At 10:13 AM 1/7/99 +1000, you wrote:
>"Rand E. Tomcala" <rtomcala@xxxxxxxxxxx> moved upon the face of the 'Net
and spake thusly:
>
>> Paul,
>> Is there an easy way to figure the angle of view for lens of less than
>> 50mm. Is there a table somewhere on the internet. Case in point, I
>> have a 17mm standard view lens, what is the angle of view and how would
>
>For a non-fisheye, angle of view is
>
> 2 * arctangent ( film-dimension / ( f * 2 ) )
>
>eg. for 50mm
>
> 2 * atan ( 43.2 / 100 ) = 46.72 degrees (on the diagonal)
>
>Remember to keep your units the same--millimetres or metres or
>whatever, and beware that many programming languages and calculators
>give inverse trigonometric results in radians, not degrees. Multiply
>by ( 180 / pi ) to convert radians to degrees.
>
>Extreme wide-angle lenses do such varied trickery that this formula
>breaks down, and field of view is best determined experimentally (or
>by RTFM).
>
>Chris.
For small x, atan(x) ~ x, so
angle = 2 * (180/pi) * atan( 43.3 / (f * 2) ) with radians to deg conversion
= 2 * (180/pi) * 43.3 / (f * 2)
~ 180 * 43.3 / (f * pi)
~ 2400 / f
which breaks down below f = 50mm. An 18mm is 100deg.
Paul Farrar
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