For 30 years, Tele Vue has pushed the boundaries of APO refractors, as well as eyepieces, to the recognized pinnacle of performance. TeleVue was 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. How? By applying the developments created for the Tele Vue-60is to the new NP101is and then going beyond.
The NP101is (540mm, f/5.4, 4") maintains the optical specifications of the NP101, yet has a redesigned 4-element optical system. The larger rear lens group absolutely minimizes vignetting in formats up to 50mm diagonal. For these large chips an optional field corrector was developed 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, Tele Vue 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. Tele Vue builds and tests 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 four lock screws that tighten against a taper on the "imaging insert" ring. This insert is threaded to accept Tele Vue's new Imaging System accessories including large diameter extension tubes, optical accessories, and camera and CCD attachments, all with mating threads.
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".
|Type||APO (Nagler-Petzval) Refractor
|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 Plössl)|
|Maximum Recommended Power (x)||250|