand the portability factor with the 12 inch, but I am
a bit wary of the collimating it. I have used a 10 inch solid tube and
it is easy to collimate.
What about collimating a truss scope such as a Lightbridge?

Also, what would be the height of optical tube with the primary mirror
cell in a 12 inch truss?

Bruce

I am thinking of either buying a 10 inch solid tube Dob or a 12 inch
truss. I understand the portability factor with the 12 inch, but I am
a bit wary of the collimating it. I have used a 10 inch solid tube and
it is easy to collimate.
What about collimating a truss scope such as a Lightbridge?

A well made truss scope is not any harder to collimate than a well made
solid tube scope. However, it may require more frequent collimation in that
you probably will have to tweak it every time you assemble it. One the other
hand, I check my solid tube every time I use it so the only difference would
be that the truss would probably require a little more adjustment - not a
big deal. The 12" is probably a shorter focal ratio, so would be more
sensitive to mis-collimation, but again I collimate my solid tube f/6 scope
well and wouldn't do anything different for one with a shorter focal ratio.
The bottom line is that I wouldn't expect to spend more than 5 minutes on
collimation every time using the scope.


Also, what would be the height of optical tube with the primary mirror
cell in a 12 inch truss?

This varies with the scope, and is a function of the focal length and
optical design. You should check with the manufacturer. However, the length
would be the same as that of a solid-tube with the same optical
design/layout. The truss poles don't change anything, except for replacing
the solid tube and so making disassembly/transporting easier.

My advice is to build your own, using top-notch purchased parts (at least
the primary mirror, secondary mirror, and focuser.) I have never used a
Chinese dob (as sold by all of the usual suspects) that is as nice as a
homemade one. However, I was pleasantly surprised when I read on the cover
of the latest Orion catalog that their new truss tube scope will use Ebony
Star and teflon for the bearings - which is standard in homemade dobs! If
you are unable/unwilling to build your own, then maybe you want to check out
this model. However, even if they build it right there is still the issue of
the optics, and the quality of cheap optics is hit and miss. Who knows,
maybe the optics are great? In my case, the only questionable optics I am
willing to mess around with are those made by me and my sons, and even then
I have my limits! Observing time is too precious to waste on blurry views.

Dennis

Originally Posted by brucegooglegroups

I am thinking of either buying a 10 inch solid tube Dob or a 12 inch
truss. I understand the portability factor with the 12 inch, but I am
a bit wary of the collimating it. I have used a 10 inch solid tube and
it is easy to collimate.
What about collimating a truss scope such as a Lightbridge?

Also, what would be the height of optical tube with the primary mirror
cell in a 12 inch truss?

Bruce

Hi Bruce,

As has already been stated don't sweat the collimation. It will be no harder on the truss tube, but you will need to do it every time you set-up. But if it is well made you should only have to tweak it.

As to length. The 12" Meade Lightbridge is f5 if memory serves me correctly. So 12" or 305 mm at f5 is 12x5=60" or 305x5=1525mm. So the focal length is 5 feet. Then add a bit for the mirror box and base and you are somewhere in the range of 5' 6" to 6' when fully set up. So unless you are really short only at the zenith will the eyepiece be at a difficult position.

One thing to think about though, if you are not observing at a dark site you will also need a shroud for the truss tube. Otherwise the incidental light will really degrade your views.

Clear skies

Hi Dennis,

Also, what would be the height of optical tube with the primary mirror
cell in a 12 inch truss?

This varies with the scope, and is a function of the focal length and
optical design. You should check with the manufacturer. However, the length
would be the same as that of a solid-tube with the same optical
design/layout.

So the optical tube for a truss is about the same as a solid tube. So
what is the advantage? Wouldn't the tube for either a solid or truss
take up the same space in a car?

However, I was pleasantly surprised when I read on the cover
of the latest Orion catalog that their new truss tube scope will use Ebony
Star and teflon for the bearings - which is standard in homemade dobs! If
you are unable/unwilling to build your own, then maybe you want to check out
this model.

Does this telescope look to be well built- as good as other trusses of
the same size? Is the design different than other trusses?

Clear Skies.
Bruce

On Sep 15, 6:39*pm, brucegooglegroups
wrote:

So the optical tube for a truss is about the same as a solid tube. So
what is the advantage? Wouldn't the tube for either a solid or truss
take up the same space in a car?

