1) TMB Fluorostar 4" f/8 APO refractor
2) 20" Obsession
3) Celestron CR150 6" refractor
By Ed Ting
(Note from Ed: Are we really up to "Page 10" already?)
Click on a scope below:
1) TMB Fluorostar 4" f/8 APO 10/17/99
(4" f/8 triplet refractor, 7X50 finder, $2300-$2800)
From Thomas Back comes a fine new line of apochromatic refractors.
I saw Back's 6" version of this scope at Astrofest this year (1999) and
was dutifully impressed. Along with Roland Christen's expensive glass
in the adjoining booth, these were among the most popular items at the
show on both nights. I received the 4" version as a review sample,
and couldn't wait to put it through its paces.
Another great 4" refractor -- the TMB Fluorostar
The mount is the GM-8
These scopes carry optics from Russia, while the optical tube assemblies
are sourced from Taiwan. The optics are designed by Thomas Back and
made in Russia by a Zeiss subcontractor. Back does final bench testing
and star testing on each lens here in the US. If they don't meet his stan-
dards, he sends them back. The Taiwanese connection tends to raise some
eyebrows, but you shouldn't worry. The machining and finish work are first-
rate. The focuser is massive, and carries huge focusing knobs, which look
just like the AP focusers, only larger. A chrome bat-wing handle serves as
the focus lock. The scope comes with a 70 mm extension tube that you can
remove to accomodate a binoviewer without a barlow, if binoviewers are your
The entire tube is finished in a nice metallic pearl-white, with tasteful
gold (yes, real gold) accents. The scope is huge for a 4". If you told
someone it was a 5" refractor, they would probably believe you. The mech-
anical tolerances are very tight. When you extend the dew shield or focus
your eyepiece, a whoosh sound escapes from the tube. The tube is very
heavy, but will work on a GM-8 with only one 7-lb counterweight. For those
looking to save money, the same optics are available in a Vixen-based
mechanical assembly. If you buy this scope, however, you want the
nicer mechanical assembly. Believe me. You just do.
According to Back, these new scopes are true apochromats which are "highly
corrected for chromatic and spherical aberration..." I tend to agree. Two
of us present could not detect any errors in a star test on Vega at 164X.
Detail on the massive focuser
The optics use SD (super low dispersion) glass as the center element, with
two matching hard crown elements as the outer elements. All surfaces are
multi-coated. Light throughput is said to be 96%. Another innovation is
the use of a temperature compensated cell, which is said to maintain precise
collimation and reduce stresses on the lens elements on the objective during
large temperature swings.
We compared this telescope to a Takahashi FS102, which has the same
aperture and focal length. We also had several duplicate sets of eyepieces
on hand, so side-by-side comparisons were easy.
The first thing you notice is that the Fluorostar is impressively well-
corrected for chromatic aberration. I could see no false color at all,
no matter how high I pushed the magnification. I never thought I would
say this, but in comparison, the FS102 almost looks like a semi-apo-
About the only detriment I could find on the Fluorostar is a slight contrast
loss when looking at bright objects. The sky is not quite as dark as in
the Takahashi. Mind you, the effect is mild. According to Back, this is
an inevitable result of having an air-spaced triplet. You win on color
correction but you lose a little on contrast. It all depends on your
priorities. I'll take the superior color correction any day, but the slight
loss in sky blackness caused one observer present to say that he pre-
ferred the Takahashi by a small margin. I also noticed that there are only
three baffles in the Fluorostar, while the Takahashi has eight. (According
to Thomas, he is investigating adding another baffle of some sort, probably
near the eyepiece end.)
Other than that, there isn't much to talk about. The Fluorostar is a
world-class refractor, right up there with the AP, Takahashi, and
TeleVue apochromats. We split some doubles and looked at the
popular early-fall deep sky objects. Both scopes did wonderfully well.
Later in the evening, both the Fluorostar and the FS102 were delivering
stunning images of Jupiter. Again, we noticed the Fluorostar had better
color correction, while the Tak had a blacker background.
