呵呵，10月份啊，最新的一期，牛吧。请版主一周后删除。
这些镜子都很便宜，天狼努力啊！
REFRACTOR ROAD TEST
Celestron Firstscope 80-EQ
Orion AstroView 90
Swift Model 865
Stellarvue 80/9D
Choosing your first telescope can be as daunting as settling on your first car. Astronomy takes four small refractors out for a spin.
Deciding which telescope is best for new stargazers is a favorite activity at astronomy clubs, in online astronomy chat rooms and discussion groups, and at star parties around the world. One reason for this debate is that no one answer will suit everybody. So many considerations must be made before charging ahead and purchasing that first telescope. How much money do you have to spend? Is portability important? What types of sky objects interest you the most?
It's this last question that often tips the balance for neophytes who are trying to choose between the two most popular telescope types: reflectors and refractors. In general, reflectors offer more inches of aperture for the buck, which means these scopes capture more light and resolve fainter objects. But there's a tradeoff: The signature mirrors inside reflectors can wash out some of the contrast in images because they stand directly in the light's path to the eyepiece. So if you're interested in mostly bright quarry, such as the moon, the importance of image quality may eclipse the need for brightness, and it's the refractors' time to shine. Here I review four refractors with apertures between 2.4 and 4 inches (60mm to 100mm), the likes of which have given many lifelong astronomers, including yours truly, their first close-up views of the moon, planets, and brighter deep-sky objects.
Small refractors have gotten a bad rap in recent years, probably because of their distant cousins that are sold in department stores. You know the kind: those toylike telescopes with their nanoscale eyepieces and flimsy mounts. All four of the instruments here are well above that level, and while they do not have Go-to computerized control, they do provide for some good, old-fashioned stargazing.
In an effort to evaluate some of the small refractors on the market today, I gathered a few instruments from their manufacturers: the Celestron Firstscope 80EQ, the Orion AstroView 90, the Stellarvue 80/9D, and the Swift Model 865. All come with extendable tripods and light-duty, manually operated German equatorial mounts, except for the Stellarvue, which was supplied for this test without a mounting. Each mount is similarly equipped with manual slow-motion controls on the right ascension and declination axes, small setting circles, and locking latitude-adjustment screws and reference scales.
Each telescope also comes with several accessories. The Orion and Swift both include 6x30 finder scopes, while the Celestron comes with a red dot "unity finder," which projects a red dot against a reflective window. This lets the observer see both the red dot as well as the sky beyond, allowing him or her to aim the telescope at a selected target. Unlike the 6x30 finders, unity finders do not magnify the view nor do they make dim stars appear brighter. In fact, the Celestron red-dot finder has a reddish coating on its window that reduces star brightness by about one-half magnitude. Finally, the Stellarvue does not include a finder, but one can be purchased "&aagrave; la carte."
Of the two 6x30 finder scopes, Orion's is superior. Not only does it mount to the telescope with an easier-to-adjust mounting bracket; it also yields brighter images. I checked both finders and found that they each produce the same 5mm exit pupil, yet the Swift struck me as dimmer.
In addition to their finders, each telescope comes with a 114" rack-and-pinion focuser, a 90?star diagonal, and one or two eyepieces, again, except for the Stellarvue, explained below. The Celestron comes with 10mm and 20mm MA eyepieces (yielding magnifications of 90x and 45x, respectively); the Orion includes 10mm and 25mm Kellner eyepieces (91x and 36x, respectively), while the Swift includes a 25mm Kellner eyepiece (40x). The Swift has the best eyepiece of the bunch in terms of overall optical quality, but be aware that you'll probably need to add another in the 9mm to 10mm range for acceptable views of the planets.
As mentioned earlier, the Stellarvue is a beast of a different sort. Unlike the others, which are aimed squarely at new stargazers, it is a bit more upscale, both in terms of optical and mechanical performance as well as in the observing experience expected of its user. The base unit includes a very smooth 2-inch focuser, an adapter for 114" eyepieces, a 114" 90?star diagonal, a pair of tube mounting rings, and a red-dot unity finder. The eyepiece adapter is also threaded to accept T-adapters, enabling owners to attach single-lens reflex camera bodies directly for photography. Optional accessories sold by Stellarvue include an imported German equatorial mount, a padded carrying case, a sky atlas, and several other eyepieces and star diagonals. Several of these items, including 9mm and 25mm Pl鰏sl eyepieces, are packaged as the "80/9D Complete System," which sells for about $250 more than the &aagrave; la carte telescope. Because of these two different versions, beginners should be careful to order the right setup, just so they know exactly what they will be receiving in return. If you decide that the Stellarvue is for you, I would recommend getting the 80/9D Complete System unless you already have a mounting for the telescope. For testing this scope, however, I used my own star diagonal and mounting.
