C-11 or 13" Truss-DOB, that is the question...

I have a 13" Coulter mirror set, 1/10 wave, I was going to build a
truss-DOB. But, now I got a very nice C-11 OTA, that I use on my GiroII
mount. Pritty smooth.
Which one is better.? Should I make the effort to finish the 13" truss-DOB?
My thinking is, that 13" not going to show much more than the C-11. Is there
any reason the 13" truss-DOB is better than the C-11, like cooling time,
sharpness, portability etc..?

Thanks, Julius

My thinking is, that 13" not going to show much more than the C-11. Is there
any reason the 13" truss-DOB is better than the C-11, like cooling time,
sharpness, portability etc..?

Thanks, Julius

A couple of things to consider..

1. That 13.1 inch will have about 40% more mirror area, not insignificant when
combined with simpler optics and fewer surfaces.
2 Focal length. Don't know what your DOB is but if it is F4.5 then it will
have a 1500mm focal length, the C11 will be about 2800 mm. One can use a focal
reducer to bring that 2800mm down to 1800mm, not too bad, I don't know what
happens when you combine a 2 inch eyepiece with a focal reducer on a C-11, if
it works, then you should be able to get almost the FOV of the DOB.

jon

My thinking is, that 13" not going to show much more than the C-11. Is there
any reason the 13" truss-DOB is better than the C-11, like cooling time,
sharpness, portability etc..?

Thanks, Julius

A couple of things to consider..

1. That 13.1 inch will have about 40% more mirror area, not insignificant when
combined with simpler optics and fewer surfaces.
2 Focal length. Don't know what your DOB is but if it is F4.5 then it will
have a 1500mm focal length, the C11 will be about 2800 mm. One can use a focal
reducer to bring that 2800mm down to 1800mm, not too bad, I don't know what
happens when you combine a 2 inch eyepiece with a focal reducer on a C-11, if
it works, then you should be able to get almost the FOV of the DOB.

jon

My thinking is, that 13" not going to show much more than the C-11. Is there
any reason the 13" truss-DOB is better than the C-11, like cooling time,
sharpness, portability etc..?

Depends what you want to do. The Coulter will give you more light gathering
power, enough to notice over the C11 from a dark sky. A better scope for deep
sky observing. Is your mount for the C11 motor driven? If so, it would be
better if you're into lunar/planetary/double star observing.

Richard Navarrete

Astrophotography Web Page - http://members.aol.com/richardn22

My thinking is, that 13" not going to show much more than the C-11. Is there
any reason the 13" truss-DOB is better than the C-11, like cooling time,
sharpness, portability etc..?

Depends what you want to do. The Coulter will give you more light gathering
power, enough to notice over the C11 from a dark sky. A better scope for deep
sky observing. Is your mount for the C11 motor driven? If so, it would be
better if you're into lunar/planetary/double star observing.

Richard Navarrete

Astrophotography Web Page - http://members.aol.com/richardn22

Right now, I use the GiroII Alt-AZ mounted on my GP legs, with a short pier.
Quit stable and smooth. Later I can add an EQ mount, like the CI-700, in
case of photography bug.

Julius


"RichardN22" wrote in message
...
My thinking is, that 13" not going to show much more than the C-11. Is
there
any reason the 13" truss-DOB is better than the C-11, like cooling time,
sharpness, portability etc..?

Depends what you want to do. The Coulter will give you more light
gathering
power, enough to notice over the C11 from a dark sky. A better scope for
deep
sky observing. Is your mount for the C11 motor driven? If so, it would
be
better if you're into lunar/planetary/double star observing.

Richard Navarrete

Astrophotography Web Page - http://members.aol.com/richardn22

Right now, I use the GiroII Alt-AZ mounted on my GP legs, with a short pier.
Quit stable and smooth. Later I can add an EQ mount, like the CI-700, in
case of photography bug.

Julius


"RichardN22" wrote in message
...
My thinking is, that 13" not going to show much more than the C-11. Is
there
any reason the 13" truss-DOB is better than the C-11, like cooling time,
sharpness, portability etc..?

Depends what you want to do. The Coulter will give you more light
gathering
power, enough to notice over the C11 from a dark sky. A better scope for
deep
sky observing. Is your mount for the C11 motor driven? If so, it would
be
better if you're into lunar/planetary/double star observing.

Richard Navarrete

Astrophotography Web Page - http://members.aol.com/richardn22

Julius,

If you have not yet built the truss Dob, the C-11 you just acquired
precludes the need to do so. I can tell you that the C-11 is just about as
good as SCTs get. While the SCT has a long list of advantages over the Dob,
it also has a list of disadvantages. You have to decide which of the 2
scopes are better suited for you. Now if you ask me what I think, I would
say sell the Coulter mirror set and stay with the SCT...but then I love
SCTs.

Al


"Szaki" wrote in message
news:lMRVb.265311$na.420085@attbi_s04...
I have a 13" Coulter mirror set, 1/10 wave, I was going to build a
truss-DOB. But, now I got a very nice C-11 OTA, that I use on my GiroII
mount. Pritty smooth.
Which one is better.? Should I make the effort to finish the 13"
truss-DOB?
My thinking is, that 13" not going to show much more than the C-11. Is
there
any reason the 13" truss-DOB is better than the C-11, like cooling time,
sharpness, portability etc..?

Thanks, Julius

Julius,

If you have not yet built the truss Dob, the C-11 you just acquired
precludes the need to do so. I can tell you that the C-11 is just about as
good as SCTs get. While the SCT has a long list of advantages over the Dob,
it also has a list of disadvantages. You have to decide which of the 2
scopes are better suited for you. Now if you ask me what I think, I would
say sell the Coulter mirror set and stay with the SCT...but then I love
SCTs.

Al


"Szaki" wrote in message
news:lMRVb.265311$na.420085@attbi_s04...
I have a 13" Coulter mirror set, 1/10 wave, I was going to build a
truss-DOB. But, now I got a very nice C-11 OTA, that I use on my GiroII
mount. Pritty smooth.
Which one is better.? Should I make the effort to finish the 13"
truss-DOB?
My thinking is, that 13" not going to show much more than the C-11. Is
there
any reason the 13" truss-DOB is better than the C-11, like cooling time,
sharpness, portability etc..?

Thanks, Julius

I have a 13" Coulter mirror set, 1/10 wave, I was going to build a
truss-DOB. But, now I got a very nice C-11 OTA


Hi:

Well, a 1/10 wave Coulter mirror set is certainly a rara avis...but...no, it
won't show you much more than what the 11 will, and perhaps less on the
planets. Nice project, though.


Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html