THE NEXT-GENERATION TELESCOPE FOR AMATEURS

by Dennis di Cicco

     It's the same every month. An unnatural silence falls over our building just after the first shipment of magazines arrives from the printer. All the editors head off to their offices with copies of the new issue to savor the fruits of the previous month's labors. For the first time, wrapped in one neat package is the sum of what we've previously known only from pieces. It's also the first chance many of the editors get to see some of the advertisements in that issue.
     Soon the building comes alive again as the staff begins an informal critique of the issue. That's what happened one morning nearly two years ago when I walked into editor Leif Robinson's office to discuss the May, 1989, issue. We had both been caught off guard by a new ad from Jim's Mobile Industries (now JMI) that announced a radically new telescope design. Although saddled with the unpronounceable name EpocsElet ("telescope" spelled backward!) it was touted as a highly portable 18-inch reflector on a split-ring equatorial mounting.
     Had this scope been designed by someone who missed the Dobsonian revolution? Or was it the work of a person looking toward the future? Dobsonians had become the design for grass-roots observers who shunned astrophotography for the pleasures of eyeballing the universe. But with astrophotography again on the rise, and charge-coupled devices (CCD's) coming within reach of amateurs' pocketbooks, the demand for big equatorial telescopes has returned. Add to this the need for portability to escape ever-increasing light pollution and you have a description of the EpocsElet. (Mercifully, one of the telescope's earliest modifications was a name change to NGT for Next Generation Telescope.)
     In the year that followed, the people at JMI made many changes to the instrument's basic design as they tooled up for production. Last March, as the first units were readied for shipment, I visited JMI for a firsthand look at the NGT-18. I spent the day talking with Jim Burr, the company's owner and driving force, and touring the manufacturing facilities adjacent to his home in the Rocky Mountain foothills west of Denver, Colorado.
     I tried the telescope that night, though conditions were less than ideal. The sky was clear, but wind roared through the mountains with such force that at times it sounded like a passing freight train. We had wheeled the telescope onto the workshop driveway where it stood unprotected. The instrument was buffeted to the point where astrophotography would have been impossible (as it would have been with any other portable telescope). But to my surprise visual observing was only mildly affected. With the clutches on both axes tightened a little more than I would have liked for slewing the scope by hand, the image shook during wind gusts but was reasonable steady otherwise.
     Later, Burr and I talked about the scope and soon found ourselves sitting on the floor examining parts of the declination drive. A letter from Burr outlining changes to the telescope to improve its stability arrived at my office before I returned. According to Burr, these were modifications "to do whatever it takes (within reason) to make this a great telescope!"