While it's hard to predict the future, Thomas Back appears off to an
auspicious start. The Fluorostar feels more like a mature product from a
company that's been around the block a few times than a first effort from
a new company. The scopes are currently available through APM in Europe
or from Thomas himself.
Recommended for discriminating refractor lovers.
Update, 3/26/00: Newer versions of these TMB telescopes are said to
have superior baffling inside the tube, and improved multicoatings. Owners
tell me that these new TMBs have superb contrast. One reader, who also
owns an FS102, says the TMB actually beats the Tak on contrast. While I
have not verified this for myself, if this is true, then these newer TMB tele-
scopes could be really special.
2) 20" Obsession 10/17/99, 8/6/04
(20" f/5 Open Truss Dobsonian, $4995 + shipping, many options available)
(Note: Price is now $5995 as of 8/04)
(Note: See also review of the 18" Obsession)
"Now that's a big telescope!"
Readers have noted to me the relative dearth of premium, large-aperture
Dobsonian reviews in these pages. All I can say is, you people writing
to me from the clear, dry environs of Arizona, New Mexico, West Texas,
and California have no idea how lucky you are. Here in the humid, cloudy
Northeast, such telescopes are overkill much of the time.
Still, large Dobs are gaining in popularity out here. Take the case of
friend David, who ordered this 20" model. He had it shipped to my house
because he was out of town that week. I was glad to oblige -- since I cannot
afford such a telescope (at least not now) I wanted to see what it felt like
to take delivery of a 20" Obsession, even if it wasn't mine.
The scope arrived in 5 huge cartons. I opened the cartons to check for
shipping damage, but that turned out to be something of a joke. The pieces
are so well-packed, it became obvious within 5 minutes that there was not
going to be any damage, not anytime soon. The scope parts come packed
in bubble-wrap, and the whole thing is then covered with self-hardening
foam and placed in the carton. If I had drop-kicked the cartons down the
stairs, I still don't think there would have been any damage. As it is,
it took me nearly one hour of steady work just to unpack everything.
...and it looks even bigger in person, trust me
After another half hour of or so or work, I had the scope assembled, and I
did not even have the instructions. Egads, this is a huge telescope! On
the day I put the telescope together, a bunch of guys from a contracting
company were at the house, replacing my roof. One by one they stopped
in the garage, and the response was pretty universal. They would look
up at the scope, tip their caps back, and say "What the hell is that thing?"
Indeed, for a couple of days, it was hard to suppress a grin every time
I walked into the garage. The eyepiece is something like 8 feet off the
ground, and I need to climb four steps on a ladder just to reach the eyepiece
when it's at the zenith. What's worse, although the scope comes with
detachable wheelbarrow handles, I always place my big Dobs on rolling
platforms, which raises the entire scope another 4"-5".
This telescope is extremely well-made, and as you look it over, the quality
speaks at you everywhere you look. The woodworking on it is fabulous,
much better than it has to be. It is almost a work of art. Other premium
Dob manufacturers make wonderful telescopes, of course, and I love them
all. But in terms of the quality of the woodworking, I still don't think any-
thing touches the Obsession for sheer craftsmanship.
The Nova mirror arrived a few days later, and I spent about an hour installing
it, adjusting the sling, and collimating the scope. For someone used to 4"
refractors and 8" Newtonians, as I am, this 20" Obsession took some getting
used to. While looking at M13 in twilight, I picked out NGC6207 nearby while
the sky was still blue. This was going to be fun.
As darkness settled in, I toured the late summer and early fall deep sky
objects. You can see much structure and detail in familiar objects like
the Ring, Dumbbell, M13, M15, M11, M33, etc. The Dumbbell looks more
like a Football Nebula than a Dumbbell. The various clusters in Cassiopeia
and Cygnus take on real personality (in "normal" sized scopes, they tend
to look like identical fuzzy blobs.) Planetaries like the Blue Snowball
or the Blinking Planetary can be pushed to huge magnifications without
image breakdown. To give you an idea of the light grasp of a scope like
this, M56, the little globular in Lyra, looks like M13 in an 8" reflector.
The scope moves very smoothly on both axes - just a little nudge and it
goes where you want it to. I got used to climbing the ladder. Also,
I trained myself to sight through the Telrad from the ground (yes, from
about six feet away.) This turned out to be a useful skill.
