Tele Vue NP101is 4" f/5.4 4-Element APO Refractor Telescope, Ivory

Concept: CCD cameras have challenged telescope optics beyond anything ever placed at the focal plane. Tele Vue knew it's APO objectives were up to the challenge, & with the proper tweaks would be extraordinary tools for the imager. With Tele Vue Imaging System (is) telescopes, they have refined their instruments & optional equipment beyond anything a CCD chip has seen.It started small (literally) in 2005 with the Tele Vue-60is & available Digital Micrometer Kit. Achieving critical acclaim with the 60is, Tele Vue was encouraged to further develop "is" telescopes & accessories to maximize aperture, real field coverage & performance, & to make the processes easier for the imager.For 25 years, Tele Vue has pushed the boundaries of APO refractors, & eyepieces, to the recognized pinnacle of performance. They 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 & selected it as the test instrument for its landmark review of the SBIG STL-11000 CCD camera. The "is" versions of the Tele Vue- 60, 102i, NP101 & NP127 retain the exemplary wide field & planetary visual capability while adding new features to make imaging easier & more flexible.Tele Vue-NP101is Tele Vue-NP127is:Tele Vue was determined to make the NP series optically, mechanically, & functionally as perfect as possible for imaging up to 50mm diagonal chips with out penalty to its near ideal visual operation.How? By applying the developments created for the Tele Vue-60is to the new NP101is and NP127is & then going beyond. The NP101 (540mm, f/5.4, 4") & 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 so the corners of the newly brightened edges would virtually be as perfect as the center of the field.In order to take full advantage of the larger lenses, a non-vignetting focuser was developed to prevent any restriction of the larger converging light cone. The draw tube has a 3" front aperture & 2.4" rear aperture. This new draw tube also permits quick change from visual to imaging operation & allows full camera rotation without focus change.In addition, it has the capability to correct for any residual focal plane tilt & accepts a "position stop" for Tele Vue's 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 4 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, & camera & CCD attachments, all with mating threads.