Re: Looking at 130mm reflector . . .
From: Stephen Paul (smarshallpaul_at_gmail.com)
Date: 03/27/05
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Date: Sat, 26 Mar 2005 19:21:20 -0500
jkstum wrote:
> I need some guidance on buying a telescope. I am really ignorant on all
> the telescope specs so I have been doing some reading. Here is what I
> need some help finding out.
The most important parameter to learn and understand when it comes to
telescopes that you will use for observing, is "aperture". The larger
the aperture, the brighter everything appears, and the more "resolved".
For example, a globular cluster that appears fuzzy "ball" of stars in a
100mm aperture, will appear as a fuzzy ball with individual points of
light surrounding the outer regions in a 150mm, or larger aperture (it
will be "more" resolved). The difference between 100mm and 130mm is not
insignificant. However, it appears pretty damn insignificant when you
see the difference between 100mm and 200mm aperture, and then again the
difference between 200mm and 300mm. There's a trend here, a trend where
aperture means everything.
Get the largest aperture you can afford.
For $400 you can often find a used Asian 10" F5 Dobsonian and negotiate
for an eyepiece or two to be thrown in. Most folks end up with a 25mm
and 10mm Plossl eyepiece when they buy one of these scopes new, and
should be willing to include them on the deal. Figure you're going to
pay some shipping costs, so you'll be a bit over the $400 budget unless
you can find one within pickup distance.
An 8" F6 Asian Dobsonian can be found for around that price, new. The
difference between the 8" (200mm) and the 10" (250mm) is also not
insignificant at the eyepiece, but the portability of the 8" is better,
in that it is housed in a 10" diameter tube, rather than a 12" diameter
tube. Those extra 2" of aperture turn into a considerable amount of
extra volume, making the 10" telescope quite a bit larger, even if the
length of the tube is really only a couple inches more.
All that said, a 130mm aperture isn't "too" small either. If you believe
the portability of the 130mm Space Probe better fits your lifestyle,
well, nobody can answer that for you.
I have an 8" (200mm) F4 reflector (one of several scopes) which is very
short and super portable, until you take into account the size of the
GEM you need to support it. A Dobsonian mount is much easier to deal
with, as it is essentially just a box that sits on the ground, into
which you "drop in" the telescope. Aiming is as easy as left and right,
and up and down.
I'm not going to sugar coat it. Finding stuff can be a real bitch with a
Dob (and a GEM), especially at first. But once you master the concepts
of aiming the scope in altitude and azimuth based on a "finder chart",
getting there with a Dob isn't really a bad experience. Oh, it may still
take you some time to find unfamiliar objects, but as you mature as a
Dob user, you learn an entire new level of patience, perseverance, and
reward.
I recommend the 8" Dob as a minimum, and don't look back. I have a 12.5"
mirror set in a structure large enough for a 14" mirror set. The OTA is
oversized for the mirrors I use. I don't care about the size, because I
roll the scope out of the garage on a handtruck. However, when I
traveled with a scope, the 10" F5 Asian Dob fit in the car without much
trouble at all. For a while, the 10 incher was my most used telescope,
now I switch between a 102mm ED F9 refractor, and the 12.5" Dob. The 8"
F4 is possibly a short timer in my inventory, as I purchased it
primarily to experiment with and to learn imaging with a DSLR. I don't
think it's so hot as a visual scope for reasons I won't go into here.
Best wishes in you search. My guess is that your binocular experience is
an indicator that like many of us, you are about to embark on a journey
that includes buying and selling some number of telescopes, in search of
something that is just right for you as you figure out just what it is
that you want out of astronomy. That's something that isn't always clear
up front.
Personally I have _always_ enjoyed being outside at night (as long as
the bug count is relatively low ;-)). For me, recreational astronomy is
just a natural progression of my love of the night sky.
Someone asked here not so long ago how to get kids interested in
astronomy and keep that interest. My answer is to take them camping on a
regular basis, and help them develop a love of the sky and to be
fearless in the dark. Astronomy will follow. It may be years before they
return to rekindle those memories, but they will return.
Stephen Paul
Shirley, MA
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