Vixen VC200L 8" VISAC Telescope
By the Astronomy and Photography Online Staff
Vixen (www.vixenoptics.com) is Japan's #1 telescope manufacturer and respected for their high quality products by astronomers around the world. Many Vixen telescopes incorporate unique design elements and their flagship VC200L is no exception. The VC200L (item #5870) is Vixen's premier, 8" (200mm) clear aperture, 1800mm focal length, catadioptric telescope (CAT). This f/9.0 modified Cassegrain represents the state of the art and it is among the most sophisticated 8" scopes, of any type, available today. It incorporates Vixen's Sixth Order Aspherical Catadioptric (VISAC) design and is intended to out perform standard Schmidt-Cassegrain telescopes (SCT), an assertion we planned to check against our Celestron C8 control telescope in the course of this review. The corrector plate of conventional Schmidt-Cassegrain telescopes corrects spherical aberration, but not coma or field curvature. The VC200L with VISAC corrects all three aberrations. It is, naturally, made by Vixen in Japan and comes with a five year warranty. The 2011 MSRP is $1899 for the VC200L optical tube assembly.
For astro imaging, the VC200L delivers astrograph quality. Here is what Vixen claims:
"The VISAC system provides high-definition star images to the edge of a wide viewing field and offers exceptionally outstanding performance in astrophotography. Even at the edge of the 35mm film format (larger CCD chips) stars are sharp (smaller than 15 micrometers). This is smaller than the resolution of fine quality CCD cameras, which means that the telescope does not limit the image quality. With its elaborate aspherical optical design, it achieves excellent image correction throughout the large illuminated field. (42mm diameter fully illuminated.)"
The VC200L's unusual optical path extends from the primary mirror in the bottom of the seamless aluminum optical tube to the secondary mirror held in rigid alignment by a four-vane cast spider at the top of the optical tube, back down through a three-element refracting corrector lens system in the light baffle tube extending through the hole in the center of the primary mirror, and out to the eyepiece.
There are advantages and disadvantages to this design. On the plus side of the ledger are the superior optical correction, a Crayford focuser that eliminates all mirror shift, elimination of the dew problem endemic to Schmidt-Cassegrain and Maksutov-Cassegrain front corrector lenses (the VC200L's main tube serves as a deep dew shield) and much shorter cool down times due to the open main tube. The obvious drawback is the open front of the optical tube that admits dust and debris, just like a Newtonian reflector. A less obvious disadvantage is the diffraction caused by the spider and a rather large secondary mirror obstruction that, inevitably, decreases contrast. (The VC-200L's secondary obstruction is 40% by diameter compared to 33.8% for a Celestron EdgeHD 8.)
The aspherical primary mirror in the VC200L is held in place by a retaining ring, rather than edge clips. This is claimed to decrease flare and increase contrast. Altogether, the VC200L is an extremely sophisticated, high quality telescope assembled with obvious care. Evidence of this is also found in the multiple collimation adjustments. You first adjust the secondary mirror tilt, then the primary mirror (if necessary). Even the drawtube/corrector lens system's alignment can be adjusted. (Our test scope's collimation was good out of the box and we kept our hands off the adjustments.) Due to its very rigid, cast aluminum, four-vane spider that is integral with the front cell, the VC200L holds its collimation better than most other open tube scopes, including all of the Newtonians we have used. Unlike a Newtonian, it should not have to be aligned frequently and certainly not for every session. However, its collimation is undoubtedly more fragile than an SCT or Mak and the VC200L deserves to be treated gently.
The VC200L that is the subject of this review was shipped with a carrying handle, full length Vixen dovetail mounting rail with steel mounting surface, 7x50mm straight-through finder scope, finder scope mount and 2" flip mirror star diagonal. Front and back caps for the telescope and finder scope were included, but not for the star diagonal.
The flip mirror diagonal is unusual. It is quite large, but allows straight through, as well as 90-degree, viewing (hence, the flip mirror feature). Eyepieces are retained by a thumbscrew sans compression ring. The back of the diagonal also accepts T-rings for mounting SLR cameras, eliminating the need for a T-mount adaptor. It is a handy diagonal for astrophotography, less so for visual use.
