Maximum useful magnification ……………….. 2.0*D 156.25 compared with 100, or 1.56 times more light-recording power, where Efficiency is the efficiency of the lens for photographing an average meteor (in a meteor shower) center of the other). Width of little finger at arm’s length ……………….. 1° T is the exposure time in minutes Alpha (Polaris) ……………………. Using the same Telescope what is the magnification for each of these eyepieces? h = (D*i)/F top-quality guiding. f O = D O ×f R = 152.4 × 5 = 762 mm. 2-3x yields only a slight elongation. Lambda is the wavelength of the light in mm F is the focal length of the objective (Since visual magnification is the ratio of the objective to ocular focal length, the combination of prime-focus camera and off-axis guider with a 12.5-mm ocular gives a guiding magnification of f/12.5. Zeta …………………………………… 4.3 Magnification depends on the focal length of the telescope and the focal length of the eyepiece. The earth rotates 5′ in 20 s, which yields a barely detectable star trail with an unguided 50-mm lens. k is a constant with a value of 57.3 for Theta in degrees, 3438 in minutes of arc, 206265 for seconds of arc (the number of the respective units in a radian). F is the focal length of the lens in mm Normal high power, double stars …………….. 1.2*D to 1.6*D f is the f-number (f/) of the lens F = (D*i)/h, where i is the linear image size in mm of the image at prime focus of an objective or telephoto lens (for terrestrial objects, equal to 24 mm divided by the amount of enlargement of the print [3x is the standard for 35-mm film] for the smallest dimension of 35-mm film]) Alpha Ursae Majoris (Dubhe) to Delta Ursae Majoris (Megrez) 10° Focal length of telescope: Eyepiece: X Magnification: 1000mm: 40mm: 25x: 1000mm: 30mm: 33.3x: 1000mm: 20mm: 50x: 1000mm: 6mm: 167x . 0.0044 derives from (2*Pi)/N for minutes Magnification depends on the focal length of the telescope and the focal length of the eyepiece. 0.25*D To compare the relative light grasp of two main lenses used at the same magnification, compare the squares of their diameters. Alpha is the apparent field D is the distance of the object in km, Geographic distance of one sec of arc = 30 m * cos of the latitude, where cos(Latitude)=1 on lines of constant longitude, Penny, 4 km distant ………………………………… 1″ 206265 is the number of ” in a radian Twice this distance, or an 8-minute (480- second) apparent field angle, is a more practical value for comfortable viewing. The light uses a secondary mirror inside to reflect the light inside and so uses its size intelligently. Newtonian telescopes). size of a star disc in “) minutes of arc, 206265 for seconds of arc (the number of the respective units in a radian). Alpha Ursae Majoris (Dubhe) to Eta Ursae Majoris (Alkaid) . 2-3′ (8-12 s) is necessary for an undetectable trail, 1′ (4 s) for an expert exposure. f is the f-number (f/) of the lens, Print EFL = Camera FL * Print Enlargement, where Print EFL is the print’s effective focal length f is the focal length of the ocular In theory, a telescope could see everything with a magnification of 60x (1″ magnified to 1′). The magnification of the eyepiece depends upon its focal length and is calculated by the same equation as that of a magnifying glass (above). (Height of Big Dipper’s cup. Close doubles ………………………………………… 2.35*D S is the film’s ISO speed Thus: TELESCOPE FOCAL LENGTH / OCULAR FOCAL LENGTH = MAGNIFICATION. Focal Length is how far light travels inside the telescope before it reaches a focus point. f is the f-number (f/) of the system, Example: a 200-mm f/8 system compared with a 100-mm f/5 system This quantity also applies to the moon. Under ideal conditions, the human eye can resolve anything subtending more than a 1′ angle, i.e., see an object as an extended object or see a double star as two stars rather than a single point of light, provided that the two components are of nearly equal brightness.


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