Meade ETX-90 User Manual - Page 17

OPTIONAL ACCESSORIES Meade makes a complete line of accessories to enable you to get the most fun and performance from your ETX Series telescope. No matter what you want to accomplish, we have the equipment to help you get there. Choosing Eyepieces of view with 48x magnification. This is a very good all purpose eyepiece for your telescope, but you should consider buying additional eyepieces in longer and shorter focal lengths to fully realize the potential of the excellent 90mm optical system in your ETX90 telescope. A telescope's eyepiece magnifies the image formed by the telescope's main optics. Each eyepiece has a focal length, expressed in millimeters, or "mm." The smaller the focal length, the higher the magnification. For example, an eyepiece with a focal length of 9mm has a higher magnification than an eyepiece with a focal length of 26mm. Experienced users know that higher powers are, in general, not as useful as lower powers. Many of the objects in the night sky are relatively large and faint and look best at low magnifications. The power or magnification of a telescope is determined by the focal length of the telescope and the focal length of the eyepiece being used. To calculate magnification, divide the telescope's focal length by the eyepiece's focal length. For example, a 26mm eyepiece is supplied with the ETX90. The focal length of the ETX90 is 1250mm (see SPECIFICATIONS, pages 48 and 49). Telescope Focal Length 1250mm Eyepiece Focal Length 26mm 1250 ÷ 26 = 48.1x The magnification is therefore 48.1x. Low power eyepieces offer a wider field of view, bright, high-contrast images, and long eye relief. To find an object with a telescope, always start with a lower power eyepiece such as the Super Plössl 26mm or longer focal length. When the object is located and centered in the eyepiece, you may wish to switch to a higher power eyepiece to enlarge the image as much as practical for prevailing seeing conditions or, for many objects, the view is best with a high quality low-power wide-field eyepiece. NOTE: Seeing conditions vary widely from night-tonight and site-to-site. Turbulence in the air, even on an apparently clear night, can distort images. If an image appears fuzzy and ill-defined, reduce to a lower power eyepiece. Your telescope comes supplied with a Super Plössl 26mm eyepiece, which gives a wide 1.08 degree field The Series 4000 Super Plössl Eyepieces are excellent well corrected 4 element optics at popular prices. They come in a wide range of focal lengths to give you the right magnification for any type of celestial object you are viewing. You can also use one of the Series 4000 Barlows to double or triple the magnification of a Super Plössl eyepiece. These eyepieces have been the standard for over 30 years. Series 4000 Super Plössl Eyepieces Focal Apparent True Length Type Field Power Field 40.0mm SP 32.0mm SP 26.0mm SP 20.0mm SP 15.0mm SP 12.4mm SP 9.7mm SP 6.4mm SP 44º 31x 1.41° 52º 39x 1.33º 52º 48x 1.08° 52º 63x .83° 52º 83x .62° 52º 101x .52° 52º 129x .40° 52º 195x .27° OPTIONAL ACCESSORIES 17