An apochromat for the masses.
I REMEMBER MY FIRST LOOK THROUGH an apochromatic refractor many years ago. While wandering around the observing field at a star party, I came upon one of the original Astro-Physics 5-inch apo refractors. The view of Saturn stopped me dead in my tracks. It's hard to describe in words, but the image seemed somehow more real, more there. Sure, the big Newtonian reflectors gathered more light, and the Schmidt-Cassegrains were more portable, but I was drawn to the purity and clarity of the image through the refractor. I spent a lot of time that night looking through the apo. By the end of the evening, I knew two things: I wanted one in the worst way; and, sadly, I couldn't afford one.
A refractor, which uses an objective lens to bring light to a focus, also acts as a kind of weak prism, breaking up white light into its constituent colors. Typically, blue light comes to a focus closer to the objective than does red light. Known as chromatic aberration, these differing focus points produce false color in the telescope's image, which is often seen as a blue or purple halo around bright stars. An achromatic objective, which consists of two pieces of dissimilar glass, brings the focus points of the colors much closer together than a single lens can. Good achromats can yield outstanding images, but the false color never completely goes away, and it is generally more pronounced in instruments with low f/ratios. Unfortunately, once you have learned (or have been taught) to see this colored halo, you can never unlearn it.
Astronomers have lived with false color in refractors since the invention of the telescope early in the 17th century. Recently, however, advances in glass technology have resulted in a new breed of refractors that are essentially free of false color (at least at visual wavelengths). These apochromatic objectives typically have lenses made from extra-low-dispersion (ED) glass or fluorite, which dramatically lower the chromatic aberration. (By the way, achromat means "without color," while apochromat means "without color--but, we're serious this time." If someone invents a refractor with color correction superior to that of an apochromat, we're going to have to come up with a new name.)
For many amateur astronomers, a fine apochromatic refractor remains the Holy Grail of telescopes. The problem has always been--and my beleaguered checking account can attest to this--cost. A thousand dollars per inch of aperture is not unheard of in the world of premium apos. To make matters worse, some topnotch models have waiting lists that stretch several years into the future. This has even led to situations where some used telescopes sell for more than their original purchase price. There seemed to be no justice in the high-end refractor world.
In the midst of all this comes a remarkable new 80-millimeter f/7.5 ED refractor from Orion Telescopes & Binoculars. During my many years of reviewing telescopes, I've never before seen the kind of initial interest that was shown in this little refractor. Within days of Orion's announcing the telescope, online message boards and newsgroups were flooded with claims that fell broadly into two camps. One group said that the little 80-mm scope is the best value in all of astronomy, while the other claimed that the telescope couldn't possibly be any good given its low price. The online debate was, shall we say, spirited. And this was before anyone had actually used the scope!
The Real Story
I was certainly anxious to get hold of one of these new scopes so that I could cut through the hype and see for myself how well it performed. The unit described here was purchased anonymously, and I tested it for about a month. The scope was used alone and in the company of several high-quality refractors of comparable aperture. During my tests I suddenly became a popular guy as curious club members often came by just to see how the little scope was doing.
I'm not going to keep you in suspense. This is a terrific telescope, and it's one of the great bargains in astronomy today. You should read the rest of this review, but in short, if you're aware of the issues involved with purchasing a telescope as an optical tube only and you are reasonably well versed with the various mount and accessory options available, then you can feel safe ordering one right now. What's more, I'm going to get the caveats out of the way first, so I can get on with the rave.
As an optical tube only, the 80-mm ED comes with no mounting rings, no diagonal, no eyepieces, no finder, and (most significantly) no mount. I have already heard from novices who assumed that the $429 price was for a complete telescope outfit. Be careful. The scope comes with a little metal mounting block on the bottom of the tube that has a 1/4-20 threaded hole, which fits standard camera tripods. But this is not adequate for supporting the weight of the telescope. You should order a pair of Orion's mounting rings for its 100-mm AstroView refractor ($16.95), or, if you want to splurge, get a nice set of hinged rings from Parallax Instruments ($125; www.parallaxinstruments.com). The clamshell ring that Tele Vue uses for its large refractors (Genesis, TV-102, TV-101, TV-NP101, and TV-NP127) also fits the scope. You really do need rings, so don't skimp on this.
