Celestron CPC Deluxe 925 HD Computerized Telescope CPC Deluxe HD Manual - Page 20

TELESCOPE BASICS A telescope is an instrument that collects and focuses light. The nature of the optical design determines how the light is focused. Some telescopes, known as refractors, use lenses. Other telescopes, known as reflectors, use mirrors. The EdgeHD optical system (Aplanatic Schmidt) uses a combination of mirrors and lenses and is referred to as a compound or catadioptric telescope. This unique design offers large-diameter optics while maintaining very short tube lengths, making them extremely portable. The EdgeHD system consists of a zero power corrector plate, a spherical primary mirror, and a secondary mirror along with a set of field flattening lens integrated into the baffle tube. Once light rays enter the optical system, they travel the length of the optical tube three times. The optics of an EdgeHD telescope has StarBright XLT coatings - enhanced multi-layer coatings on the primary and secondary mirrors for increased reflectivity and a fully coated corrector for the finest anti-reflection characteristics. Inside the optical tube, a black tube extends out from the center hole in the primary mirror. This is the primary baffle tube, and it prevents stray light from passing through to the eyepiece or camera. FIFGigUuRrEe 54--11 A cutaway view of the light path of the Edge HD A cutaway view of thoepltiigchatl pdaethsiogfnthe EdgeHD optical >> Image Orientation The image orientation changes depending on how the eyepiece is inserted into the telescope. When using the star diagonal, the image is right-side-up, but reversed from left-to-right (i.e., mirror image). If inserting the eyepiece directly into the visual back (i.e., without the star diagonal), the image is upside-down and reversed from left-to-right (i.e., inverted). This is normal for the Schmidt-Cassegrain design. Actual image orientation as seen with the unaided eye Reversed from left to right, as viewed with a Star Diagonal FIGURE 5-2 Inverted image, as viewed with the eyepiece directly in telescope >> Focusing The CPC's focusing mechanism controls the primary mirror which is mounted on a ring that slides back and forth on the primary baffle tube. The focusing knob, which moves the primary mirror, is on the rear cell of the telescope just below the star diagonal and eyepiece. Turn the focusing knob until the image is sharp. If the knob will not turn, it has reached the end of its travel on the focusing mechanism. Turn the knob in the opposite direction until the image is sharp. Once an image is in focus, turn the knob clockwise to focus on a closer object and counterclockwise for a more distant object. A single turn of the focusing knob moves the primary mirror only slightly. Therefore, it will take many turns (about 30) to go from close focus (approximately 60 feet) to infinity. For astronomical viewing, out of focus star images are very diffuse, making them difficult to see. If you turn the focus knob too quickly, you can go right through focus without seeing the image. To avoid this problem, your first astronomical target should be a bright object (like the Moon or a planet) so that the image is visible even when out of focus. Critical focusing is best accomplished when the focusing knob is turned 18 in such a manner that the mirror moves against the pull of gravity. In doing so, any mirror shift is minimized. For astronomical observing, both visually and photographically, this is done by turning the focus knob counterclockwise. The emblem on the end of the focus knob shows the correct rotational direction for focusing the CPC. FOCUS FIGURE 5-3 >> www.celestron.com