Re: Getting a bigger telescope (was: Lunatic in Palo Alto ...)

Jeff, I think I am not making myself clear. Let me try
again.

As far as I can tell, what I might see with a telescope
in the 20 to 24 inch range is very much like what I have
already seen -- no new classes of objects become visible.
If so -- and I could be wrong -- then I don't want a
telescope in this aperture range simply because getting
one would in fact constitute standing pat, in that I
would implicitly be accepting that I would just be seeing
more of the same. And I do *not* want to stand pat, that
is the whole point.

There is no argument that even a small aperture increase over
what I have will show more stuff like what I have already seen.
But I would like to see different kinds of things altogether.

I do *not* want to stand pat. How much more aperture do I
need to see objects that are qualitatively different --
different in kind -- from objects that I have already viewed?
A qualitative difference of this kind would be enough to make
me want a larger telescope. (Which is not to say that I could
afford one or would be able to haul it around and set it up,
those are separate issues.)

How much more aperture do I need, to see entirely new *kinds*
of deep-sky objects?

An interesting separate issue is what limits portability,
setup, and use of a telescope in the field. These matters
are at least as much opinion as anything else we have
discussed, and are compounded by the fact that some of the
folks who do custom work, or build for themselves, are
extremely clever. However, even without too much cleverness,
it is clear that quite large telescopes can be made sorta kinda
portable.

For example, there are plenty of vans that will let you load
a four-foot-wide object through the rear doors. Thus, given
a long, strong ramp, due caution, and perhaps a winch, it ought
to be possible to get Dobson components four feet wide and
weighing 500 pounds or more in and out of the back of an
astronomer's van. Even with generous allowances for clearance
and no particular cleverness, it is not hard to imagine a
one-meter-aperture Dobson being van-transportable.

Even at f/3, the eyepiece of such a one-meter is way up there.
Climbing the ladder might be a usability issue for some, though
it might make it more difficult for those mountain lions to get
at your toes.

So let's turn on the cleverness. Or at least let's fake it.

How about a compound design? I keep thinking about a
Dall-Kirkham, which has a less strongly figured primary than
a Newtonian -- ellptical, not paraboloidal -- and a convex
spherical secondary, which makes it much easier to collimate
than most other two-mirror compound systems. Instead of
perforating the primary, let's put a flat even with the
side bearings and reflect the beam from the secondary
out along the altitude axis, to an eyepiece position at
the center of one side bearing. (This configuration is
called a "Nasmyth focus", and has been used occasionally
in large compound reflectors in the past.) You could sit
in a chair at ground level to observe. With an f/3
primary, the overall focal ratio might come out f/10 or
f/12, which would be fine -- that side bearing surely ought
to be able to support the 84 mm Nagler you might want for
viewing faint extended objects. (Seriously, any SCT user
will tell you that deep-sky work at f/10 or so is no trouble
with a big Koenig eyepiece or the like.)

Alas, I am not qualified to build such a beast, and I doubt
I could afford to buy one even if they were commercially
available. And I am still not sure whether a meter of
aperture would let me see new kinds of deep-sky objects.

-- Jay Reynolds Freeman
---------------------
Jay_Reynolds_Freeman@No-Spam
http://web.mac.com/jay_reynolds_freeman (personal web site)

On Jun 28, 2009, at 9:54 PM, Jeff Gortatowsky wrote:

So my mistake:

The way I read many of your posts was:
"Nothing would be 'significantly' better and more (or as) portable
than what I have already have." That we'd agreed to disagree on.

If instead at the core of the matter you are saying, "I've seen
enough. I am happy to stand pat. What I might see with 8 to 10 inches
more of aperture is not worth it to me.", then by all means, lets end
this thread. But lets end it on "I am happy to stand pat." No one can
argue with that.

There are scopes as 'portable' as Harvey and they will show more. It's
all, as you said, in the definition of 'significant'.

Best wishes
Jeff

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