Minimum aperture for globulars and galaxies

Bill Meyers wrote in message ...

What in your opinion or experience is the minimum aperture necessary
for satisfying views of globular clusters and galaxies?


Assuming these "satisfying views" are permitted to be on a screen
(after stacking and processing multiple CCD frames taken through
various filters), then 40mm (or even less) would probably do.

Not the point of the question, right? I'll be less flippant :-)

I've an 80mm ED piggybacked on a 10" SCT. When "doing visual", I've
begun to use both scopes as it's usually just a turn of the head to
switch from one to the other and compare the views.

The verdict? Both are satisfying! The SCT for the extra resolving
power and reach down to dimmer stars. The ED for the brighter, wider
field of view that puts the object in context.

Personally, I'd say this applies to globulars more tha galaxies
though. Since moving into CCD imaging, I can't get quite the same
satisfaction from a dim smudge in the eyepiece. So I guess a couple of
metres of aperture might (just) satisfy me in that regard :-)

Cheers
Beats

Bill Meyers wrote in
:

Hello, all,
What in your opinion or experience is the minimum aperture
necessary
for satisfying views of globular clusters and galaxies?

Basically about 2" more aperture than whatever you have now. g

10" f/6-7 newt. One of Rolands 6" apo's would suffice ina pinch ...


Bill Meyers wrote:

Hello, all,
What in your opinion or experience is the minimum aperture necessary
for satisfying views of globular clusters and galaxies?
Thanks,
Bill Meyers

Hello, all,
What in your opinion or experience is the minimum aperture necessary
for satisfying views of globular clusters and galaxies?
Thanks,
Bill Meyers

Globs: Pretty nice in an 8 or 10 incher. Brighter ones resolve reasonably
well.
Galaxies: I think Paul's "2 inches more than you have" is a good answer. I
spent the last 2 weeks out on the Navajo Reservation in NE Arizona. Some pretty
dark skies, 7300 ft altitude, 10 inch Newt. Looking for Stephen's Quintet, I
was thinking my 12.5 incher would have been better...

jon

"Bill Meyers" wrote in message
...
Hello, all,
What in your opinion or experience is the minimum aperture necessary for
satisfying views of globular clusters and galaxies?

I've settled for a 100mm F5 achromat on an ultra-light altazimuth mount, as
a compromise between aperture and portability.

Thanks to all for your responses. I'll reply at this time but hope to
hear from more people. Here are my thoughts based on your responses so
far. It may take several posts to do this since there is a lot of
information in the replies.

The basic law of survey research is, pretest your questions on a small
group before using the questions on a larger group. This was not
possible in this context, with predictable result that the phrasing of
my question could have been improved on. It us now clear that what I
should have asked was something like, "In your personal experience,
with the kinds of globulars and galaxies you usually observe ,from the
kinds of skies you usually observe from, what do you find is the minimum
aperture that gives you satisfying results on globular clusters and
galaxies? You may answer separately for globular clusters and galaxies,
if you wish."

I posted my query on the yahoo talking telescopes group and on the
Astromart equipment forum, so there are responses from a broad range of
people.

I had also checked into three classic books on observing from the days
when small refractors were about all thatwere available, that is before
the six inch reflector, equatorial mounted was being widely built by
amateurs, and before reflectors became easily commercially available,
and of course long before the era of SCTs and Dobs.
William Tyler Olcott, in the 1909 "In Starland with a Three Inch
Telescope" says of M13 "is well worth observing... It takes a 4-inch
glass to catch the twinkling of the stars." Olcott and Mayall in Field
Book of the Skies" (1929, 1954) say "It is easily discernible in an
opera glass but it takes a 4-inch telescope to resolve its stars."
Bernhard, Bennett and Rice, in "New Handbook of the Heavens" (1941,
1948) say of M13: "The outer stars are resolved in a small telescope
and with a larger glass the entrancing beauty of the great globe of
stars is revealed."

So much for the classic view before the advent of modern amateur telescopes.

The responses I received to my posting were rich and complex. See Part 2
Ciao,
Bill Meyers

Hello again,
As a quick summary, for galaxies, people mostly said, the larger the
better. There was a view that for detail in the structure of galaxies,
that is, dust lanes, mottling, spiral structure, rather than only
orientation and shape, one needs 12 inches and preferably considerably
more. For a satisfying view, many people wanted to see detail in the
structure, hence a large telescope. Others found satisfaction in simply
seeing the galaxy, so answers in the realm of 70 mm binoculars, or a
four inch telescope, were given.

