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Home > Reviews > Telescopes > Refractors > STELLARVUE SV102ED

STELLARVUE SV102ED
By Lawrence Carlino - 9/9/2007

Refractor enthusiasts (and I’m one of them) are fortunate to live in an era where choice abounds. In the ever popular 4-inch aperture, everything from inexpensive traditional Fraunhofer achromats to expensive three and four-element APO’s make the selection of a telescope both exciting and agonizing. Yet, until recently, the vast middle ground that combines near-APO telescopic performance and easy portability with a reasonable price has been largely uninhabited.

The Vixen 102mm, f/6.5 ED scopes are no longer in production, and the Orion and Celestron (Synta) 100mm, f/9 doublets, though reputedly fine performers at a very reasonable price, are simply too long to satisfy airline carry-on requirements. Borg’s modular and highly portable 101ED scopes are available, but at prices that push close to the $1800 mark. The William Optics Megrez 110ED doublet does fit in this limited category, though its very fast f/5.95 focal ratio compromises ideal color correction.

But recently, Stellarvue has entered the arena with the new SV102ED, an ED doublet refractor with a moderately fast f/6.95 focal ratio, a 710mm efl, and a bottom line price of $1095, seriously undercutting the limited competition. The SV comes complete with retractable dew shield, a choice of tube rings or clamshell, a red-dot finder, and a dual-speed rotatable Crayford focuser. Options include an upgrade to a Starlight Instruments Feather Touch focuser, an airline “carry-on” hard case, star diagonals, and a variety of finder scopes and alt-azimuth mounts.

Bound to be popular because of its optical and mechanical qualities, the SV has generated a short waiting list. Stellarvue’s reputation for quality control, hand-made attention, and individual testing of all of their telescopes makes the lack of off-the-shelf availability understandable. My particular SV102ED ,one of the first batch scheduled to be shipped, encountered a delay. A conversation with SV’s owner, Vic Maris, revealed that the scope bench tested well, but it fell short when tested under the night sky: “Good, but not good enough!” A new lens was then substituted for the original in order to achieve SV’s stringent performance mandates.

FIT, FINISH, and MECHANICS

The SV arrived in its optional 22” x14”x9” hard carrying case, the thread-on focuser removed to shrink the telescope’s tube length to a mere 19 inches. The instrument was well- packed, arrived in perfect collimation, and immediately exuded a feeling of quality construction and solidity. The “pearl white” tube finish was strikingly attractive, complemented by the black trim of the focuser, sliding dewcap mechanism, and tube rings. Clearly, this is a very good-looking and professional telescope.

Mechanically, the SV functions well: the dewcap slides with smooth precision, and the standard focuser came as a pleasant surprise. Though not as fine as the legendary Feather Touch, its coarse movements are nicely progressive and linear with no hint of image shift, and the fine focus is equally smooth and easy to control. A collet arrangement allows for the rotation of the Crayford to any desired position.

After attaching the red-dot finder and a CG dovetail plate to the tube rings (one is built in to the clamshell if that option is selected), I mounted the SV on a William Optics EZTouch alt-az mount, a perfect match for grab-and-go astronomy.

OPTICAL TESTING

After enduring the usual new-scope period of overcast skies, I got the opportunity to star test the SV in order to get some preliminary ideas of its optical quality – and the initial results were very encouraging. Using Polaris as a target, I found both the intra and extrafocal Fresnel rings to be dead symmetrical, cleanly defined, and indicative of a well-corrected optical system. There was no trace of spherical aberration or astigmatism, and the out-of-focus patterns displayed only moderate false color.
Stellarvue doesn’t reveal the type of ED glass used in the SV102ED, though I do know that it is NOT FPL-51 or FPL-53. Whatever it is, it does seem to do a fair job of suppressing chromatic aberration – not an easy task with a short-focus doublet configuration.