Mechanics
Each of the telescopes includes a nicely painted steel tube. All are a glossy white except for the Celestron, which is their trademark black. The finish was excellent on all.
At the front end of each telescope, the achromatic objective lens is held in place with a non-adjustable lens cell. The Orion and Celestron objective cells were made of plastic, pressed together to hold everything in place, while the Swift and Stellarvue scopes used metal cells. All held their lenses properly, except for the Swift. Its locking ring was tightened down so hard that it actually distorted the objective lens elements. As a result of the pinched optics, images did not focus as well as they might were the cell's locking ring tightened properly. Although I would not recommend this procedure for anyone not intimately familiar with the operation, I was able to correct the problem by loosening the cell's lock ring enough to take the pressure off the elements. Once done, image quality improved noticeably, as mentioned below.
Each of the telescopes comes with a rack-and-pinion focuser to accept standard 114" eyepieces. The Stellarvue's 2" focuser, which includes a 114" adapter as standard, was the smoothest, although all worked pretty well. The Stellarvue's two oversized knobs have a very nice ergonomic feel to them, making fine adjustment a snap.
The Swift, Celestron, and Orion refractors come on German equatorial mounts and adjustable aluminum tripods. The identical Celestron and Orion mounts, known as the Celestron CG-3 and the Orion EQ-2, respectively, are the sturdiest. Even though the Orion weighs about 1.5 pounds more than the Celestron, the mount is still able to support it steadily enough for good observations. Admittedly, some shaking did occur when attempting to focus the telescopes, but that's almost inevitable with mounts like these. The manual slow-motion controls used to move the telescope in right ascension and declination when zeroing in on and tracking an object worked very smoothly in both cases.
I was disappointed with the Swift mount. Unlike the others, which locked down securely when I tightened their screws, the Swift mount's polar axis refused to tighten adequately after I tilted the mount at an angle matching my latitude. As a result, the telescope mount shifted unexpectedly when the instrument was swung from object to object across the sky.
Each telescope was shipped to me directly from its respective company and outfitted with the standard equipment previously mentioned. Assembly went quickly and without incident. The instructions left a little to be desired, however, possibly causing a beginner some grief when assembling the instruments. The Orion had the best instructions, in my opinion, followed closely by the Celestron and the Stellarvue. The Swift manual lacked clear illustrations and would probably conspire to only confuse a new stargazer.
Optics
All of the refractors were tested side by side from my backyard on suburban Long Island over several nights. From my observing location, the faintest star I can see by eye alone is usually between magnitude 4.5 and 5, which is probably typical for a majority of Astronomy readers and potential consumers. As these tests were conducted last winter, I had a choice of several of the sky's finest showpieces as targets.
First, I turned each of the telescopes toward Saturn. Using my own 10mm eyepiece in each, I was able to detect Cassini's division, the dark band between the two bright outer rings, as well as the planet's equatorial zone in all four telescopes. The Stellarvue produced the sharpest view, with Cassini's division appearing as a pencil-thin line separating the A and B rings. The far more subtle Crepe, or C, ring was silhouetted against the planet's bright disk through the Stellarvue. I could also make out the C Ring through the Celestron and Orion scopes, although not as clearly. It was clear using the Swift only after I loosened the objective lock ring.
Jupiter showed a good amount of cloud structure through all four telescopes, with the north and south equatorial belts readily apparent in each. The Stellarvue delivered the best image, highlighting the clouds with several subtle irregularities that remained invisible through the others. Part of this improvement is attributable to the four light baffles inside the Stellarvue tube, which help boost image contrast by blocking stray light. Jupiter certainly improved through the Swift after the pinching problem was eliminated, though it still showed a bit less cloud detail than the Stellarvue. Neither the Orion nor Celestron showed as much contrast as the others.
My first deep-sky target was M42, the Orion Nebula, which I viewed initially through a 25mm Pl鰏sl eyepiece. Once again, the Stellarvue showed the best image contrast, although the Orion's larger aperture was used to good advantage here in producing the brightest image and showing a few subtle extensions of the nebula that went unseen through the others. The Swift's 90mm aperture also produced a bright image, though it did not reveal all of the faint tendrils visible through the Orion.