Generally speaking the apertures suggested for minimum satisfying views
of galaxies were considerably larger, say four or more inches larger,
than those suggested for minimum satisfying views of globular clusters.

I suspect that some people's answers on galaxies were influenced by
their views through their own large telescope or the large telescopes of
observing companions. Once you have seen structure in say NGC 4565
through a large telescope, it may be harder to experience merely
discerning the galaxy in a small telescope, as satisfying. There may be
an "adaptation level phenomenon" here, in that what you find as
satisfactory is based partly on what you have already experienced.

Next time: more on globulars.

Ciao,
Bill Meyers

Hello once more,
The question as it applied to globulars was hard or impossible for some
people to answer. They pointed out that it depends on the darkness of
the sky you are observing from, and the particular globular you mean,
and how you define "satisfying."
clearly a very much larger aperture is required to resolve distant
Palomar globular clusters than is required for Omega Centauri.
People who observe from the southern hemisphere sometimes pointed out
that for Omega Centauri, 47 Toucanae, and one or two others, very small
telescopes or large binoculars will resolve them in a satisfying way.
But other southern observers said the sky, with regard to globulars and
galaxies, opens up at 10 inches of aperture.
Overall, the most frequent responses were 8 inches of aperture or 10
inches of aperture, or 8-to-10 inches of aperture.
Some users of SCTs or large apos, said 8 inches. Others said in effect,
satisfying globular viewing starts at 8 inches (with the implication
that it improves markedly after that).
Some apo users said 6 inches because of the pinpoint star images given
by an apo. In general, apo users suggested a smaller minimum aperture as
satisfying.
Noteworthy was the fact that a number of people found that the
improvement in globular cluster viewing as one goes from 8 to 10 inches
in aperture is much greater than one would expect.
It was clear that improvement in viewing of globulars continued as one
went to 12 inches of aperture and larger. Some felt 10 inches of
aperture was very satisfactory, and others felt more comfortable at 12.
Very large aperture for globulars, well over 12 inches, tended to give
even better views; there was no law of diminishing returns with
increases of aperture as far as globular are concerned, according to
respondents.
Some respondents found viewing a hazy granular globe of stars against a
sky background very satisfying in itself, and suggested apertures as
small as 80 mm.
I also noticed how much better Southern Hemisphere observers have it.
You can get a fuller picture of our observers's experiences by viewing
the SAA, Yahoo talking telescopes, and Astromart equipment forum
threads. Each has a variety of observers, and some very accomplished
observers or people highly knowledgeable about telescopes. Different
sorts of people post to each, but overall I would say there is consensus
among the three sources.
I think the responses have considerable implications for what sort and
aperture of telescope one feels comfortable recommending to beginning
observers. We may be more able to clearly express to them what to expect
from a given telescope, and avoid disappointments.
Many thanks to one and all for posting your views and experiences. I
hope the results will be helpful to others.
Ciao,
Bill Meyers

On Thu, 23 Sep 2004 20:06:53 -0400, Bill Meyers
wrote:

Hello, all,
What in your opinion or experience is the minimum aperture necessary
for satisfying views of globular clusters and galaxies?
Thanks,
Bill Meyers


10" under suburban skies.
6" under dark skies.

Anything below that just starts to reveal stars
(in globulars) and some detail in galaxies.

On Thu, 23 Sep 2004 20:06:53 -0400, Bill Meyers
wrote:

What in your opinion or experience is the minimum aperture necessary
for satisfying views of globular clusters and galaxies?

Hmm . . . you did specify *minimum* didn't you? When asked in that
manner my reply would be:

The smallest telescope I happen to own -- 80mm. I find satisfaction
in finding and identifying objects with small telescopes. Any visible
details that might greet me from within an object would be looked upon
as 'icing on the cake'.

As long as a person doesn't have unrealistic expectations for what
they ought to see with a given instrument they ought to be able to
find the views satisfying. It shouldn't matter if they're using 8x42
binoculars or a major observatory telescope.

Sketcher
To sketch is to see.