UNDER THE STARS

Obviously, the ultimate test of telescopic quality comes under real-world observing conditions in the night sky, preferably when direct “A-B” comparison can be made with comparable instruments.

For testing, I had on hand an excellent Celestron (Vixen) 102mm, f/9.8 achromat, a Takahashi TSA-102 triplet APO ( o.k. – not at all fair!), an Orion 100mm, f/6 achromat, and a Celestron 6-inch Schmidt-Cass. Recent experience with 2 Borg 101ED’s and a William Optics Megrez 110ED also formed a basis for comparison.

With Jupiter hanging rather low in the southern sky, I put the SV to the test. With a top-quality dielectric star diagonal and a TeleVue 7mm Nagler Type 6 in the drawtube, the image of the giant planet was quite impressive at 101x. Mediocre seeing and differential refraction at this altitude created the expected red and violet fringes, but none of the purple halo endemic to achromats. Detail was sharp and clean with color prominent in the North Equatorial Belt, several EZ festoons, and the well-defined dark dot of a Ganymede shadow transit. The Great Red Spot (on another occasion) could be seen with little difficulty as could the tiny black shadow of Europa. In contrast to the SV’s performance, the short-focus Orion achromat threw up a massive blob of detail-robbing purple around the planet at similar magnification, and the Celestron f/9.8 achro showed a much less intense but noticeable purple halo, though it did show Jovian detail about as well as the SV. As expected, the Takahashi TSA-102 triplet significantly outperformed the SV and the other scopes: no hint of false color, dead sharp contrast, and absolutely authentic color rendition. The image in the SV appeared to be of a “warmer” hue, containing more red which seemed to momentarily flash around the edges of the planet when the seeing deteriorated – barely visible at 101x, but noticeable at 203x when a 3.5mm TV Nagler Type 6 was employed. Overall, however, the SV turned in a very impressive performance when pitted against a much more expensive “reference” instrument.

When compared to the duo of Borg 101ED’s that I owned not too long ago, the SV102ED delivered a sharper image with better detail rendition and slightly superior contrast, but the Borgs exhibited slightly better color correction, though also with a bit of red excess. It appears that many of these ED doublets are optimized to largely eliminate the dreaded “purple haze” at the expense of leaving a touch of unfocused red. Perhaps my unusual sensitivity to red light is a contributing factor where this color balance is concerned; many observers may find the ruddy coloration less noticeable.

The moon, observed from thin waxing crescent to last quarter, was a striking sight with the Stellarvue. The rugged lunar surface showed a remarkable level of detail with no hint of spurious color at 101x. The stark gray expanse appeared to have the same color authenticity of the 6-inch Celestron SCT that I used for comparison.

A couple of days past lunar first quarter, the SV revealed impressive detail near the orb’s northern pole and the chain of tiny coalesced craterlets near Copernicus at 142 and 203x. However, the Tak TSA rendered a slightly sharper image and made the tiniest features easier to see – not a huge difference – but one that would be noticed by an experienced observer. In moments of turbulent seeing, the SV displayed flashes of red and violet around the lunar rim and in the shadows of craters. Compared to the feast of wild coloration generated by the achromatic scopes at similar high powers, the SV’s small chromatic error was barely perceptible.

The SV102ED also performed admirably when challenged by some difficult double stars. The classic test, Epsilon Lyrae, was resolved into 4 sharp pinpoints at only 70x, and the quartet served up nicely defined Airy disks and fairly thin first diffraction rings with the power pushed to 284x with a Burgess/TMB 2.5mm planetary eyepiece. The authentic, almost pure white color of the stars was compromised just a bit at this high magnification as it took on a slight yellow cast. This however, was worlds better than the profound yellow-green that achromats generate.

