Posts Made By: John Biretta

My favorite among these are the Ultimas. Very nice
coatings (high contrast). Eyecups and eye position
are also very comfortable for binoviewing. I've
used the 30mm, 18mm, and 12mm and recommend them
highly.

TV Plossls are also good. Nice coatings. But I
personally don't care for them in a binoviewer.
The 32mm has this very wide 2" eyecup, and I can
barely get my nose between two of them. The 20mm
is OK. The eye position on the 15mm I find
uncomfortable -- I feel like I'm trying to jam
my eye down into the deep rubber eyecup to see the
entire field. I think they are good for mono-
viewing, but ergonomics are poor for bino.

Meade. I've not tried these in a bino. I used one
or two of them, decided I just didn't like the
coatings, and sold them all. While the Meades
are "multicoated," they seem to reflect alot of light.
They probably used the cheapest 2 or 3 layer
coating thay could produce with a green coloration.

I think this question can't really be answered without
knowing more about where you live, and what kind of
observing you do.

For spotting faint galaxies and nebula, the
9.25" is always going to win against a 5" scope.

For planetary detail, the C9.25 will win big
on the best nights and reward you with unbelievable
detail, and the 5" won't even be close. On
really bad nights the 5" will look sharper
and more steady and might even show more detail.

There are 2 relevant problems with the C9.25.

(1) It is 9.25" in aperture. Nights where the
air is steady enough to make best use of that
aperture for planets are going to be rare, unless
you live somewhere like Florida. This would apply
to any scope of that size or larger.

(2) It is a closed SCT, which means its going to
take a while to cool. Mine sometimes takes
a couple hours to fully stabilize. A plain-old
open tube Newt will cool maybe 2 - 3 times faster.
In this sense, the C9.25 has some disadvantage,
though after-market accessory fans can be added
to help.

I've tried both the C9.25 and MN-76 (Mak-Newt).
I see more detail in the C9.25 on Jupiter,
in spite of the larger CO. C9.25 is also much more
friendly for binoviewing due to huge available
back-focus. Both have cool-down problems to some
degree; available fans help. Dewing is more of
an issue with the C9.25; hard to keep big thin
corrector plate warm. The MN-76 is a huge scope;
C9.25 is much more managable in size. Tough call.

Pin cushion distortion just means the stars are in
slightly wrong places in the view. Doesn't hurt a
thing. You may notice something slightly odd if
you move the scope fast while looking in it -- stars
near the edges will move on curved lines; no
big deal. And if you like looking at fence posts
during the daytime, you'll probably notice it, too.

Some random comments:

I personally found the "purple haze" while viewing
Jupiter in the 6" F8 Synta to be very distracting.
Some people say they can see past it, but I had trouble
doing this.

My experience with Chromacor has been fairly positive.
The purple haze is 90% - 95% gone. Details I see
on planets are virtually the same as with a 6" true
APO scope, so it does work quite well.

At least for me, Jupiter looks much, much better
with the Chromacor. I think differences on Saturn and
Mars are much less, since they don't have much purple
(or blue) to begin with.

I find that the cool-down time on an SCT is a
real limiting factor here in the mid-Atlantic
region. Mine sometimes takes a couple hours to
put out great images, whereas with the 6" refractor
its more like 1/2 hour. So if you like looking
at planets, the SCT may have some issues.

The best planetary views I've ever seen were with
an 11" Newtonian with a mirror by Carl Zambuto.
But a scope in this class is going to cost alot more
than a 6" achromat + Chromacor, and probably have a
long wait-list, too.

Couple quick comments:

I had my StarMaster ELT 11 F/5.4 down at WSP last
month. Now I might be biased, but the detail I was
seeing on Jupiter and Io equaled or bettered any scope
there including the $40K 10" APO. The equatorial band
on Io was plain as day. It cools fast and has
fantastic optics. I use a Tom O. Equatorial
Platform and tracking is great. Only down side I've
found on this scope, is that the collimation has a
slight dependence on elevation (the 4-pole truss has
a tiny bit of sag). But if you collimate at 70 or 90
degree elevation it should be fine. Heaviest part is
something like 30 pounds; in fact it is not too hard
to pickup the entire assembled OTA and drop in on the
rocker box.

I don't have experience with the C11, but can say a
few words about the C9.25 and C14.

I've also got a C9.25 and the excellent reputation
these have is well deserved. The optics are 1/10
p-v range, but it can take hours to cool some nights.
A C9.25 on a G11 is a really nice professional grade
set up.

I also got a look through a couple C14s at WSP and
I will say they were certainly the most bang-for-buck
10" scopes I saw there. Planetary views compared
very favorably to the 10" APO. But I would not have
given them high marks as 14" scopes; there was
either alot of spherical aberration, or there was
color from the 0.63x corrector. Views were great
but extra-focal star test was not pretty.

Good luck!

There are two possible sources of aberration in fast
scopes (F5 or less). It is probably useful to mention
both.

One is eyepiece aberrations -- notably
astigmatism near the field edges -- which you will
see especially in non-premium widefield eyepieces
like Erfles, TeleVue Wide-Fields, and Meade Super
Wide Angles, etc. Stars will be blurry or elongated
near the field edges. Premium eyepieces like TeleVue
Panoptic, Nagler, Meade Ultra-Wide will show only
slight amounts of this aberration.

Then there is actual coma from the main optics.
This will be seen even in the premium eyepieces,
and causes stars near the edges to look like
little cones or seagulls. A coma corrector
will fix this. As Rod says, I think TeleVue is
the only one who made a 1.25" Coma Corrector.
Its like a Barlow, and usually has a 2-element lens
in the bottom. I think it has been discontinued,
but they sometimes appear on astromart. Two-inch
coma correctors are still readily available.

My suggestion is to borrow a couple high-end
eyepieces (i.e. Naglers) and verify that indeed
you are seeing coma in the main optics. And
then get a 1.25" corrector, or possibly consider
switching to a 2" focusser and a 2" coma
corrector, if it really is coma.

If you do decide to get a coma corrector -- one
thing to check is the amount of "in travel"
you have available on the focusser. Most of these
coma correctors need at least 1/2" of inward travel
in the focusser to reach focus. Put your
favorite eyepiece in the scope, focus, and
then see if you have at least 1/2" of travel
left running the focusser into the scope.
If you don't have the 1/2" of travel, you may
have problems reaching focus with the coma
corrector in place.

Good luck!

I've also been very happy with mine. Like Mark, I
usually set up a table in the "camping" section
and keep my eyepieces, junk, etc. in there.
I've used it with an MN-76 + extended dewcap, and
its fine but starts to get a bit tight in some positions
due to 5' long OTA. SCTs or Cass scopes shouldn't
have any problems, though.

I use a JMI NGFS and am very happy with it. Its an
electrically controlled 2" Crayford. See

http://www.jimsmobile.com/sct_accessories_diagram.htm#Diagram

I've used about a dozen of these, and don't
know anything about coating problems; its the
first I've heard of this. A couple yers ago
I heard something about the short focal lengths
(5, 6, 7mm) having an issue with internal
dust, but I can't confirm that either. In my
experience they are flawless and truly superb
eyepieces.