Observatory Mounts

What observatory mounts could be used for a Dobsdonian that could be
computer controlled?

"Macro" wrote in message
ps.com...
What observatory mounts could be used for a Dobsdonian that could be
computer controlled?


The term "Dobsonian" describes a mount, not a telescope. What we commonly
call a "Dobsonian reflector," a "Dobsonian," or a "Dob" is actually a
Newtonian reflector on a Dobsonian mount.

If you want to use a reflector in your observatory, you could mount it on a
motor-driven equatorial mount.

Go to the Orion Telescopes website and look at their reflector scopes:
These are "Dobsonians:"
http://www.telescope.com/jump.jsp?it...EGORY&itemID=9

And these are reflectors mounted on equatorial or alt-az mounts (except for
the StarBlast, which is a miniature Dob):
http://www.telescope.com/jump.jsp?it...List=&oldList=

The optical tube assemblies (OTA) are the very same for the Dobs or for the
equatorial mounted scopes.

Macro posted:

What observatory mounts could be used for a Dobsdonian that could be
computer controlled?

Well, the term "Dobsonian" often refers to a Newtonian on a simple
altitude-azimuth or "altazimuth" mount, moving much like that of a gun
turret on a ship. The mount is not really an "observatory mount" so
much as it is a simple altazimuth with open-faced altitude bearings and
a rocker-box to hold the bearings and to provide rotation on the azimuth
axis. Some moderate to large aperture Dobsonians can be computer
controlled via the Argo-Navis Digital Telescope Computer system:

http://www.wildcard-innovations.com.au/

Some can also be equipped with the SERVOCAT drive system which allows
for both Go-To operation as well as tracking in the altazimuth mode.

http://www.webstertelescopes.com/servocat.htm

Clear skies to you.


--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 14th Annual NEBRASKA STAR PARTY *
* July 15th-20th, 2007, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Joe S. posted:

The term "Dobsonian" describes a mount, not a telescope. What we commonly
call a "Dobsonian reflector," a "Dobsonian," or a "Dob" is actually a
Newtonian reflector on a Dobsonian mount.

Actually, the word "Dobsonian" has evolved over time and has never
really been formally defined. It is frequently used to refer to both
the entire telescope system (a Newtonian on a simple altazimuth mount)
as well as for the mount, although few refractors that are mounted
altazimuthly using the Dob-style mount are referred to as "Dobsonians".
Technically, the mount should be called an altazimuth, although
Dobson's simple design does put in some interesting wrinkles into the
altazimuth, like the open-faced altitude bearings and simple rocker-box
azimuth motion. Many companies refer to their altazimuth Newtonians as
"Dobsonians", rather than Newtonians on a Dobsonian mount. Clear skies
to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 14th Annual NEBRASKA STAR PARTY *
* July 15th-20th, 2007, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

David Knisely wrote:
Actually, the word "Dobsonian" has evolved over time and has never
really been formally defined.

Yup--and is a point of some contention with folks. Going by what people
actually seem to mean when they use the term, rather than what people
think it ought to mean, it's a Newtonian on a rocker-box altazimuth
mount that rests on the ground (or possibly on a platform). Other
optical tubes seem to be said to be on a Dobsonian-style mount, or (as
you say) simply an altazimuth mount.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html

On Sep 11, 4:07 pm, Macro wrote:
What observatory mounts could be used for a Dobsdonian that could be
computer controlled?

Some of this may go over your head; but just file it away for future
reference as you look at mount options. If you go the route of
converting your Dob mounted Newt to a German equatorial mount (GEM),
you'll need the info in the future.

Newts can be removed from their alt-az boxes and converted for
mounting on a GEM.

WRT German equatorial mounts and a 10" Newt, I using a Synta EQ6 -
which is the manufacturer's name for Orion's branded Altas EQ6 mount.
( http://www.skywatchertelescope.com/EQ6SkyScan.html ) This is a
lower cost-end mount with good tracking ability. This mount can be
computer controlled through a laptop by most planetarium programs
through the ASCOM open source telescope interface. (
http://ascom-standards.org/index.html ) In general, ASCOM emulates a
Celestron Nextstar 5i, 8i or Ultima - which can be used by most
planetarium programs. The only hardware add-on usually is a Belkan
USB to serial converter. ( http://www3.shopping.com/xPO-Belkin-...pter-F5U409-CU
)

The 10" Newt did not auto-target properly out of the box using the
Syntax EQ6 mount. An additional extra-heavy duty mounting bar ($175)
had to be purchased to reduce tube and mounting bar flexure that
prevented good perpendicular alignment. The mount will probably work
out of the box with a lighter 8" Newt and is very popular for
astrophotography using relatively lighter 5 1/4 to 6 inch refractors
because of its good tracking ability. If you buy this mount, make
sure you purchase only a newer model with a hand-controller with
version 3.10 software or higher. Used Syntax EQ6s mounts with
pre-3.02 handcontrollers can not be software upgraded and have a
defective hand-controller software design (non-synching dedicated
communications mode). The pre-version 3.02 hand-controller cannot be
used effectively when connected to a laptop program.

