Omni XLT 150 Review
Celestron's new line of low-cost Chinese import telescopes, the
Omni XLT, has intrigued me since its announcement. The reason is simple, if
slightly ridiculous: the colors. The deep-blue-and-white color combination is
very appealing to me (view my web site for confirmation). Recently I learned
that Astronomics had a slightly used example of one of the cheapest models, the
$400 Omni XLT 150 reflector, available for a total of $338. Since it's easy to
blow more money than that on a single eyepiece, I decided to satisfy both my
curiosity and my liking for blue telescopes and white mounts by ordering it.
The scope arrived promptly in two boxes of substantial size. Both
were double boxed, which was good, since both had suffered at the hands of
FedEx. The inner boxes and their contents were in perfect condition. The larger
and heavier of the two boxes contained the mount and tripod, which are
identical for each of the four Omni XLT models (the others being a 102mm f/10
refractor, a 120mm f/8 refractor, and a 127mm SCT). The other box, considerably
lighter in weight, contained the optical tube, rings, dovetail bar, and
accessories. Everything was packed well and sensibly, and all parts are present.
Since I am a wizened scholar of telescopes and their ways,
nothing in those boxes was a mystery to me. I quickly assembled the telescope
without referring to the manual. For those needing it, the documentation
is comprehensive, well-written, and useful. Also included is a basic version
of "The Sky" planetarium
software, if you happen to use Windows and have nothing better already.
The assembled telescope is very handsome. The tube color is
blueberry, slightly metallic and sparkly. The mount and tube fittings are
finished in a thick, glossy, snow-white paint. I was not disappointed with this
aspect of the telescope.
The main tube is made of thin, rolled steel with a prominent seam
opposite the finder mount. It's out of round along this seam, being a bit
flattened there. This is apparent when the scope is mounted in the rings. The
tube color is very efficient at heating up in sunlight. The tube interior has a
nice flat black coating. The entire optical tube assembly shows considerable
thought and expertise in its design and execution. The 150 is f/5. With its
150mm (5.9") aperture and 750mm focal length, the tube is a short 27 inches in
length. The optics arrived in a state of pristine cleanliness. The primary
mirror has a neat center ring to assist in collimation. Both mirrors have
Celestron's XLT multi-layer reflective coating, which should produce the
brightest images possible for a reflector of this aperture. Popping in a
Cheshire eyepiece revealed the scope to be out of collimation. Since it was
easy to look through the Cheshire and reach the collimation knobs at the
same time, I was able to align it in a few seconds. The collimation knobs
bit difficult to turn, and might defeat a child. The rear cell also has locking
screws to assist in holding collimation. Some sort of membrane covers the
back of the mirror, presumably to prevent dust from migrating into the tube.
The diagonal mirror appeared to be properly placed and aligned,
according to my sight tube. This mirror is glued onto a four-vane spider
which appears to be well designed. The vanes are very thin. Collimation requires
the use of an Allen wrench in three small screws. The 1.25"-inch focuser
is pretty good. Initially, racking it in and out produced an alarming crunching
which I believe was caused by a bit of styrofoam packing material caught
the rack. The large knobs, with their rubber gripping surfaces, are TeleVue-esque
in appearance. Eyepieces are secured with two set screws. This arrangement
looks and feels cheap after years of using only brass compression ring fittings,
but oh well.
The little 30mm finder is mounted on a tall stalk and uses
two-point alignment with a third spring-loaded point of contact. The finder has
good eye relief and a focusing objective, and appears to be quite decent if you
can make do with a small straight-through finder. I replaced it with a 50mm
RACI finder to make finding things easier and more comfortable.
The main telescope's plastic dust cap has a 40mm off-axis
pull-out aperture, for those times when you want to project the sun's image
onto a card, or when you want to guess at what Galileo might have seen with
his telescopes (your view will be much better than his though).
One small issue was that one of the tube mounting rings was
slightly rotated on the dovetail bar, meaning
it was angled on the tube. Attempting to loosen the bolt which attached the
ring to the bar was a challenge. Synta appears to hire one of those gigantic
Chinese basketball players to tighten these bolts. It would not budge, and my
Herculean (by way of Napoleon Dynamite) efforts eventually sheared the bolt.
replaced it and was able to correct the issue.
The CG-4 equatorial head is a cute little handful, a functional
miniature version of a German equatorial mount. It would be perfect for a
smaller telescope, but I suspected it would prove marginal with the 150,
or with any of the Omni XLT scopes except the stubby little 5" SCT. This was
a matter of small concern to me, for reasons which I'll reveal later. The
is well designed and constructed. It has provision for a polar alignment
scope which is not included. The little setting circles are primarily decorative.
right ascension circle is loosely mounted. I did not get motor drives. The
manual knobs provided for the slow motion controls are actually decent, big
and mounted on metal stalks.
The stainless steel tubular tripod, with its 1.75" diameter legs,
should be fine with any of the Omni XLT scopes, and looks especially imposing
with the dinky CG-4 head mounted atop it. Since I tower above the landscape at
6'2", the scope's height on this tripod works well for me, but in some
positions it would be inaccessibly tall for a child.