On the second night, I spent most of the evening looking at Stephan's
Quintet, the Veil (with a 35 mm Panoptic and a 2" O-III filter) and the
H-II regions in M33. The Veil, by the way, is absolutely spectacular,
with its various tendrils and wisps twisting and intertwining with each
other. Very beautiful. Night after night, I found myself looking up at
the sky from my car on the way home, hoping it would be clear enough
to use the Obsession.
20" Obsession, with shroud attached
TeleVue Ranger, foreground, left
Drawbacks? OK, so it's huge. Your wife is going to have a heart attack
when she first sees it. Also, you really do need access to fairly dark
skies to make the best use out of it (although a rural location like my
Mag 5.0 driveway is adequate.) Being able to leave it fully assembled
and on a rolling platform (i.e., the way I have it set up) will encourage
you to use it. Finally, you are going to be a collimation expert after
a few nights with this scope. The act of slewing the scope from one
side of the sky to the other over the course of the evening tends to
throw the collimation off.
15", 18", 25", and 30" versions are also available (if you buy one of
the 30" models, please invite me over!) There are too many options to
list here; check Obsession's website for the latest updates and prices.
Delivery runs anywhere from three to nine months.
I was looking for a way to close this review by telling you how much
I like this telescope. On the fourth clear night with the Obsession,
several club members stopped by the house for a long evening of
observing (I had this telescope at the same time as I had the Fluorostar,
above, which made me a popular guy around here for a while.) After the
session, I wheeled the scope into the garage and put the mirror box cover
back on. At this point, one observer wrapped his arms around the truss
tubes, looked lovingly up at the eyepiece end of the scope, and said,
softly, "Come to Pappa..."
Y'know...recommendations don't come any higher than that.
3) Celestron CR150 6" Refractor 11/23/99
(6" f/8 achromatic refractor, CG5 mount, 9X50 finder, 20 mm Plossl, $1199)
This brand-labeled telescope from the Far East has been available in Europe
under the "Bresser" name for some time. I saw a Bresser sample at Astrofest
this year (1999) and was impressed by the quality of the scope's images. Now,
Celestron is selling the scope as the CR150.
Celestron's 6" achromat. Ignore the ads; this is the
correct balanced position of the optical tube.
This telescope has generated a huge amount of excitement online, and I
have been flooded with requests in e-mail asking for my opinion of it. It
certainly looks enticing. The telescope appears to carry the triple-threat
of large aperture (for a refractor), short focal length, and low price. The last
point is worth emphasizing, as a 6" Astro-Physics costs $4995 and a one
year wait for the optical tube alone, and the 6" Takahashi OTA lists for over
The scope is large - the OTA weighs over 18 lbs, and you need two 11 lb
counterweights on the mount to balance the tube. This is not a scope
for kids. The CG5 mount (a clone of the Super Polaris, which claims a
maximum load of around 15.5 lbs) is really too small and lightweight
to hold a tube of this size. There's nothing inherently wrong with the
supplied mount, it's just a little light for an 18 lb tube. For best results
you should get something on the order of a GP-DX, or even better, a
Losmandy GM8. With the CG5, the scope looks top-heavy and vibra-
tions intrude at powers over 150X or so.
Also, Celestron's ads are a little misleading, showing the tube attractively
balanced with the front of the tube pointed high in the air. In reality, the
scope is so front heavy that you have to slide the OTA waaay up front
to achieve proper balance.
Finally, there is an air of cheapness in the whole product. The scope's
little brother, the C102HD, also exudes this cheap feel, but since the
C102HD is so much smaller, you don't notice it as much. This isn't an
indictment of the CR150, it's common sense - you get what you pay for.
Your $1199 goes towards the optics, not towards artsy fit and finish.
The scope is supplied with a 9X50 finder mounted on a stalk with an
innovative spring-loaded mechanism that allows you to align your finder
very quickly. There's a 20 mm Plossl that looks like a clone of the old
silver-top Vixen Plossls, a 2" visual back, and a 1.25" diagonal. The
tube has three baffles inside and the coatings on the objective are a
deep, rich green color. The 56 page instruction manual is unusually
thorough and well-written, although I found the section on astrophoto-
graphy to be a bit optimistic.