The space requirement to transport a *disassembled* truss-tubed scope
does not have to be as long as that required for the fully assembled
(or for an equivalent solid-tubed) telescope. One of the primary
advantages of a truss-tubed design is that the tube can be dismantled
for transport within a shorter cargo space.

Does this telescope look to be well built- as good as other trusses of
the *same size? Is the design different than other trusses?

Well built? I haven't heard any first-hand accounts of the Orion
scope, and I've not seen a sample of that scope. So I really don't
know. One of the obvious design differences compared with the
Lightbridges is the number of truss tubes. That difference may be
looked upon by some as an improvement (it's likely to more easily
support a light shroud) and by others as overly redundant (the three
two-tubed truss sections of the Lightbridges appear to hold the
components together adequately). In the absence of any first-hand
accounts the Orion scope looks to be worth trying.

Bill Greer
To sketch is to see.
http://cejour.blogspot.com
http://www.rangeweb.net/~sketcher

In article
,
brucegooglegroups wrote:

snip

So the optical tube for a truss is about the same as a solid tube. So
what is the advantage? Wouldn't the tube for either a solid or truss
take up the same space in a car?

If the latter remains assembled, yes. But most truss tubes (especially
the largest ones) are designed to be broken down for transport, making a
fairly compact bundle of rods -- along with a couple of hat-box-sized
pieces at the top & bottom ends, where all the optical components are
mounted -- and then easily reassembled.

--
Odysseus

Hi Dennis,

Also, what would be the height of optical tube with the primary mirror
cell in a 12 inch truss?

This varies with the scope, and is a function of the focal length and
optical design. You should check with the manufacturer. However, the
length
would be the same as that of a solid-tube with the same optical
design/layout.

So the optical tube for a truss is about the same as a solid tube. So
what is the advantage? Wouldn't the tube for either a solid or truss
take up the same space in a car?

Being able to remove the truss poles and separate the primary mirror
assemble and the secondary cage makes for a much more portable package, and
is a huge advantage of the truss design.


However, I was pleasantly surprised when I read on the cover
of the latest Orion catalog that their new truss tube scope will use
Ebony
Star and teflon for the bearings - which is standard in homemade dobs! If
you are unable/unwilling to build your own, then maybe you want to check
out
this model.

Does this telescope look to be well built- as good as other trusses of
the same size? Is the design different than other trusses?

I don't think we yet know very much about this scope, but if I were in the
market for a dob I would probably postpone any purchase until I could check
it out. Just the fact that Orion says it will use Ebony Star and teflon
doesn't mean very much, but I am an optimistic fellow and so I want to
believe that this indicates attention to good telescope building practices
in general.


Clear Skies.
Bruce

Dennis Woos wrote:
Hi Dennis,

(snip!)

However, I was pleasantly surprised when I read on the cover
of the latest Orion catalog that their new truss tube scope will use
Ebony
Star and teflon for the bearings - which is standard in homemade dobs! If
you are unable/unwilling to build your own, then maybe you want to check
out
this model.

Does this telescope look to be well built- as good as other trusses of
the same size? Is the design different than other trusses?


I don't think we yet know very much about this scope, but if I were in the
market for a dob I would probably postpone any purchase until I could check
it out. Just the fact that Orion says it will use Ebony Star and teflon
doesn't mean very much, but I am an optimistic fellow and so I want to
believe that this indicates attention to good telescope building practices
in general.

I agree that one should attempt to try out a scope before-hand, and
that's what star parties are all about, if members are willing to help.
But Orion also has the well-earned reputation for offering quality
telescopes, so I don't believe you can go wrong with them, if you decide
their scope is the one you want.

As for the arguments for and against both solid tubes and truss, it
depends on how you balance the factors for YOURSELF. Portability means
more mechanical tweaking to get a Newt to work, but it might be worth it
if it reduces weight and gains in aperture, for instance. Are you good
with mechanical things? Even if you can heft a lot, do you want to do
this as a hobby?

Keep these things in mind:

--- The best scope for you is the scope you're going to use the most.
And on that topic . . . .

--- If it gets inconvenient for you to use the scope, you've got a big
paperweight.


--- Dave