The 7x50mm finder scope focuses for distance (infinity) at the front and to your eye (for a sharp cross hair) at the integral eyepiece. It features an Illuminated cross-hair reticle, powered by a CR2032 lithium battery. The whole cross hair illuminates, not just a dot in the center. A rheostat to control brightness is located on the side of the finder's eyepiece tube. Made in China, it is a decent finder scope and the instruction sheet is printed in Japanese and English. The main body of the finder scope, as well as the mount, is white to match the VC200L optical tube
The supplied finder scope bracket is a good one. It uses three Allan head set screws (wrench provided) near the rear of the mounting tube to secure the scope and three thumbscrews at the front to align the finder with the main telescope. The thumbscrews have locking nuts to retain alignment once set. The mounting foot, naturally, fits the quick release Vixen shoe provided on the VC200L, as well as most other amateur telescopes.
Focusing the VC200L is by means of a smooth, 2" Crayford focuser attached to the back of the main tube, NOT by moving the primary mirror, as is the case with most Schmidt-Cassegrain telescopes. A thumbscrew provides adjustable tension to prevent focuser creep when heavy eyepieces or cameras are used. It was immediately apparent that the VC200L's Crayford focuser is superior to any CAT we have previously used. It focuses like a high quality refractor, smooth and precise. 8" aperture, f/9-f/11 CAT's have a lot of inherent magnification, so a good focuser is very important, as well as a great convenience. Focusing has long been the Achilles' heel of CAT's that focus by moving the primary mirror (Celestron, Meade, Orion, Sky-Watcher, etc.). The latest VC200L's are advertised as coming with a two-speed focuser, but our sample was supplied with the optional single-speed focuser. It worked very well.
The VC200L is available as an OTA (optical tube only that includes the handle and Vixen mounting rail), with the accessories included with our test scope, or bundled with three different Vixen mounts. The latter include the GPD2, Sphinx SXW and Sphinx SXD. Since we already had a GPD2 mount on hand, we requested the basic OTA sans mount. Getting the accessory package (that we did not request) with the telescope was a pleasant surprise.
Along with the VC200L and its usual accessories, our friends at Vixen supplied one of their new #5449, 2" dielectric-coated star diagonals (2011 MSRP $179). This is a high quality star diagonal with a machined, internally baffled, two-piece body. The 1/10 wave mirror is made from quartz glass and boasts 99% reflectivity. It fully illuminates a 2" field of view without any vignetting and delivers true color images. A 1.25", compression ring, eyepiece adaptor is included. (Oculars in both the 2" and 1.25" openings are secured by compression rings to prevent scratching ocular mounting barrels.) End caps are included and it comes with a 5-year warranty. Since we preferred the #5449 star diagonal to the bulkier, flip mirror, two-way diagonal supplied with the VC200L, we used it for all of our critical viewing.
Needless to say, we had been anticipating the arrival of our VC200L. When it finally arrived at the beginning of June, after a long winter delay, we could hardly wait to get it outside under clear skies. Unfortunately, the weather during June and July in western Oregon is often unreliable and 2011 proved to be to be one of the worst years on record, with persistent overcast, clouds and occasional rain showers. Our opportunities to use the VC200L were frustratingly few and far between, trying our (already limited) patience.
We at Astronomy and Photography Online are primarily interested in visual astronomy and we tested the VX200L with our Mark 1 eyeballs. (After all, we reason, there are myriad outstanding astronomical images online and it is becoming increasingly pointless to replicate the effort already expended just to duplicate them.) We are willing to postulate that the VC200L's 42mm circle of full illumination, superior correction and flat field make it photographically superior to other CAT's. If astrophotography is your game you need read no farther, the VC200L is the 8" CAT to own.
To assist in our evaluation, we had a 4.5" Stellarvue SVT115T APO refractor and a Celestron C8 Starbright XLT to keep us honest, as well as a good selection of 1.25" and 2" oculars from Vixen, Celestron, Tele Vue, Meade and Burgess Optical in focal lengths from 40mm (45x) down to 4mm (450x). Here, listed by focal length, magnification and power-per-inch of clear aperture are some of the oculars we used in the VC200L at various times:
The VC200L is really too big for comfortable terrestrial use, but our first chance to look through the big Vixen was during daylight. This gave us an opportunity to align the finder scope on a fir tree atop a distant hill, prior to taking it out at night for astronomical observing. Terrestrial observing let us check the VC200L's close-focusing distance, contrast, color saturation and overall terrestrial imaging ability using eyepieces of known quality. It also gave us a chance to use the Vixen flip mirror star diagonal in its straight-through viewing mode. (Convenient to look through, if you do not mind an upside-down, reversed view of the world!)
