Celestron Omni 127 Review
Some years ago, I lived in a rural location under relatively
dark (mag 5.5) skies.
At the time, I owned an Orion XT10 Dobsonian, and the views through it
Unfortunately, the tube was very heavy and awkward, which made me
reluctant to move
it any farther than out into the yard and back again. (I'm a 5' 6"
active woman, but definitely not an athlete.) When I took a new job, I
house and moved to a new state in a location much closer to a large
city. I decided
that the XT10 would see relatively little use there and reluctantly
sold it, replacing
it with a much more portable Orion Short Tube 80.
After yet another move to the Boston, MA south shore suburbs,
a mild case of
aperture fever set in. I knew that I didn't want to go back to the days
a large Dob around, no matter how impressive the views might be. But
conditions at my third-floor apartment balcony were adequate for good
planetary views, and the observing field of the South Shore Astronomy
skies around mag 5, despite issues with high humidity.
I agonized between the Orion Skyview Pro 127mm
Maksutov-Cassegrain for $699 and the
Celestron Omni XLT 127 Schmidt-Cassegrain for $629. In the end, the
collimation, lighter weight, and greater versatility of the Omni 127
It was frustrating not being able to find much in the way of reviews on
the Omni 127,
and I hope that the review you are now reading will help remedy that
The telescope and mount were ordered from Adorama Camera,
given its good reputation,
relatively nearby location, and free shipping. Although 7-10 day
shipping was chosen,
the order was placed Wednesday night and the scope was on my doorstep
when I arrived
home from work on Friday. (After several good clear nights of lunar
with the ST80, it was raining for the first time in days when the Omni
Telescope Arrival and Assembly
The scope and mount were well packaged. All parts were
double-boxed and some small
items were triple-boxed. Although there was very minor damage to the
there was no damage at all to the inner boxes, scope, OTA, or
The CG-4 Mount
After using an EQ-1 equatorial mount to support the ST80 for
several years, the
CG-4 is a revelation. Now, the EQ-1 is by no means a bad mount. It's
to be inexpensive, lightweight, and highly portable and serves that
It is adequate for supporting a lightweight scope such as the ST80. But
time is very poor, making high-power focusing a tedious guessing game.
The CG-4 is a much heavier mount, but it is still highly
portable. I have no
trouble picking up the entire mount/OTA assembly in one piece and
moving it across
a room, although I doubt that I will carry it through doors or down
stairs that way.
There is scarcely any plastic anywhere in the mount; only the slow
dovetail locking knobs, and setting circles are plastic. Even the
handles are metal. I am confident that this mount could handle an OTA
heavier than a C5.
Although the mount shipped with two counterweights, only the lighter 4
was needed to balance the small 6 lb OTA. Acceptable balance is easy to
The instructions are clear, and include pictures showing the names of
and drawing lines to the named component. This is very helpful when the
tell you to remove or tighten a particular know or bolt; you know
which one is being discussed.
Slow motions are very smooth. Those who complain of the Synta
would be very happy with the CG-4 lubrication as shipped. There is a
of backlash in the slow motions, but it does not interfere with star
hopping at all.
Above 200X, the slow motions are no longer very slow, and a gentle hand
The C5 Optical Tube Assembly
Fundamentally, the Omni 127 is the latest incarnation of the
The lightweight OTA is incredible. Not having any prior experience with
SCT's (although I have looked through those belonging to others at star
I didn't realize just how easy it would be to carry around the bare 6
lb OTA. It's
only marginally heavier than the 3.8 lb ST80. I wish that Celestron
would make a
custom case available for the OTA; I would gladly pay extra for one.
include one with the C5 spotter scope, which is essentially the same
must already have designed and manufactured the case. Why not sell it
to Omni 127 owners and have an additional profitable item?
I was somewhat disappointed that the scope shipped with a 6x30
inverting finder, which is not adequate for my light-polluted skies. So
same time the Omni was ordered, a 9x50 right-angled correct-image
ordered from Orion. If you live in suburbia or, worse, an urban
on purchasing a 9x50 finder separately. (I absolutely love this finder
recommend it highly.) The standard dovetail on Orion finders fits
the finder dovetail slot on the Omni, so installation is trivial.
It is not easy to sight down the finder or primary optical
tube to get things
pointed in the right general direction. If you are used to long, slow
or Newtonians, this may require some adjustment on your part. After
star-hop with the right-angled 9x50 finder, I ordered a Rigel Quik
made a big difference in my ability to locate objects.