In general, Newts take more aligning effort and skill to properly
remove perpendicular error and to keep the scope properly aligned - as
compared to SCTs or refractors. This is because the Newt mirror is
tilted slighty off-axis relative to the physical tube. The objective
in SCTs and refractors are not tilted and the optical axis and the
tube exterior are both parallel to the optical axis.

Celestron's analgous computer-controlled product is the more expensive
CGE mount. ( http://www.celestron.com/c2/product....D=16&ProdID=93
) I am not personally familiar with that GEM mount but have heard
good comments about and seen good performance of this mount at star
parties. I am not sufficiently familar with Meade products to identify
their GEM version.

There is a price vs. tracking error trade off. Spend more money - get
less tracking error. That's an economic selection that you have
make. To some extent, modern low-end autoguiding mounts can
adequately compensate for tracking error during astrophotography to a
degree that makes them a performance alternative to higher-end
mounts.

For auto-guiding, a Guidedog USB autoguiding adapter is added to the
Synta EQ-6 (or other GEM) mount. ( http://www.barkosoftware.com/GuideDog/
)

This autoguiding product is not directly compatible with autoguiding
feature of Meade's imaging software, e.g. Envisage. Third-party
freeware add-ins will let you autoguide on-axis through the Meade
software - ported through the ASCOM interface and the Guidedog USB
adapter. Typically, a second off-axis scope and a separate web camera
are used for autoguiding Newts, rather than on-axis guiding.

- Canopus

Brian Tung wrote:
David Knisely wrote:
Actually, the word "Dobsonian" has evolved over time and has never
really been formally defined.

Yup--and is a point of some contention with folks. Going by what people
actually seem to mean when they use the term, rather than what people
think it ought to mean, it's a Newtonian on a rocker-box altazimuth
mount that rests on the ground (or possibly on a platform). Other
optical tubes seem to be said to be on a Dobsonian-style mount, or (as
you say) simply an altazimuth mount.

Hi, Brian and David.

Maybe there's a variety of usages here also found in other areas. For
example, to most people, a "bulldozer" means the whole vehicle, both the
tractor and the bulldozer attachment. To someone in the trade, however,
it would be more precise to speak of a "tractor-bulldozer," with the
term "bulldozer" properly referring to the attachment.

Similarly, the term "Dobsonian" might more properly refer to the mount,
typically used for a Newtonian but possibly for some other kind of OTA.
However, like "bulldozer," Dobsonian has come often to mean the whole
telescope, including a specifically Newtonian OTA plus the mount.

Dobson himself prefers "sidewalk telescope," which presumably relates
to mount and OTA together -- so that if people thought, "Dobson's
sidewalk telescope," and from there "Dobsonian telescope," then using
the term for the whole telescope as well as the mount would seem
logical.

The other side, of course, is that it's the mount that's more
_distinctively_ "Dobsonian," since Newtonian reflectors had a rather
long history before Dobson championed the design that bears his name.

An interesting question is whether "Dobsonian" has any connotations
that attach to the type of Newtonian OTA involved -- that is, things
not inherent in the definition, but often suggested by it.

One thing I'd suspect people often associate with a "Dobsonian" is
relatively fast optics, or a rich-field telescope, say f/7 or faster.
Maybe this was especially characteristic of the large Dobsonians
that became practical in the first decades of the design on the
amateur market (e.g. Coulter, discussed in another thread). Of
course, a 6" f/8 Dobsonian isn't so "rich field," but is still a
Dobsonian, so this is more a kind of frequent association than a
set characteristic.

Anyway, it is interesting to examine these usages and get different
people's takes on the "Dobsonian" concept.

Most appreciatively,

Margo Schulter

Lat. 38.566 Long. -121.430

canopus56 wrote:

Newts can be removed from their alt-az boxes and converted for
mounting on a GEM.