For convenience, we mounted the VC200L on a Stellarvue MG alt-azimuth mount and tripod. The MG is basically a medium size German Equatorial head turned 90-degrees. This rugged mount is intended for 4.5" f/7 (or smaller) refractors weighing up to about 15 pounds. The VC200L's weight is at this mount's upper limit and its magnification is probably beyond. However, the MG, although marginal, proved up to the task. For terrestrial use, an alt-azimuth mount is much nicer than an equatorial mount. (We later found the MG suitable for "quick look" astronomical use with the VC200L.)
Looking at the needles on the branch of a fir tree at a laser ranged 130 yards with a 32mm eyepiece, the central obstruction became visible as a round "shadow" in the center of the field of view. This focal length is too long for daylight observing. A 40mm Meade 5000 (2") ocular made the central shadow irritating, which is a shame, as the relatively low (45x) magnification would otherwise be quite useful in the daytime and the true field of view is great. Switching to a 25mm Celestron X-Cel (1.25") ocular (72x) improved matters and, although a faint shadow from the secondary could still be discerned, it was far less intrusive. We would say that 25mm is about the longest focal length ocular generally useful for terrestrial viewing.
Observing a branch in another fir tree lasered at 90 yards through the 25mm ocular, is was easy to see delicate gray moss growing at the base of the branch. Actually, quite interesting. Switching to an 18mm Tele Vue Radian eyepiece (100x) made the image larger and eliminated the remaining shadow of the secondary mirror housing, but the reduced contrast and color saturation, plus the magnified air movement, made viewing less pleasurable. (This on a mostly overcast day with a temperature of 73-degrees F.)
At 90 yards with an 18mm Radian, the focuser had exhausted its travel. There was only about 1mm of over-travel left. We would say that approximately 90 yards, depending on the ocular used, represents the VC200L's near focusing distance.
We made an unfair comparison to a Stellarvue SV115T 4.5" aperture refractor, focused on the same clump of moss. At the same 100x magnification (using an 8mm Radian in the refractor) it was clear that the refractor produced higher contrast and visual "snap," making it easier to see small details. Of course, the relatively short focal length (800mm) refractor, without a secondary obstruction, could be used at much lower magnification for highly detailed, wider field views.
All well and good, but it was time to get the Vixen out at night. The first chance to do so was on 16 June and Saturn was in a favorable position for viewing shortly after sunset. The evening weather was generally clear at our rural observing site, with a low temperature of about 50-degrees F after a daytime high in the low 70's. There was some light pollution from nearby residences, but less than would be found in a suburban setting.
Its rigid handle made attaching the VC200L to our M2 alt-azimuth mount easy. The chances of dropping the scope are much reduced with a handle that provides a secure grip. It is both a convenience and safety factor. The top surface of the handle also serves as a camera mount for piggyback photography and incorporates a ¼"x20 camera mounting screw for this purpose. The latter might also be used to mount a green laser pointer or red dot finder to assist in aiming the telescope. Either would be much easier to use than the straight-through optical finder we had to work with. (An upside down and backward finder drives us crazy.)
Saturn was available for viewing in the southwestern sky as soon as it got dark, so that is the object we observed. After using a 32mm eyepiece to get the telescope on target (our usual strategy for star hopping), we switched to an 8-24mm Click-Stop Zoom. We quickly discovered that the area between 18mm and 12mm gave the best results, so we switched to Tele Vue Radian oculars in those focal lengths. Both gave good views of the exotic planet, with the shadow of the ring system visible against the planet's surface. The 12mm, during brief moments of steady seeing, seemed to show a faint cloud band on the planet's surface. We would rate this view of Saturn under the prevailing conditions as good. Unfortunately, a thin cloud layer developed around midnight, putting an early end to observing.
In the course of viewing, we noticed that star images were, indeed, pinpoints from the center of the field of view to the edge. Vixen's claim that the VC200L offers a highly corrected, flat field of view is no idle boast. We also found that, with the telescope pointed up at a steep angle, it was necessary to use the focuser's tension screw to avoid creep with the heavy 2" star diagonal and an ocular on the back of the scope. Just a bit of tension did the trick and the focuser remained smooth, precise and a pleasure to use.
