Lens optics depend on many variables, and ALWAYS vary slightly between each individual camera model. Due to the physical nature of lens optics, lens field of view numbers need to be considered accurate to within a few degrees and therefore a few feet / meters as well. They are only intended as approximate guidelines to help select the appropriate lens, while each camera in fact has its own unique field of view with each specific lens. In addition, C- and CS-mount lenses typically deliver a slightly narrower field of view than our comparable board lenses.

In addition, lenses wider than roughly 5mm produce "artificially" wider fields of view than more telephoto lenses. In order to do so, the video image is slightly curved at the edges of the screen. While this artificial distortion is nominal for focal lengths between 4.3 and 3.6mm, curvature increases with wider angle lenses.

Be extremely wary of online lens calculators! Many produce inaccurate angle measures for all given focal lengths, and are therefore completely misleading. Also, most 1/4" CCD cameras produce a significantly narrower field of view with the same focal length lens.