Switching to my own 7mm Pentax XL eyepiece, I zeroed in on the heart of the nebula - the Trapezium, a quadruple star. All four telescopes had no trouble whatsoever in resolving the Trapezium, although once again, the Stellarvue's optics generated the sharpest star images of the bunch.
Rigel is an excellent test star for small refractors. How a scope resolves its faint companion star, Rigel B, can reveal optical defects such as flaring, and Rigel's own brightness makes clear at a glance how well the scope copes with the Achilles' heel of all telescopes - chromatic aberration. Chromatic aberration causes haloes to appear around images because the scope's main lens separates incoming starlight into its component colors and bends each color at a different angle, so each arrives at a different focal point. While this distortion can never be completely eliminated, these four scopes have a second, corrective, lens nested with the main lens. They all passed the resolution test by showing Rigel B next to its brilliant parent star; but unfortunately, all the scopes also revealed a good amount of chromatic aberration. The Stellarvue showed the least, with no sign of flaring or internal reflections caused by straying star light, while the Orion, though still acceptable, showed the most. Flares around Rigel were seen through the Swift before the pinched optics were corrected. I also saw some minor flaring through the Celestron, indicating its objective was probably being pinched slightly in its cell.
Finally, I put each scope through the star test, which compares two views of a single bright star - how it looks when the focus knob is turned by equal amounts to the left and right of focus. In an ideal refractor, both images should look like identical patterns of concentric, evenly bright rings. If they disagree, then the culprit might be turbulence in the atmosphere, or worse, an optical defect. It's very important that a telescope be properly cooled before attempting the star test, so I left each scope outside for two hours before I began, more than enough time for everything to equalize.
The star test proved that all four telescopes have very smooth optical surfaces, but also showed signs of spherical aberration, which produces blurry images and is caused by slight inaccuracies in curvature of one or both objective-lens elements. The Stellarvue was clearly the closest to ideal, but the others were well within acceptable parameters. Finally, the Swift showed just a tiny bit of astigmatism, causing a point to appear as a line or an ellipse, but once I loosened the lock ring, the problem vanished, leaving only the slightest signs of spherical aberration.
The Bottom Line
Each of these telescopes is a reasonably good performer both optically and mechanically. Any of the four would give a new stargazer plenty of enjoyment when viewing brighter sky objects. The Stellarvue's optical prowess is especially impressive, although the others also held their own.
Celestron Firstscope 80-EQ
CELESTRON INTERNATIONAL
2835 Columbia Street,
Torrance, CA 90503
Phone: (310) 328-9560
http://www.celestron.com/
-Aperture: 80mm
-Focal length: 900mm
-Focal ratio: 11
-Weight: 24 pounds
-Features: 10mm MA eyepiece, 20mm MA eyepiece, 90 star diagonal,
red dot finder, German equatorial mount, tripod
-Typical Retail Price: $270
Orion AstroView 90
ORION ASTROVIEW 90
Orion Telescopes and Binoculars
P.O. Box 1815,
Santa Cruz, CA 95061
Phone: (800) 447-1001
http://www.telescope.com/
-Aperture: 90mm
-Focal length: 910mm
-Focal ratio: 10
-Weight: 24 pounds
-Features: 10mm and 25mm Kellner eyepieces, 90 star diagonal,
6x30 finder scope, German equatorial mount, tripod, adapter
for camera attachment
-Typical Retail Price: $300
Swift Model 865
SWIFT INSTRUMENTS, INC.
952 Dorchester Ave.,
Boston, MA 02125
Phone: (800) 446-1116
http://www.swift-optics.com/
-Aperture: 90mm
-Focal length: 1,000mm
-Focal ratio: 11.1
-Weight of optical tube assembly only: 30.8 pounds (11 kg)
-Features: 25mm Kellner eyepiece, 90 star diagonal, 6x30
finder scope, German equatorial mount, tripod
-Typical Retail Price: $625
Stellarvue 80/9D
STELLARVUE
P.O. Box 7515,
Auburn, CA 95604
Phone: (530) 823-7796
http://www.stellarvue.com/
-Aperture: 78mm
-Focal length: 750mm
-Focal ratio: 9.6
-Weight of optical tube assembly only: 5.5 pounds (3 kg)
-Features: red-dot finder, mounting rings, large focus
knobs, 90 star diagonal, adapter for eyepieces, focuser
-Typical Retail Price: $450 |
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