 Conversion of f/# and NA

 
The fnumber (f/#) and numerical aperture (NA) are calculated as defined. This calc converts between them, and also gives the angle (α) of collection for the lens. The fnumber is defined in air, but for the NA, refractive index is taken into account if necessary.
 
Fill in either the f/# or the NA. The calc will provide the conversion as well as give the angle α. If you fill in both inputs, then both will be converted.  