Finally, the scope comes with a generic 25mm eyepiece with a 50
degree apparent field of view. It seems pretty sophisticated for what is
essentially a freebie eyepiece, with good eye relief and a screw-up eye guard
for adjusting it. With this scope it delivers 30X and a field of 1.6 degrees. With a 5mm exit pupil, this
is as low a power as I would wish to use on this scope.
The telescope makes a good first impression as it stands gleaming
in the sunlight. First light took place on a night of the full moon, which was
somewhat limiting. I will add that this scope looks beautiful in the light of a
full moon. The blue of the tube is visible, and the white parts appear
luminous. So how did it work?
My first impression of the mount was correct: marginal for a
scope of this size. Slight whacks produced vibrations lasting a few seconds,
the exact time depending on the attitude of the scope. However, the scope
remained usable at powers up to 214X. It moved smoothly and freely, and the
manual slow motions were also smooth. I did not find it too difficult to
overlook the slight shakiness of the mount, and I am not inclined to be overly
forgiving about such things.
Focusing on stars revealed an unfortunate, needless drawback of
the scope's design. The focuser is tall, which is inappropriate for a small,
fast reflector. The constricted light path and the large distance between the
eyepiece and the diagonal mirror result in vignetting. If the eyepiece focused
at a point closer to the diagonal, field illumination would be improved. As it
is, full illumination is barely achieved only in the very center of the field,
if at all.
This kind of design is all too common in commercial telescopes.
There is no real reason for it. The telescope should be a couple of inches
longer, and the focuser a couple of inches shorter, to avoid this issue. I
suppose the tall focuser with its long travel is used to maximize the scope's
compatibility with various accessories. It does this at the expense of optimal
visual performance. How much difference this actually makes at the eyepiece is
hard to determine, but I suspect the effect is minimal.
Despite this, the scope produced some pleasant views, though
bright star images at high power were nowhere near as clean as they are with my
refractors. Fainter stars cleaned up better. At 214X, Epsilon Lyrae was
resolved into four decent Airy disks surrounded by fairly neat diffraction
rings. At 107x, M13 presented a powdering of faint stars despite the
illumination of the full moon. Using a 22mm Panoptic eyepiece, I saw sharp
stars occupying the central 80% of the field, typical for an f/5 reflector.
I devoted most of my time to studying Jupiter at 214x. Jupiter,
with its mass of low-contrast detail, is a critical test of any telescope. Any
scope which cannot perform well on this planet is of little interest to me.
That night's seeing was mostly good, with an occasional flicker of a moon or
shifting of the disk. The planet's edge was usually sharp. Detail, however, was
elusive. I got only occasional glimpses of substantial detail. The shadow of
Europa was sometimes visible. Overall it was an uninspiring view, but I decided
not to let a single look at the low-riding planet form my evaluation of the
scope's planetary capabilities, especially without comparing it to a telescope
of known quality at the same time.
Star testing revealed no astigmatism, but did suggest a zonal
error, with a dark ring on one side of focus replaced by a bright ring on the
The focuser stiffened up in the cool temperatures. I will be
among the multitudes who remove the thick paste that passes for grease on these
Chinese focusers and replace it with something better.
The little finder was sharp, but I had to disassemble the
eyepiece to remove some conspicuous bits of plastic debris. It is highly prone
to dewing under my local conditions.
Late on the following night, which was damp and dewy following
the passage of a storm front, I was out again. Jupiter looked as before,
hinting at potential detail. Diffraction spikes off the big planet were
visible, but not overly obtrusive. The telescope must have been better cooled,
because it did better with stars. At 214x I got a neat split of the close
double Pi Aquilae (Rebchis), with a separation of about 1.4 seconds of arc.
Deneb at this power appeared pointy and fairly well defined, and it even star
tested better, with no sign of the zone I thought I saw on the previous night.
The telescope was also much steadier. Now we come to the primary
reason I bought this telescope: I wanted the tripod. I also have an Orion
Skyview Pro mount, which I use with my 92mm refractor. It's an older mount,
with an older tripod, its legs only 1.5" in diameter, and several inches
shorter than the current tripods, even when fully extended. I knew the newer,
taller tripod would make the use of this refractor more comfortable.
I bought the Omni. I swapped its tripod for my older one, resulting in two hybrid
mounts: a superior blend of the SVP head and the Omni tripod, and a fusion of
the CG-4 head with the old SVP tripod, which is more in keeping with the petite
size of that mount anyway. The penguin-colored combination of the nice SVP head
with the Omni tripod gave the 150mm reflector a stable home which pays little
heed to raps, taps, and touches. Clearly, the CG-4 head is not quite up to that
task, at least if you approach it as someone used to steady mounts. The CG-4
will seem luxurious to someone upgrading from a department store scope.
On the third night of testing I conducted a "comparo", one
involving the ancient feud between reflectors and refractors. Yes, it was
6-inch reflector vs. 6-inch refractor, going scopo-y-scopo.
caveat: my big refractor, an Astro-Physics f/9 EDT, is actually a 155mm, while
the Omni is of course a 150. Therefore the little guy started out with a slight
aperture deficit. I could have evened things out by making an aperture mask for
the refractor, but I was too lazy. I used only Nagler and Radian eyepieces to
make these comparisons.
