For 30 years, TeleVue has pushed the boundaries of APO refractors, as well as eyepieces, to the recognized pinnacle of performance. We were gratified but not surprised that Backyard Astronomer's Guide said of the NP101: "optics don't get any better than this." No wonder Sky and Telescope rated the NP101 tops and selected it as the test instrument for its landmark review of the SBIG STL11000 CCD camera . The "is" versions of the TeleVue-60, 102i, NP101 and NP127 retain the exemplary wide field and planetary visual capability while adding new features to make imaging easier and more flexible. We were determined to make the NP series optically, mechanically, and functionally as perfect as possible for imaging up to 50mm diagonal chips without penalty to its near ideal visual operation. (Reviewer Note.) How? By applying the developments created for the TeleVue-60is to the new NP101is and NP127is and then going beyond. The NP101 (540mm, f/5.4, 4") and NP127 (660mm, f/5.2, 5") maintain their optical specifications yet with redesigned 4-element optical systems. Larger rear lens groups absolutely minimize vignetting in formats up to 50mm diagonal. For these large chips an optional field corrector was developed (Reviewer Note.) so the corners of the newly brightened edges would virtually be as perfect as the center of the field. Next, to take full advantage of the larger lenses, we developed a larger focuser and draw tube having a 3" front aperture and 2.4" rear aperture. This eliminates any restriction of the larger diameter converging light cone. We build and test the rack and pinion focuser to hold 12 lbs. of weight, yet still permit extremely fine focusing control via a 10:1 dual speed pinion assembly. This new draw tube also permits quick change from visual to imaging operation and allows full camera rotation without focus change. In addition, it has the capability to correct for any residual focal plane tilt and accepts a "position stop" for our digital micrometer to allow repeatable focus measurement to 0.0001". To maintain squareness to the optical axis while changing camera orientation, the draw tube has three lock screws that tighten against a taper on the "imaging insert" ring. This insert is threaded to accept TeleVue's new Imaging System accessories including large diameter extension tubes, optical accessories, and camera and CCD attachments, all with mating threads. (Reviewer Note.) The Focusmate 10:1 planetary ball type reduction focuser provides extremely sensitive focus adjustment, measurable with the optional Digital Micrometer Kit to better than 1/10,000". Also, the optional Focusmate Driver permits electronic motor control of the focusing process. The Focusmate Driver has direction push-buttons and adjustable speed. A tap on the button permits vibration-free focusing in steps as small as approximately 0.0005". Specifications Type APO (Nagler-Petzval) Refractor Elements / Groups 4 / 2 Objective (mm) 101 Focal Length (mm) 540 Focal Ratio (f/#) 5.4 Length OTA (inch) 25.5 Length with diagonal (inch) 28.5 Weight OTA/Std. Config (lbs) 10.7 / 10.7 Drawtube/Focuser 2.4-inch, Focusmate dual-speed rack/pinion Maximum Visual Field (deg.) 4.9 (with 2-inch 55mm Plossl) Maximum Recommended Power (x) 250
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