Archived posting to the Leica Users Group, 1999/05/31
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Dan P wrote: >Now- my next question- since I haven't had trig since college 30 years ago, >but is the Sin 4th law the same principle as what I learned as the Cosine >law- that light falls off as a function of the cosine of the angle from the >optical axis- as the angle increases, the light diminishes by a factor of >the cosine of that angle? Yes, of course. I was a bit too sloppy, and therefore it came out wrong. In a 'standard' construction lens the light intensity falling on any area of the image plane that is off axis is reduced by the factor of cosine theta to the fourth power, where theta is is angle between the light ray and the axis. Actually this holds for more complex lenses with no distortion as well, but then you get into rear nodal point location, which isn't simple anymore. * Henning J. Wulff /|\ Wulff Photography & Design /###\ mailto:henningw@archiphoto.com |[ ]| http://www.archiphoto.com