When I set these two scopes up beside each other, I was reminded
of Tolkien's Middle Earth, with an eager little hobbit jumping up and down next
to a tall Elf Lord while crying "I can do that! I can do that too!" And you
know what? The cheap little reflector could
do most of what the exalted refractor could do. Most of it...
The first thing I looked at was the crescent of Venus. Not
surprisingly, except for the diffraction spikes in the Omni, both scopes
produced about the same view. Moving to Saturn, only a degree or so away,
revealed greater differences. At similar powers, the refractor view was
significantly brighter and sharper. No surprises so far. Jupiter got the most
eyepiece time by far. Using both scopes at around 200x, there was, at first,
little to choose between the two. The views were marred by high, fast seeing,
meaning both scopes looked about the same, except for the refractor again being
brighter. Contrast was a non-issue. I could not discern much of a difference
between them. I estimate the Omni has a central obstruction of 25% or more (I'm
not going to stick a ruler down there to find out for sure). That does not
appear to be enough to cause a meaningful reduction in image contrast. I
decided to look at other objects while Jupiter climbed.
One good target was the unequal double star Delta Cygni. The
155mm EDT is a sublime splitter of doubles, and this one is no exception,
rendered as a perfect little pair of jewels. Yet the Omni hung right in there,
also producing a neat split, though not quite as clean as the refractor. I
tried a couple of deep-sky targets, even though the sky was already growing
lighter due to the nearness of moonrise. Here the refractor showed its superior
light grasp, offering sweet views of M13 and the Ring Nebula which were quite a
bit brighter, and a bit clearer, than those in the Omni. Yet the views in the
Omni were respectable and enjoyable, in the same league, just somewhat dimmer
and not as pristine.
With Jupiter at the meridian, I returned to that. Now, with the
planet barely above the worst effects of seeing, the 155 EDT pulled ahead,
offering views of Jupiter which were impeccably crisp. The view in the Omni was
softer-edged, but impressively, it revealed nearly the same detail as the
extremely high-end refractor. The Great Red Spot was making a transit, and was
visible with similar ease in both scopes. I was more impressed by the
similarity of the views than by their differences. I decided to add a third
telescope to the mix, my 92mm A-P Stowaway refractor, probably the most
optically perfect telescope I own. Its view of Jupiter was much dimmer than
either of the other two scopes, of course, but the detail revealed was not far
behind the Omni. In overall performance, the $400 Omni was midway between these
two fabled refractors, and closer to the big one than the little one.
With my mounts spread thin, I put the Stowaway on the CG-4 for
this three-way shootout. It worked okay, but was distinctly more wiggly than
the SVP. I would prefer to limit the CG-4 to smaller scopes, such as an 80mm
refractor, a 90mm Maksutov, or a small solar scope such as the Coronado PST.
I then turned all three scopes to Izar, Epsilon Bootis. All
showed this fairly close, unequal double beautifully. The Omni was the worst of
the three, but not by any great margin. This time I thought the view in the
Stowaway was best, as its fat, hard Airy disks displayed the star colors
For the fourth and final night of my test, I used the Omni to
view various deep-sky objects during the brief window between the end of
twilight and the onset of moonrise. At 95x, I had a nice view of M51, with a
suggestion of a swirly pattern. At the same power, M81 and M82 were two bright
lights barely fitting in the same field of view, two galaxies with very
different personalities. With an OIII filter in place, the Dumbbell Nebula was
big and bright, with traces of wispy detail across its face. Using Radian
eyepieces for 95x and 62x, stars were sharp across the entire field. The
cluster M71 in Sagitta was a dense, pretty enhancement of the Milky Way star
Backing off to 34x with the 22mm Panoptic eyepiece, the entire Coat
Hanger asterism fit into the field, a pattern of bright, sharp stars. My pond-side
observing spot is hardly a prime dark sky site. It will be interesting to try
the Omni in a true dark-sky location.
The Omni XLT 150 costs less than 10% of what I paid for the large
A-P refractor in 1994, yet it offers about 70% of the visual performance, in a
package that weighs less than half as much. I can transport and use this scope
without giving much thought to preserving my investment. Today you could pay
more for counterweights and tube rings for a 6-inch apochromat than the total
cost of the Omni. It is a surprisingly serious stargazing tool for very little
money. No observer need be embarrassed to use such a telescope. A diligent
observer could occupy himself for years with this scope. It would be fine for a
Messier Marathon, and quite feasible for logging the Herschel 400 from a dark
site. It was a lot more pleasant to use on the stable, driven SVP mount than on
the supplied CG-4, but it's still useable in its native form.
For my small investment of $338, I not only got the taller tripod
I wanted, but a fine 6" reflector as well, plus a neat, though limited, little
equatorial mount which I may or may not keep. This is the third 6" f/5
reflector I've owned, so I have a good idea of what to expect from them.
As far as I can remember, this one gives up nothing to its two predecessors.