User manual ORION TELESCOPES & BINOCULARS 80MM F 7.5 ED REFRACTOR

[. . . ] Optional tube rings can also be used to mount the scope to a telescope mount. Tube rings with an inner diameter of 100mm (3. 9"), such as Orion item #7371, are needed. If you are using tube rings, you should first attach them to your telescope mount and then lay the optical tube in the tube rings. Use of Optional Eyepieces, Diagonal, and Finder Scope The 80mm ED does not come with a finder scope, diagonal or eyepieces in order to grant the user the greatest versatility in customizing the instrument to suit their tastes. [. . . ] The Crayford design allows for smooth, precise focusing without any image shift that typical rack-and-pinion designs experience. If you find that the focus wheels are too tight or too loose, you can make adjustments to the focuser tension by using the focuser tension thumbscrew located on the bottom of the optical tube, between the focus wheels. Make adjustments to this thumbscrew until the focuser motion feels comfortable. Please note that you must have at least some tension applied to the focuser drawtube or else it will not move when you turn the focus wheels. Calculating Magnification (Power) It is desirable to have a range of eyepieces of different focal lengths, to allow viewing over a range of magnifications. To calculate the magnification, or power, of a telescope, simply divide the focal length of the telescope by the focal length of the eyepiece: Telescope F. L. = Magnification For example, the 80mm ED, which has a focal length of 600mm, used in combination with a 25mm eyepiece, yields a power of 600 ÷ 25 = 24x. Every telescope has a useful limit of power of about 45x-60x per inch of aperture. Claims of higher power by some telescope manufacturers are a misleading advertising gimmick and should be dismissed. Keep in mind that at higher powers, an image will always be dimmer and less sharp (this is a fundamental law of optics). The steadiness of the air (the "seeing") will limit how much magnification an image can tolerate. Always start viewing with your lowest-power (longest focal length) eyepiece in the telescope. After you have located and looked at the object with it, you can try switching to a higherpower eyepiece to ferret out more detail, if atmospheric conditions permit. If the image you see is not crisp and steady, reduce the magnification by switching to a longer-focal-length eyepiece. As a general rule, a small but well-resolved image will show more detail and provide a more enjoyable view than a dim and fuzzy, overmagnified image. Note About Chromatic Aberration Chromatic aberration literally means color distortion. Whenever light passes through one material to another, light of different wavelengths (color) is bent by different amounts. This is a problem that plagues refractor-type telescopes, since light passes through both air and glass to form an image. Most astronomical objects emit a spectrum comprised of many different wavelengths of light, so each wavelength will be bent by a slightly different amount when passing through a lens. This results in each color of light reaching precise focus at a slightly different point, which reduces image sharpness. The objective lens comprises two individual lens elements, one of which is made of "ED" (Extra-low Dispersion) glass, a special type of glass that has superior refractive properties compared to normal types of glass. The use of this ED glass minimizes the amount of chromatic aberration, resulting in a cleaner, sharper image compared to that in standard achromatic telescopes. Photography with the 80mm ED Refractor With an optional camera adapter, the 80mm f/7. 5 ED becomes a 600mm f/7. 5 telephoto lens for a single-lens reflex camera. [. . . ] Never reuse tissues. 2 Specifications Optical tube: Seamless aluminum Objective lens diameter: 80mm (3. 1") Objective lens: Achromatic, rear element made of ED glass, air-spaced Objective lens coating: Fully multi-coated Lens cell: Machined aluminum Focal length: 600mm Focal ratio: f/7. 5 Focuser: Crayford, accepts 1. 25" or 2" accessories and camera T-Ring Mounting: 1/4"-20 mounting block, optional tube rings Weight: 5 lbs. Length: 23. 5" 3 One-Year Limited Warranty This 80mm f/7. 5 ED Refractor is warranted against defects in materials or workmanship for a period of one year from the date of purchase. This warranty is for the benefit of the original retail purchaser only. During this warranty period Orion Telescopes & Binoculars will repair or replace, at Orion's option, any warranted instrument that proves to be defective, provided it is returned postage paid to: Orion Warranty Repair, 89 Hangar Way, Watsonville, CA 95076. [. . . ]