Re: C8 vs. C9.25
- From: "Mij Adyaw" <mij@xxxxxxxxxxxxxxxx>
- Date: Tue, 19 Dec 2006 08:52:16 -0800
I have heard that the C9.25 is optically better than the Meade 10 inch. I
have never owned a Meade 10 inch, but currently own a C9.25 and it is
optically very good.
"Mike" <mike@xxxxxxxxx> wrote in message
news:0yUhh.90407$rv4.84463@xxxxxxxxxxx
Excellent point of view. I think a Meade 10" is a nice mid-range way to
go.
"AstroApp" <AstroApp@xxxxxxxxxxx> wrote in message
news:fqsdo2583nub77l1c4s6k6fs21a697vnd3@xxxxxxxxxx
On 17 Dec 2006 10:24:46 -0800, "Rich" <rander3127@xxxxxxxxx> wrote:
Mike wrote:
Is there a significant difference between these two?
The price is hundreds of dollars different and you need
a heavy duty mount for the 9.25. How much more
viewing would the 9.25 give you over the C8?
Depending on where you live, it could make a significant difference.
Extra aperture is always better. You might be straining to see stars in
a global
cluster in the C8 and easily see them in the 9.25."
I wonder if I can possibly agree with the last statement. There is
not a huge difference WRT to resolution and light gathering compared
to the relationship between an 8 and a 10 or 11 inch scope.
Generally using the accepted formulae for comparison, one comes up
with some fairly reasonable numbers:
8 inch:
light gathering 843 times the human eye
Dawes limit 0.57 arcseconds
Stellar magnitude limit: averages around 13.5
9.25 inch:
light gathering 1127x
Dawes limit 0.49 arcseconds
Stellar magnitude limit: perhaps around 13.8
You can go deeper in stellar magnitude limit by removing the star
diagonal, adjusting the magnification, and if your own experience in
detecting stars might be better than average; my experience tends to
suggest that it is possible that an 8" SCT with critically sharp,
focused optics COULD reach (under absolutely breathtakingly perfect
seeing, with clean, ultra-coated, brand new optics, by a fairly young
observer with exquisite eyesight) about 15th magnitude; with the same
criteria a 9.25 inch SCT could perhaps reach 15.4: this is by using
the best limiting magnitude calculator I know of, which is here:
http://www.go.ednet.ns.ca/~larry/astro/maglimit.html
Now in both cases, the difference in stellar magnitude limit is either
0.3, or 0.4. That would mean that some of the fainter outlying stars
in the brighter, large diameter globulars would not always be
detectable in the 8 while they WERE just barely visible in the 9.25,
everything else being equal. The resolution difference is not huge so
the ultimate difference of discerning individual stars won't be nearly
as great between the 8 and the 9.25 as when comparing an 8 to a 10 or
11 or 12.
Then, there's the issue of the central obstruction and whether we're
comparing f/10 to f/10, or f/6 to f/10 Schmidt Cassegrains, etc etc.
However, IMO based on comparing my 8, 10, and 11 inch scopes, I wonder
if it is a quantifiable statement we'd all agree on that, quoting you,
"You might be straining to see stars in a global [sic] cluster in the
C8 and easily see them in the 9.25."
Generally, one is almost always "straining" to see the stars of
globular clusters as individual stellar points in an 8" scope,
especially a reflector (it's easier in say a 7" APO refractor, or
sometimes even in a *6* inch APO...) Aside from, say, M3, M5, or M13,
and maybe M22 if it's up high enough, the resolution of 8 or 9.25"
scopes and their light gathering and limiting magnitude are really not
optimal for "going inside" a globular cluster; larger scopes are much
better.
See this page for a comparison (I agree with the depictions here based
on experience with various scopes I've owned and used):
http://www.obsessiontelescopes.com/m13/index.html
The only caveat here is the in order for the fainter stars to show up
in a fairly good brightness relation with the stars shown by the
larger apertures, the brightness is scaled so that you CAN see a
difference: but it's not the REAL difference since the screen of your
typical monitor cannot produce the luminance of the large scopes nor
the true dynamic range; and the monitor's background raster is
brighter than the visual background in an eyepiece, in a very dark
sky.
It's often next to impossible to do a good, accurate comparison even
at a star party with representative scopes available, but in lieu of
that, I'd suggest doing a little observing, if possible, with an 8 and
a 9.25 over time, to get a concept of a "baseline". I've done that
and in my opinion, a 9.25 is not a "huge leap" above an 8, all things
being equal. The brightness and resolution improvement do not knock
your socks off. Even in my 11, globulars don't do that. But on a 17
inch scope: they DO.
AstroApp
.
- References:
- C8 vs. C9.25
- From: Mike
- Re: C8 vs. C9.25
- From: Rich
- Re: C8 vs. C9.25
- From: AstroApp
- Re: C8 vs. C9.25
- From: Mike
- C8 vs. C9.25
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