equivalent focal length


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equivalent focal length

[i′kwiv·ə·lənt ′fō·kəl ‚leŋkth]
(optics)
The focal length of a thin lens which forms images that most nearly duplicate those of a given compound lens, thick lens, or system of lenses.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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MAGEE ALL-SPHERICAL NEWTONIAN REFLECTOR (All dimensions are in inches) Component Diam- Radius of Following eter curvature thickness Primary mirror 6.0 -72.00 ([R.sub.1]) 30.42 Flint lens 1.0 7.11 ([R.sub.2]) 0.10 (SF-12 glass) 4.05 ([R.sub.3]) 0.00 Crown lens 1.0 4.05 ([R.sub.4]) 0.10 (BK-7 glass) flat ([R.sub.5]) 0.00 Prism 1.0 flat ([R.sub.6]) 1.00 (BK-7 glass) flat ([R.sub.7]) 7.54 Equivalent focal length: 53.7 inches Radii of curvature are positive if convex to the sky, negative if concave.
A short Newtonian with a spherical mirror

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