You also need to put the scope on a good mount and tripod. It's well matched to any solidly built German equatorial mount. Orion offers several suitable ones, including the AstroView ($219) and SkyView Pro ($329) units. Both of these require only one of their supplied counterweights to balance the tube. Fitted with Tele Vue's clamshell ring, the 80-mm apo will fit on a Tele Vue Gibraltar altazimuth mount.
Once you get the mount situation straightened out, you can move on to other accessories for the scope. Orion sells several finders, including 6 x 30 straight-through ($39.95) and right-angle, correct-image ($49.95) models. In addition to a magnifying finder, for my tests I also fitted a unit-power Rigel Systems QuikFinder ($39.95) to one of the rings from Parallax.
Orion offers a 1 1/4-inch mirror diagonal ($54.95), which worked well for me. The scope will accept a 2-inch diagonal, if you're so inclined (see the box below). If you've been in the hobby for a while, you're likely to have some or all of these items and a set of eyepieces already. If not, then you can expect to spend an extra $400 to $600 to get a complete telescope.
With the scope mounted and accessorized, it was time to go observing. A star test revealed the optics to be very good, with textbook diffraction patterns showing inside and outside of focus at 100x and 150x (using 6- and 4-mm Tele Vue Radian eyepieces, respectively). Pushing the magnification to 200x, I could detect a slight asymmetry in the diffraction pattern. Realistically, though, most observers are not going to push any 80-mm telescope to 200x very often.
What was particularly impressive to me was the lack of false color in the scope's images. Stars were white against a black background, and only when the scope was pushed to ridiculously high magnifications on very bright, blue stars, such as Vega, did I start to see a slight blue halo. Even then, this false color was difficult to see. For one of my tests I set up an older 80-mm f/11 achromat (a good scope in its own right) next to the Orion. Images were cleaner, whiter, and crisper in the apo. Putting the Moon just outside the field of the Orion 80-mm resulted in very little glare showing in the eyepiece--a sign that the scope's two light baffles inside the tube were doing their job.
Sampling the Celestial Menu
I was lucky enough to have the scope during the recent Mars opposition, and the little Orion showed impressive detail on the surface of the planet. The bright, white polar cap was easy to spot, as were Syrtis Major and a handful of other well-known dark features. The scope showed the Cassini Division in Saturn's rings almost all the way around the planet, as well as at least three moons.
I spent some time hunting down double stars. Old favorites such as Polaris, Albireo, and Epsilon Lyrae were easy, so I moved on to more challenging targets. I was able to split Epsilon Arietis (5th-magnitude components separated by 1.4 arcseconds), which is very close to the Dawes limit for this 80-mm telescope. The instrument just barely split Delta Cygni, which, at 2 1/2 arcseconds, is not an especially close pair, but the wide disparity in brightness of its 2.9- and 6.3-magnitude components makes it a challenging object for most 4-inch refractors. The view of Delta Cygni wasn't exactly exciting--a broad brightening on the first diffraction ring--but the fact that the scope could delineate its components at all is a testament to its performance.
An 80-mm refractor isn't the first tool you think of for serious deep-sky observing, but used judiciously, it will show you a lot. All of the northern summer and fall Messier globular clusters are easy targets for this instrument, and some of the larger ones (M13, M5, M3, M15) start to show granularity around their edges at 100?, hinting at the countless individual suns making up these clusters. Under sufficiently dark skies with an oxygen-III nebula filter, the scope revealed the eastern and western halves of the Veil Nebula, as well as portions of the nebulosity between them. An O III or ultrahigh-contrast filter enhances the scope's view of the famous planetary nebulae M57, the Ring, and M27, the Dumbbell. And, in a real surprise, I caught the California Nebula with a hydrogen-beta filter.