TESTING THE NGT-18

By midsummer a production version of the NGT-18 arrived at Sky & Telescope. I was absolutely amazed at how portable it turned out to be. I drive a 1986 Honda CRX. Despite its relatively large cargo area, few would expect this two-seater sports car to accommodate an 18-inch telescope. It did! By sacrificing the passenger compartment to the telescope's nose assembly and primary mirror, everything could be carried with the back hatch left only slightly open. Even the passenger compartment could be reclaimed by leaving the hatch almost fully open, but that might be a problem in highway driving.
     The next pleasant surprise came when I assembled the telescope for the first time. Using nothing more than common sense (even a screwdriver was unnecessary), I unpacked the scope and had it fully assembled with the drive working in under 12 minutes. Later, after gaining experience, the task took less than four minutes!
     Third on the list of surprises was the telescope's collimation. The optics were aligned almost perfectly despite their travels from Denver. The collimation was so good that I decided not to make any adjustments, but these should be no more difficult than for any other fast-focal-ratio Newtonian reflector. I was particularly impressed with how well the collimation was maintained when I rotated the nose assembly to change the position of the eyepiece.
     There are no locks on the nose assembly. Friction alone keeps it in place, but there was no slippage when even the heaviest eyepieces or cameras were attached to the focuser. On the down side, it was difficult to rotate the nose without shifting the scope's aim slightly. But I soon learned to anticipate the best position for the eyepiece before swinging the instrument to a new part of the sky.
     The scope was quite stable, and the modifications to the mounting following my March visit definitely improved the instrument's resistance to wind. The image was rock solid in light breezes. A rap on the tube would shake the image for a few seconds, but the damping time depended on how well the NGT-18 was balanced, where in the sky it was pointed, and especially on the type of surface on which it sat. The floor of my observatory and a hard-top driveway required longer damping times than when the scope was set on bricks placed on a grassy lawn. This last setup, however, gave a "mushy" feel to small slewing adjustments that I made by hand.
     The NGT-18 comes with an electric focuser. At first I considered this an unnecessary luxury but soon found it to be very useful. It was easier to focus precisely with the motor than by hand, which would shake the scope slightly and make it difficult to see when the image was sharpest. Although the stubby focuser has limited travel, a 2-inch extension tube and 1¼-inch adapter accommodated every eyepiece I tried, from a 50-mm wide-field to a 5-mm Plössl. Furthermore, the telescope tube's truss rods have three positions where they attach to the nose assembly, which allows considerable freedom in positioning the focal plane for special applications.
     The 18-inch f/4.5 mirror gave excellent images, with stars appearing as pinpoints on a high-contrast background. Astronomical seeing, not the mirror, always limited the image quality. (It's a rare night at my observing site when any mirror larger than 10 inches reaches its diffraction limit.) The NGT primaries are made by Galaxy Optics, an outfit which is rapidly gaining a reputation for its superb large-aperture mirrors (S&T: November, 1990, page 482).
     To get a feel for the smoothness of the drive, I spent an hour or so guiding the telescope without a camera attached. Periodic error in right ascension was small, uniform, and easy to correct with the push buttons. Much of the credit goes to the mounting's 3-foot-diameter horseshoe ring — the largest driving surface of any telescope marketed to amateurs.
     The declination control uses a stepping motor and tangent arm. It was smooth and responsive, with an acceptable amount of hesitation when switching directions. Since my tests were done mostly with the telescope only roughly polar-aligned, declination drift always occurred in one direction.
     In short, guiding the telescope was easy and could be mastered quickly by even a novice astrophotographer. The drive control has selectable 2x and 4x speed settings for guiding, and I preferred the faster one for declination and the slower for right ascension. Unfortunately, they cannot be set independently. For more comments on astrophotography with the NGT-18 see page 37.

AN OVERVIEW

     Many of the NGT-18's features are shown in the accompanying photographs. With a few exceptions, I was extremely impressed with the telescope. It could be driven to an observing site, unloaded, and made ready for use in the same time as an 8-inch Schmidt-Cassegrain. The NGC-MAX digital setting circles and electronic deep-sky catalogue that come standard with the telescope offer a quick method of polar alignment and easy access to more than 8,000 celestial sights. With the light-grasp of an 18-inch mirror, it's easy to understand why I had a wonderful time hunting down scores of faint objects. The scope worked so well that I would get involved with the view and forget that I was supposed to be doing tests.
     There were only two things I didn't like. Most serious is the limited amount of telescope "tube" that extends skyward past the secondary mirror. When using some 2-inch wide-angle eyepieces you can look "around" the secondary and see extraneous light entering from beyond the front of the tube. My solution was simple — I taped a black-paper shield beyond the tube's end opposite the eyepiece.
     I also didn't like the placement of the on-off switch at the lower left corner of the drive's hand control. Although I never accidentally hit this toggle switch while guiding, that could easily happen and ruin a photograph.
     This telescope stands alone in the marketplace. The closest competition I can think of is the Juno-14 from the Jupiter Telescope Co. in Florida, which is a 14-inch Dobsonian mounted on a d'Autume equatorial platform. The NGT-18 costs more, but it has additional features — particularly larger aperture, full equatorial capability, and the electronic catalogue. Several manufacturers offer larger apertures than the NGT-18 for less money, but only as straight Dobsonian designs. There are also the Celestron 14 and the proposed 16-inch Meade, but these are Schmidt-Cassegrains, not Newtonians. Because of the NGT-18's quality and JMI's commitment to continually improve the scope, it will be the standard by which any future competition is judged.