Re: Orion StarMax 102mm EQ or AstroView 120mm EQ?
From: Stephen Paul (spaul219_at_hotmail.com)
Date: 03/28/05
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Date: Mon, 28 Mar 2005 14:52:57 -0500
"FiremanE42000" <Seth_Kolasinski@cox.net> wrote in message
news:qvW1e.86942$755.14597@lakeread05...
> I'm looking to purchase my first scope and I'm between the Orion StarMaxT
> 102mm EQ Compact "Mak" and the Orion AstroViewT 120mm EQ Refractor. Has
> anyone used either one or can anyone give me an idea as to which one might
> be best? Thanks
These scopes are pretty much in different categories as far as use is
concerned.
The 102mm F13 Mak is a small instrument with a long focal length (around
1300mm).
The 120mm F8.3 refractor is a larger instrument with a shorter focal length
(around 990mm).
One way to look at it is that the Mak is basically a replacement for a 102mm
F13 achromat refractor (although it isn't quite that simple, and the 102mm
F13 achromat will certainly outperform the 102mm Mak for lots of reasons, as
discussed below).
With that in mind, the question you might really need answered is, which is
better, a 120mm F8 refractor, or a 102mm F13 refractor?
The answer would be that the 120mm F8 will be better on deep sky objects
like nebula, open clusters, globular clusters and galaxies, where low powers
are most useful. However, due to the relatively short focal length in its
refractive elements (primary lens), it will have quite a bit of "error" in
bringing all colors to focus at the same point at high power. It will
therefore be a somewhat poor performer on planets, which demand high power
to bring out details at larger image scales.
A 102mm F13 refractor will be good on planets, but lacks the light grasp
(apeprture) to make deep sky images appear as bright as they will in the
120mm.
This would also hold true for the 102mm Mak, if it performed as well, which
it will likely not. The rule of thumb for a Mak is it should have equivilant
performance to a well color corrected refractor equal in size to the
aperture of the Mak, minus the "central obstruction" of the Mak's secondary
mirror (the dot on the front lens). This obstruction might be as large as
30% by diameter (30mm), reducing the performance to that of a well color
corrected 70mm refractor.
Bottom line? If you are dead set on one of these two scopes, for whatever
your motivation (it's not price alone is it?), then the 120mm would be
"better" for deep sky, and the 102mm would be better for planets, and double
stars (and portability).
For the price of the Mak, you could possibly get a scope that is more
capable in raw optical performance. Like a 6" Dobsonian. The 6" F8 Dobsonian
is virtually without color error, has a lot more light grasp, and is quite
easy to manage. The only real negative of the Dobsonian, is the lack of a
clock drive, which means you need to nudge it along to keep an object in the
eyepiece. It's kind of a pain, but you will see better what you are looking
at, for the same money.
Given that low power views are most often what are used for deep sky (half
degree to 1 degree field of view), you get lots of time between "nudges", so
it is only when planet observing (1/4th degree field of view is not
uncommon) that the Dobsonian is at it's worst.
Good luck,
Stephen
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