On the night of 20 June, the clouds dissipated and the sky cleared, leaving a night of good seeing (4 out of 5). This time we mounted the big Vixen on the GPD2 equatorial mount and, for comparison, a Stellarvue SV115T APO refractor on the MG mount. The two telescopes together made an impressive sight.
We were particularly interested in looking at M51, the Whirlpool Galaxy, through the VC200L. The Whirlpool seems to hang below the handle of the Big Dipper (Ursa Major) and was well positioned in the sky. Under very dark sky conditions and with the right telescope, this flat-side-on spiral galaxy is one of the most impressive objects in the night sky. Unfortunately, although the seeing was good, the sky was not quite dark enough to make out the spiral galaxy's arms. We could see the companion galaxy through both telescopes, but no real detail in either. We used 40mm, 32mm, 25mm and 18mm oculars before deciding that 25mm gave the best view. Naturally, the shorter focal length eyepieces made the subject appear larger, but dimmer. The view through the 25mm seemed a reasonable compromise. Using our best "averted imagination," we could vaguely detect lighter and darker areas in the Whirlpool.
The Stellarvue SV115T did not do as well on M51. Given its substantially lower magnification with any given eyepiece, the image was smaller, but no more detailed. We were seeing the usual fuzzy spot marked by increased brightness at the center of the galaxy.
M13, the great globular cluster in Hercules, was an impressive sight through both telescopes. Both gave very sharp views of the stars, but the VC200L resolved deeper into the core of the cluster. It produced a noticeably brighter view at similar magnification. The flat viewing field of the VC200L was appreciated and made accurate focusing on off center stars possible. We are disappointed to report that the ambient light pollution, although not great, impeded resolving M13 to its core. We had hoped that the ultra-sharp VC200L might be able to achieve this.
We quickly tired of trying to peer through the VC200L's straight through finder with the telescope pointed high in the sky. Back and neck strain made this very uncomfortable. Indeed, we found it easier to aim the Stellarvue at an object, turn on its green laser pointer and aim the VC200L where the laser was pointing. A 40mm eyepiece in the VC200L had sufficient field of view to allow us to find the laser beam and follow it to the target.
Alberio, the gold and blue star pair at the foot of the Northern Cross (Cygnus) was inspected last. This 3.1-5.1 magnitude double is 35 arc-seconds apart and easily split. Through the VC200L, the different colors of the two stars were evident. Brightness not being much of an issue, we tried a variety of oculars of increasing magnification, with the shortest being 8mm. Alberio is one of the most beautiful double stars in the heavens and the VC200L handled it nicely.
It was now 2:00 AM and everything was sopping wet from the heavy dew, including our StarBound observing chair, so we decided to pack it in. Unaffected by the dampness, however, was the primary mirror of the VC200L. Its deep tube design (and judicious use of the front lens cap) demonstrated its worth on this night. Given our long experience with the type, we can say with certainty that the corrector of an 8" SCT would have been thoroughly covered with dew.
We had hoped to get the VC200L out at least once more before publishing this review and the weather/seeing conditions finally relented on the night of 8 July. The moon was it its quarter phase, which flooded our remote site with unwanted reflected light, it was windy and there was substantial air boiling after a 77-degree F day. The overnight low was about 50-degrees. The observing conditions went from below average to something approaching average as the night progressed and were the primary factor limiting what we could see, but at least we were finally able to get the Vixen VC200L and a Celestron C8 Starbright XLT in the field together at a remote site in the hills.
Chuck Hawks, Jim Fleck and Bob Fleck were in attendance and a surprise addition was Editor Gordon Landers, just returned from a star party in Likely, CA with his new Stellarvue SV160, a 6.3" APO triplet (oil spaced) refractor with a 1300mm focal length that retails for $8990 online. We were able to compare the three telescopes at approximately the same magnification while viewing the moon, M51 (Whirlpool galaxy), splitting the "Double Double" in Lyra and M57 (Ring nebula). Finally, we aimed the two CAT's at a star field in the Milky Way.
Note at the outset that these are three superior telescopes. The Celestron C8 XLT is the least expensive and it is a better scope than most people will ever own. (A review of this particular C8 can be found on the Astronomy and Photography Online index page.) We were comparing the expert class Vixen to an advanced class Schmidt-Cassegrain and an expert class, one of a kind refractor. We were in telescope Nirvana!
