This Celestron spotting scope puts good quality Maksutov-Cassegrain optics for long-distance observing (both terrestrial and astronomical) into a compact and lightweight body that's easy to use in the field.
This Celestron spotting scope has:
• 90mm f/13.3 Maksutov-Cassegrain optics
• 45° viewing angle diagonal (eyepiece holder)
• upright/right-reading images suitable for both terrestrial and astronomical use
• 8 x 21mm erect image finderscope
• built-in T-threads for easy 35mm or DSLR camera attachment
• 32mm Plössl eyepiece (38x)
Like all Maksutov optics spotting scopes, such as the ultra-premium Questars, the Celestron C90 is exceptional for observing anything that is small and distant and needs a lot of power to resolve clearly. It provides sharp, high contrast images of distant birds and wildlife, details that are free from the distracting spurious color you'll find in comparably-priced achromatic refractor spotters. Optically very nice, this Celestron 90mm Maksutov has the optical performance to keep you busy observing the land and sky for many years to come.
Features of this Celestron spotting scope . . .
Maksutov-Cassegrain optics: 3.5" (90mm) aperture, 1200mm focal length, f/13.3 multicoated optical system. The 11" long optical tube weighs only 3.1 lbs with finderscope and eyepiece attached.
Multicoated optics: The system's Maksutov corrector lens is fully coated on both sides with multiple layers of antireflection materials for high light transmission and good contrast.
Internal focuser: Focuses by moving the primary mirror fore and aft in the optical tube by means of a large focusing knob on the rear cell.
Close focusing: Twenty turns of the slow, but very precise, focusing knob of the C90 moves the focus from the horizon down to a very close 20'. This is not as great a burden as it might first seem, as only a few turns of the knob in the middle of its rotation range will cover most of the medium to long distance observing situations the C90 is designed for. However, the relatively slow multi-turn focusing makes the C90 more suitable for observing stationary targets from distant locations, rather than trying to follow fast-moving birds in flight.
Erect image eyepiece holder: Unlike conventional 90° star diagonals (eyepiece holders) that reverse the image, the supplied 45° viewing angle erect image 1.25" diagonal provides correctly-oriented images that are identical to what you see with your unaided eye (upright and correctly oriented left-to-right so that printing is correctly oriented and readable and you can easily follow subjects in motion).
Eyepiece: Fully multicoated 1.25" 32mm (38x) Plössl eyepiece with a 1.4° field of view (73' at 1000 yards). While this Celestron C90 Mak has excellent optics with sharp images, its field of view is somewhat narrow, due to the scope's long focal length. However, the narrow field is entirely in keeping with the primary task of the scope, that of long distance observing. The eyepiece has a usable eye relief of 18mm for eyeglass use. In addition, any of nearly 200 different 1.25" astronomical eyepieces can be used with the C90, giving exceptional flexibility in choosing observing magnifications. For example, the optional Celestron 8mm to 24mm zoom eyepiece listed below provides very flexible viewing, with a zoom range of 50x to 150x, allowing you to instantly modify the magnification to suit the target distance and lighting conditions.
Finderscope: 8 x 21mm straight-through crosshair design with erect right-reading images that give you the same image orientation you see with your unaided eye. Three collimating screws let you line up the finder crosshairs precisely with the center of the eyepiece field. The finderscope must be removed from the scope before the scope is stored in its case, but a quick-release dovetail bracket makes removing the finder just a matter of seconds. The finder can be reinstalled on the scope just as quickly, and the dovetail bracket system assures that the finder will be properly lined up with the main optics once in place on the scope. The finderscope eye relief is quite short at 8mm. It will severely vignette the field of view for eyeglass wearers.
Tripod adapter: The scope has a mounting shoe with two standard 1/4"-20 thread mounting holes to let you use it on any suitable heavy duty photo tripod. The front hole is for visual use. The rear hole will help better balance the scope on the tripod when a camera is attached for terrestrial photography.
Built-in camera adapter: The star diagonal holder threaded onto the Cassegrain focus at the rear of the scope has standard T-threads built in that allow you to connect a 35mm or DSLR camera to the scope by simply adding an inexpensive optional T-ring to fit your camera. This converts the C90M to a very high power 1200mm focal length (24x) f/13.3 telephoto lens for long distance terrestrial nature photography. Such high magnification requires the use of a very sturdy photographic tripod for the sharpest images.
Carry case: Nylon backpack style carrying case.