The close Zeta Aquarii and Delta Cygni were resolved without difficulty at powers of 125x and above, and the beautiful triple Iota Cass was cleanly defined and impressive.
Epsilon Bootis, however, did again point up one of the SV shortcomings: excess red. On brighter red or orange stars, the spillover of red around the edges, particularly during poor seeing conditions, caused “flashes” of red (and sometimes violet) in the first diffraction ring. The color-perfect Tak TSA-102 triplet did not show the effect, nor did the 6-inch Celestron SCT. Overall, however, the SV put on a fine show. There is no question that the scope easily meets the diffraction-limited criteria and performs at a level far closer to a true APO than that of an achromat.

Through all of these observations, I found that the SV performed well with almost all eyepieces of decent quality. Naturally, premium oculars such as the TV Naglers were the best, but even inexpensive generic Plossls yielded very solid, tight images, making it unnecessary for the scope’s prospective user to invest a small fortune to get excellent results from the high-quality objective lens.

On deep-sky showpieces, the SV102ED really shined. In fact, the SV gave up nothing to the Tak TSA-102 when it came to magnitude penetration and image brightness. The nicely multicoated lenses and effective baffling of the inexpensive doublet came into play here as they rendered wonderful contrast, a stygian black background, and pinpoint stellar images. With a TV 19mm Panoptic yielding 37x, the Double Cluster in Perseus became a stunning field of tiny needle points that gave off the characteristic sparkle that only good refractors seem to deliver. Views with the Tak TSA and SV were virtually identical and very pleasing.

Testing magnitude penetration by observing the 13th magnitude star next to M 57, I found again that the SV equaled the more expensive scope in making the star visible with direct vision . With the f/9.8 achromat, however, averted vision was necessary to reveal it.

Scorpius’ brilliant M 6 and M 7 galactic clusters once again illustrated the Stellarvue’s fine deep-sky performance at 37 and 55x. Only here did the Tak TSA do just a little better. The turbulent air close to the horizon affected the SV a bit more, causing the brightest cluster stars to display momentary flashes of red or blue – not at all bad, but not quite as color-pure.

THE COMPETITION

Until recently, the chance of finding an affordable, short efl, high-quality 4-inch ED telescope was nearly zero. Orion’s 100mm, f/9 ED doublet (and its Celestron and Skywatcher clones) did break the price barrier, but with a telescope too long and bulky for some applications. Borg’s 101ED series, though wonderfully versatile because of their modular construction, seem better suited for photography and ccd imaging – and they are considerably more expensive .

I did own a William Optics Megrez 110ED for a few days and had to return it because of some serious optical defects. I’m sure that most of these scopes are good performers and can’t make a valid judgment based upon only one example, but I can state with certainty that their color correction falls behind that of the SV by a significant margin.

Finally, the just-released Astro-Tech AT102ED, at $995, is undoubtedly the SV102ED’s chief competition. I haven’t looked through one of these scopes yet, but I can confirm that it is NOT a clone of the Stellarvue ( different lens, tube, and focuser) despite the almost identical aperture and f/6.95 focal ratio. I’m anxious to do a side-by-side comparison test.

CONCLUSIONS


In my opinion, the SV102ED breaks new ground in providing an affordable high-quality refractor to a range of enthusiasts who cannot or will not ante up the big bucks for a top-of-the-line 4-inch APO refractor. While not quite a true apochromat, the SV102 provides very good color correction that distances it from even the best long-focus achromats. With a lens that minimizes other aberrations, it consistently delivers sharp, high-contrast images that are bound to please all but the most finicky observers.

The scope is well-built, solid, yet not too heavy; and it’s perfectly suited to airline carry-on travel. The optional Feathertouch focuser, finderscope, carrying case, mount, and other accessories make it highly versatile as well.

Finally, and perhaps most importantly, the individual star testing performed by Stellarvue’s Vic Maris on EVERY SV scope ensures that the purchaser always gets a telescope that performs to his or her expectations. Not every manufacturer can make that claim.

Clear and steady skies,
Larry Carlino

Click here for more about this subject. -Ed.

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