Moon: Earth's binary planet/satellite is the most highly detailed object we can view in the heavens and the only planetary object we observed. We all agreed the Stellarvue refractor demonstrated its superior contrast by providing the best views. However, both the VC200L and C8 revealed plenty of lunar detail, limited more by the local atmospheric conditions than the telescopes themselves. Chuck and Jim thought that the Vixen edged out the Celestron for lunar viewing, while Bob had the opposite impression of the two CAT's.
M51 Whirlpool Galaxy: All three telescopes showed the Whirlpool and its smaller companion as fuzzy areas with a bright center. None of them showed clear dust lanes or spiral arms. Bob thought the SV160 provided the best view, followed by the C8 and the VC200L. Jim rated the C8 first, VC200L second and SV160 third. Chuck concluded that the VC200L and C8 were equal and liked the view through both slightly better than the view through the SV 160. Gordon thought that all three scopes were too close to call.
"Double Double" in Lyra: Splitting the binary star pairs showed the SV160 to its best advantage. All three scopes could easily resolve all four stars with a variety of oculars, but the separation was clearest when viewed through the Stellarvue. Comparing the two CAT's, Chuck and Gordon slightly preferred the VC200L, Bob slightly preferred the C8 and Jim rated it a tie.
M57 Ring Nebula: To no one's surprise, the famous Ring in Lyra showed clearly in both CAT's. Gordon had the Stellarvue on globular clusters M4 and M80 while Chuck, Jim and Bob compared the CAT's on M57. All three rated the two 8" scopes essentially equal when viewing the ring.
Star Field: At one point in the session, Chuck pointed the VC200L at a random star field in the Milky Way, using the 40mm Meade 5000 2" eyepiece. The relatively dense spread of pinpoint star images from edge to edge of the wide field of view was one of the most spectacular views of the evening. Jim pointed the C8 at the same general area of the Milky Way, but the C8 could not match the Vixen's superior correction. The VC200L's sharpness and flat field were displayed to good advantage by this test, which was the VC200L's most dominant moment. It would clearly be a superior CAT for viewing open clusters and similar applications where edge to edge sharpness is at a premium.
The VC200L's 2" focuser is more convenient to use with a 2" star diagonal than the C8 (and most other SCT's). You just slide in any standard 2" diagonal. This makes switching from 1.25" to 2" oculars a snap. With a C8, you have to unscrew the 1.25" visual back and screw-on the proprietary Celestron 2" star diagonal.
The Vixen's other undeniable attribute is its Crayford focuser, which we found clearly superior to the moving primary mirror focusing system used in the C8 and other SCT's. All four observers agreed that they found the Vixen's focuser easier to use and more precise.
Keep in mind that viewing through any astronomical telescope is a subjective experience. It depends as much or more on the existing conditions, eyesight and experience of the observer as it does the telescope. As they say in advertising, but seldom mention in telescope reviews, your results may vary.
As you might expect from its generous clear aperture and rather large secondary obstruction, the Vixen VC200L is primarily a deep sky telescope. It has the focal length and consequent magnification to provide good views of the moon and planets, but cannot equal the contrast of an APO refractor. It is when observing deep sky objects that it is superior. We would rate it a good all-around astronomical telescope and excellent for deep sky use. As of this writing, the VC200L scores second only to the (five times more expensive!) SV160 at the top of our "Astronomical Telescope Comparison" article. (Available on the Astronomy and Photography Online index page.)
As Astronomy and Photography Online's Jim Fleck likes to point out, for most amateur astronomers with 8" and smaller scopes, planetary observing is limited primarily to the moon, Mars, Jupiter and Saturn. Venus' phases can be observed, but no surface details can be seen through its 100% cloud cover. Everything else is a deep sky object and there are thousands of them to observe. Thus, according to Jim, deep sky capability should take precedence over planetary capability in a general purpose amateur telescope.
If this analysis makes sense to you and you are ready for an 8" instrument, give the Vixen VC200L serious consideration. Its initial purchase price is higher than most 8" CAT's, but its pinpoint star images and flat-field view are impressive and its focuser is superior. Given its excellent quality and performance, it should be a lifetime investment.
Copyright 2011 by chuckhawks.com. All rights reserved.