Telescope Reviews

Page 10 By Ed Ting Updated 8/6/04
(Note from Ed: Are we really up to "Page 10" already?)

Click on a scope below:
  • 1) TMB Fluorostar 4" f/8 APO refractor
  • 2) 20" Obsession
  • 3) Celestron CR150 6" refractor
    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.
    TMB 4 Inch 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 thing. 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.
    TMB Close-up 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- chromat. Really. 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.
    Obsession20 ...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.
    Obsession w/ Shroud 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 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 $10,000. 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 long time. 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 beginners. Recommended. Celestron CR150 Hots
  • Pinpoint-sharp optics
  • Low price Celestron CR150 Nots
  • Some false color
  • Too-light mount
  • Front-heavy tube makes for awkward-looking setup The Verdict
  • 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 eye. End Telescope Reviews, Page 10
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