Well, with some Dobs, this may be possible, but not with the larger
"sling" mirror cell units like the Obsessions. These cells are designed
only to work in the altazimuth configuration, as they use gravity to
hold the mirror down in the sling. To convert one to equatorial use
would require an entirely new mirror cell that is capable of supporting
the mirror from all sides regardless of its orientation. Clear skies to
you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 14th Annual NEBRASKA STAR PARTY *
* July 15th-20th, 2007, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

On 12 Sep 2007 20:46:38 GMT, Margo Schulter
wrote:

Anyway, it is interesting to examine these usages and get different
people's takes on the "Dobsonian" concept.

Altaz mounts, including simple ones, were around long before Dobson. As,
of course, were Newts of all sorts.

To me, a Dobsonian is:

1) a Newtonian telescope made from inexpensive materials;
2) a simple altaz mount utilizing passive bearing surfaces;
3) a design philosophy based around simple and inexpensive to construct.

Hence, in my view, once you motorize the mount it is no longer a Dob.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

"Margo Schulter" wrote in message
...
Brian Tung wrote:
David Knisely wrote:
Actually, the word "Dobsonian" has evolved over time and has never
really been formally defined.

Yup--and is a point of some contention with folks. Going by what people
actually seem to mean when they use the term, rather than what people
think it ought to mean, it's a Newtonian on a rocker-box altazimuth
mount that rests on the ground (or possibly on a platform). Other
optical tubes seem to be said to be on a Dobsonian-style mount, or (as
you say) simply an altazimuth mount.

Hi, Brian and David.

Maybe there's a variety of usages here also found in other areas. For
example, to most people, a "bulldozer" means the whole vehicle, both the
tractor and the bulldozer attachment. To someone in the trade, however,
it would be more precise to speak of a "tractor-bulldozer," with the
term "bulldozer" properly referring to the attachment.

Similarly, the term "Dobsonian" might more properly refer to the mount,
typically used for a Newtonian but possibly for some other kind of OTA.
However, like "bulldozer," Dobsonian has come often to mean the whole
telescope, including a specifically Newtonian OTA plus the mount.

Dobson himself prefers "sidewalk telescope," which presumably relates
to mount and OTA together -- so that if people thought, "Dobson's
sidewalk telescope," and from there "Dobsonian telescope," then using
the term for the whole telescope as well as the mount would seem
logical.

The other side, of course, is that it's the mount that's more
_distinctively_ "Dobsonian," since Newtonian reflectors had a rather
long history before Dobson championed the design that bears his name.

An interesting question is whether "Dobsonian" has any connotations
that attach to the type of Newtonian OTA involved -- that is, things
not inherent in the definition, but often suggested by it.

One thing I'd suspect people often associate with a "Dobsonian" is
relatively fast optics, or a rich-field telescope, say f/7 or faster.
Maybe this was especially characteristic of the large Dobsonians
that became practical in the first decades of the design on the
amateur market (e.g. Coulter, discussed in another thread). Of
course, a 6" f/8 Dobsonian isn't so "rich field," but is still a
Dobsonian, so this is more a kind of frequent association than a
set characteristic.

Anyway, it is interesting to examine these usages and get different
people's takes on the "Dobsonian" concept.

Most appreciatively,

Margo Schulter

Lat. 38.566 Long. -121.430

Today's "Dobsonian" telescopes have EVOLVED into relatively short focal
length instruments. But most of the originals were far from Rich Field,
short focal ratio scopes... Even in large aperture Newtonians, f/8 was not
an unusual focal ratio in the dim times...

But improvements in mirror making and mirror mounting, have resulted in
evolving mount designs that have drifted toward shorter and shorter focal
ratios to allow more and more aperture in smaller and smaller packages,
without sacrificing structural rigidity or operational smoothness, without
backlash, in both axes... In some respects, the newer scopes are better,
but in some cases they are not. Yet, most of them ARE different, while
sharing some common basics...

Personally, I think we spend WAY too much time worrying about the minute
details of what to call them and why. It's a design many folks have found
to be very useful, and many of THOSE folks have found things they can do to
make it work for THEM, even better. That's evolution... The fact that it's
based on the mechanics of old cannons just further emphasizes the evolution
of the design...

Not to worry... We'll likely still be calling scopes of this basic design
Dobsonians long after most folks have ANY idea where the name came from...

--
Jan Owen

To reach me directly, remove the Z, if one appears in my e-mail address...
Latitude: 33.6
Longitude: -112.3
http://community.webshots.com/user/janowen21