The focuser moves very smoothly, with just enough friction to
remain in place.
The only planet in the sky at present is Jupiter. I have
looked at it many
times with the ST80 using powers anywhere from 25X to 133X. But the
power and violet haze overwhelm the view and show little but the main
belts and Galilean satellites.
First light in the C5 was on a very hazy, overcast night with
only a few objects
showing. I was able to view Jupiter at 208x as a quick test, but the
image was quite soft and fuzzy, with no way to separate the effect of
from any miscollimation or the natural diffraction fuzz of the large
A few nights later the seeing and transparency improved. I was
able to set up
the ST80 and C5 side by side and compare the views of Jupiter.
chosen to yield approximately 78x. The planet looked quite similar in
but there was substantial chromatic aberration seen in the ST80 and
none in the
C5. There may have been marginally more detail visible in the C5, but
was quite subtle. Moving up to 139x softened the view substantially,
says more about our hazy, blurry New England nights than about the
It does appear that the C5 arrived slightly out of collimation.
Arcturus at moderately high power yielded very clean, concentrenic Airy
and rings. However, 2nd magnitude stars just barely out of focus showed
rings are not *quite* perfectly concentric. I made a crude artificial
and tweaked collimation slightly. Rotating one secondary screw about
a turn is all it took, so it clearly wasn't too far off as shipped.
Any new observers thinking about buying the Omni 127 (or any
other SCT) need to
realize that the scope MUST be properly collimated to see its
potential. If you
aren't certain how to do it, seek help from your local astronomy club.
It is not
a difficult process, and it is critically important.
My eyepiece assembly is very modest, including only
inexpensive 1.25" eyepieces.
I hoped that the slow (f/10) focal ratio of the C5 would not tax them
as faster wide-field scopes do, although in practice they have
well in the ST80 (f/5). My set includes a 32mm Orion Highlight Plossl,
and 10mm Sirius Plossls that came with the ST80, a University Optics
and 9mm, 7mm, and 6mm University Optics Abbe Orthoscopics. The 1250mm
of the C5 is identical to that of the XT10 I once owned, so the
purchased for it are also a good fit for the C5. An Orion Shorty Barlow
With Sagittarius well-placed from my balcony, I turned the
scope on M22. Despite
local light pollution, I was able to see both guide stars and the
in the 9x50 finder. (Although I was able to find the globular in the
was invisible in the 6x30 finder.) At 78x in the C5, it was clearly
unresolved. At 139x, it began to resolve into stars around the edges.
It was quite
an attractive sight, and would no doubt have been more more so under a
The CG-4's slow motions and rock-steadiness make star hopping
M28 was easily found at 78x.
I am a fairly serious lunar observer with a shelf full of
lunar atlases (both Rukl
and Hatfield), the complete set of Clementine Lunar Digital Image
Mosaic (LDIM) CD's,
Patrick Moore's "New Guide to the Moon", Charles Wood's
"The Modern Moon: A Personal View", etc, etc. It was the limitations of
ST80 for lunar observing that really pushed me into purchasing a larger
with more resolving power and no significant chromatic aberration. The
ordered the new scope, the ST80 had failed to show any sign of the
Humorum rilles at 133x, despite good seeing and near-optimum terminator
So how would the C5 stack up?
I had owned the new SCT for several weeks before getting
and a Moon in position to be viewed from the balcony. Mediocre seeing
image boiling at 208X (6mm Ortho), but the amount of detail visible was
Dropping to 139X (9mm Ortho) improved the image steadiness while
of the detail. The Alpine Valley was prominent, with shadows bring the
into good relief. Cassini was quite impressive, and the terminator fell
west of the famous Ptolemaeus/Alphonsus/Arzachel group. Wrinkle ridges
on Imbrium. The difference in resolving power vs. the ST80, even at the
magnification, is very evident. If you are seriously interested in
detail on the lunar surface, I recommend against small aperture scopes
(i.e, 80mm or less). There's much more to see at 4 - 5".
A modest 8" Dob may still be in my future, opening up the DSO window a
wider and giving better views of globular clusters. However, since I am
often seeing-limited, I am not sure that more aperture will
improve planetary views here on 90% of observing nights. Hopefully we
will be in
a position to buy a house next year, which will help with storage and
carry-out and setup. But the C5 will continue to have a role as my
equatorially-mounted mid-sized scope even if a Dob joins the chorus.