30", 18", 12", 10", 8", 80mm, GOTO, go home it's 3am!

Some recent impressions and mutterings...

First a very brief side by side of the 12, 10 and 8 inch versions of
the Guan Sheng dobsonian. The 8 is mine, and the other two belong to
members of my club. We were observing under mag 5.5+ skies with below
average transparency and seeing.

The bad news is, more _is_ more. This is expected of course, and
something I'm familiar with. What I found interesting here was the
nature of "more" in this incremental comparison of apples with apples.

1. Eta carina in the 8 inch was nice, but in the 12 I was surprised
that it was not only brighter, but showed noticeably more detail and
structure. I started to see depth in the nebulosity which allowed
extended exploration of the object, in a way that the 8 did not.

2. The Tarantula nebula in the 10 was very nice, but its owner in
comparing with the 12 noted the ability of the 12 to resolve the loops
of gas.

3. Omega centauri in my 8 is resolved and rewarding, however the 12
was brighter, more engaging, and started to differentiate the brighter
stars in the cluster. It hinted at the kind of view I've seen in an 18
inch. The rule of thumb regarding amateur telescopes made sense he
8 inches is the largest small scope, 12 inches is the smallest large
scope.

4. The Jewel Box open cluster, and southern sky staple, was
(thankfully) not significantly better in the 12, at least at a quick
glance.

5. Jupiter was up but wobbly, much of the time so much so that even
the 80mm was on a par.

Speaking of the 80mm, it was an evaluation sample of the Orion ED?
refractor (f7.5). Very nice. In fact I found its presence amusing:
here I was grudgingly admitting the increase in observing pleasure
provided by 2100 cm2 of effective aperture over 940, and at the same
time 200 cm2 was being taken seriously! But serious it was, with
pleasantly low false colour, good contrast and resolution across the
field, and…_portability_. The experience of travelling and finding
yourself under clear dark skies brings home the lesson that aperture
wins - small aperture that is. 80mm in the car is worth 12 inches in
the garage.

The 10 inch is something of an ideal size. Being f/5, it is only a few
inches longer than my 8 inch f/6, although the extra OTA weight (35lbs
vs 20lbs) may make the 8 a more useable option for some. The 12 really
is a serious lump of telescope (OTA 60lbs?), but it rightly belongs in
this comparison I think. At the end of the night, its owner did just
what I did with my 8, threw it in the back of his car in two pieces
and drove home (albeit with rather more effort and car space).
Importantly, it is still shy of the larger truss category where set up
and take down mean considerably more time and fiddle factor.

Perhaps with the 12 inch the improvement over the 8 and 10 is, in some
sense, a Dawes limit resolution "multiplied by" the extra light grasp?
Whatever the case, the 12 inch will take you places the smaller scopes
will not.

There was an ETX125 whirring on the night. A nice scope, but the extra
effort of targeting a larger dob manually seemed generally worth it.
At least for visual observation. At least for low power viewing. At
least for DSOs. At least if you had the patience to look up a chart
and hop to it :-)

Enter C11. Funny how when the night wears on, the manual scope drivers
tend to slacken off and congregate around the larger GOTO scopes.
You're getting tired (it is 2am), and it's a relief to preview on the
laptop, then slew to and _track_ (heaven). Perhaps a quick tour of
minor objects in a constellation, or peek at Neptune and Pluto. You
generally just wouldn't bother in a manual scope by this stage of the
game. And with a C11 there's enough aperture to make it worthwhile.
I'm guessing though that DSCs would help close this gap.

A bit of a sanity check with all this talk of aperture is the fact
that on this night, and on others, a 30 inch dob (with eq platform)
sat unused in a nearby roll-off shed. Or is this insanity, the
confession of a crime?! In practice, there is such a thing as too much
aperture. With this circus canon (f/5 I think), anything over 45
degrees and you need to maneuver and ascend the "stairway to heaven"
viewing platform. Certainly globulars are 3D fireworks in this beast.
Maybe I should just get off my butt and grab the bull by the truss
tubes. When the 18-20 inch dobs are out they do tend to get a good
work out. You're in step ladder territory, but it's nowhere the drama.
A C14 must be a nice combination of convenience and aperture - once
set up anyway.
I wonder if big glass on the decline with growing accessibility of
CCD? Sitting in front a computer screen 5 days a week, I'm very happy
for the moment to catch some photons first hand. With bonus emailed
images in the week following from the CCD guys.

My non-astronomical friends sometimes jokingly ask what's changed up
there. I'm somewhat surprised that after 12 months into this hobby I'm
no less interested. In fact, after a string of cloudy nights I almost
need a fix. And I probably need to get clear of this
compare-and-want-more roundabout for a while and just observe and
enjoy!

Mark

PS Don't leave your binoculars unattended on a extended camera tripod
on a windy night, or they might topple over and snap off the threaded
brass piece the mount adaptor screws into :-(