I was both excited and skeptical about this telescope. A 6" f/8 achromat?
And one that sells for only $1199? According to who you choose to listen
to, a conventional 6" doublet achromatic refractor not employing special
glass elements needs to operate between f/18 and f/27 to suppress false
color to acceptable levels. F/8 sounds way too fast.
The scope shows modest undercorrection. And yes, there is false color
on bright objects like the Moon and Jupiter. However, it isn't objectionable;
I expected far worse. The mount is okay but starts wiggling a little too
much when you get up over 150X (and you are going to want to, the optics
are quite good.)
We had the scope out next to an Astro-Physics Star 12ED, a 120 mm
f/8.5 apochromat. The cheap Celestron made out far better than either
of us expected. Once you get past the false color, the images are
razor sharp, and the generous aperture allows you to resolve some
incredible detail on the planets. On a dimmer target like Saturn, the
brighter images in the CR150 actually made detail like the C ring, as
well as detail in the rings themselves, stand out better. It was also
easier to count Saturn's moons in the Celestron.
Jupiter had a modestly bright ring of purple around it at powers over
125X or so. If you can look past it -and some people have the ability
to do this better than others- the gas giant showed some impressive
detail. There wasn't anything we could see in the AP that we couldn't
see in the CR150. The AP's views were more pleasing to the eye
however, due to its lack of color. Images of both Jupiter and Saturn
were still holding up at 253X, and I felt that we could have pushed the
CR150 even higher if we wanted to.
On deep sky, the scope is also impressive, supplying pinpoint, con-
trasty images on the Double Cluster and NGC457. I can't wait to get
this telescope out on a clear, moonless night to go galaxy hunting.
As the evening wore on, I found I was able to overlook the scope's
faults (the modest false color, and the too-light mount) because the
optics were so pleasing. Also, the owner eventually put the scope
on a GM8, which tightened things up nicely. The CR150 on a GM8,
by the way, makes for a very nice rig that you could live with for a
I think the Celestron CR150 is an ideal star-party scope. It's big,
which will impress the kids. It's large enough to withstand accidental
bumps, has excellent optics, but isn't quite enough of an heirloom to
make you worry all the time. I also think it's a good scope for ambitious
Celestron CR150 Hots
Celestron CR150 Nots
Some false color
Front-heavy tube makes for awkward-looking setup
A taste of Refractor Heaven for only $1199...
...but start saving those pennies for a bigger mount
Update, 11/28/99, 3/26/00: This is a really nice telescope, and its performance
belies its low price. Compared to a truly superb refractor like an Astro-Physics
or a Takahashi, however, there are a couple of areas where it falls short.
The first, obviously, is in the CR150's false color, which I think becomes intrusive
around 175X-200X around brighter objects. The entire FOV in the eyepiece is purple-
colored when looking at Jupiter at 253X. However, if you can look past this, the scope
will show you a lot of detail. Seeing is an art as well as a skill, and tuning out the
false color in any achromat is a part of this skill. If the purple halos really bother
you, try inserting a #8 (light yellow) filter in the eyepiece.
The second area where a scope like this falls short is in its ability to take high
power. On an inexpensive scope like this one, images remain sharp as you push
the power up, then they crumble and break down rapidly after a certain point. On
this particular CR150 sample, this "cliff effect" occurs around 300X. The star test
begins to look pretty bad at 350X. In contrast, a world-class apochromat like an
AP will keep showing you detail even as you push the scope to stupid-high powers.
Under the right conditions, the atmosphere, not the scope, becomes the limiting
factor. I am reminded of a recent superb evening when the AP130 was holding up
on Saturn even at 500X+.
Still, in the end, 300X is nothing to laugh at. The CR150 is a telescope with
optics solidly in the "very good" category, and which, happily, sells for a very
reasonable price. But you should not expect miracles of it, nor should you buy
one as a substitute for a true apochromat if you happen to have a very critical
End Telescope Reviews, Page 10
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