These results are all very encouraging. But to see how the scope performed objectively, several observing friends and I set it up alongside some highly respected refractors of comparable aperture. First up was my Tele Vue Ranger, a 70-mm f/6.8 ED refractor ($700) that Tele Vue bills as a semi-apochromat. The Orion had better color correction and slightly brighter images. Other than those two qualities, the scopes performed similarly, though the smaller Ranger didn't quite manage to split Delta Cygni.
We also compared the Orion to Tele Vue's TV-76, a 76-mm apo ($1,200). The TV-76 is one of my favorite small telescopes. The pair ran neck and neck throughout the comparisons. In the dark, it was sometimes hard to tell which scope you were looking through, based on the images. This was quite impressive. Only at very high powers (200x and above) did we detect a slight breakdown of the images in the Orion scope. It was also starting to show some false color at these high powers, while the TV-76 stubbornly refused to show any color at all.
In other respects, however, the Orion is not a match for the premium Tele Vue. The TV-76, like all Tele Vue scopes, has beautiful mechanics, while the Orion has a functional but workmanlike tube. The TV-76 is much smaller, which is something to consider if portability is important to you.
So in some ways you get what you pay for. But in other ways you don't. Orion's 80-mm ED apo gives you optical performance far better than you might expect, given its price.
After my formal tests and comparisons were over, I decided to relax and just observe. You can learn a lot from such casual sessions. It is one thing to use a telescope for tests, but when it comes time to observe for the sheer joy of observing, will you reach for it? I'm happy to report that the Orion 80-mm got just as much attention as the other scopes in the field. It never lacked for observers or for targets.
The Orion 80-mm ED refractor is a terrific little performer and a tremendous value. If you have been thinking about buying one, and as long as you understand the cautions I've mentioned, I urge you to do so. This is the most exciting telescope I've seen come down the pike in a long time. Kudos, Orion!
Orion 80mm ED Apochromatic Refractor
What we liked:
* Excellent optics in a portable package
* Good mechanical quality
* Low price
What we disliked:
* Mounting block inadequate for this
Orion 80mm ED Apochromatic Refractor: 80-mm f/7.5 refractor with two-element objective and Crayford-style focuser that accepts 2- and 1 1/4-inch eyepieces.
US Price: $429 (sold as optical tube only)
<ADD> Orion Telescopes & Binoculars (and selected dealers) PO Box 1815 Santa Cruz, CA 95061 Phone: 831-763-7000 www.telescope.com </ADD>
Another Outstanding Value
By Dennis di Cicco
The new 2-inch star diagonal from William Optics is the perfect accessory for the Orion apo (or any other telescope that needs one). And like the apo, one of its outstanding features is its remarkable dollar value. Bargain hunters can find 2-inch diagonals that cost less, but I know of nothing that approaches the quality of the William Optics unit, even at twice its US $99.95 price, which includes a 1 1/4-inch adapter.
From the knurled thumbscrews to the copper compression locking rings (for the diagonal and adapter), the stylish body is 100 percent precision-machined metal. There are no cast-metal parts. Even the name is engraved on the eyepiece holder rather than being silk-screened. The diagonal's nosepiece and the adapter are both threaded for standard 2-inch filters.
At the heart of the diagonal is a 10mm-thick mirror with a stated surface accuracy of 1/10 wavelength of light. Its enhanced aluminum coating offers 97 percent reflectivity. (For those pushing the limits, there's a $199.95 version with a dielectric coating offering 99 percent reflectivity.)
This star diagonal is available for online purchase in North America from William Optics as well as from selected dealers worldwide. Details are at www.william-optics.com or by calling 714-209-0388 (California).
Much of ED TING's astronomical schedule is divided among public presentations at school and civic gatherings and reviewing equipment for Sky & Telescope and his Web site, www.scopereviews.com.
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|Publication:||Sky & Telescope|
|Date:||Feb 1, 2004|
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