In researching human vision for my thesis, I decided that the Leica Noctilux f/.95 lens was the best choice for the creation of my images.

Starting with focal length:

A lens with a focal length approximately equal to the diagonal size of the film or sensor format is known as a normal lens; its angle of view is similar to the angle subtended by a large-enough print viewed at a typical viewing distance of the print diagonal, which therefore yields a normal perspective when viewing the print. If the frame size is 24mm x 36mm, the diagonal is 43.267mm.

Most manufacturers market the 50mm lens as the normal lens (despite being a few mm larger) as it is the optimum focal length that has zero distortion. The problem is that a 50mm lens only affords a 46-degree field of view that is significantly less than the human field of vision – which would be closer to a 24mm lens. However, if we were to use such a wide-angle lens our images would suffer significant distortion that does not appear when using a normal lens. Our brains have the ability to compensate for this distortion – however the camera does not. Therefore the 50mm lens is considered to be optimal, due to lack of distortion.

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