Pupillary magnification is just the size of the exit pupil divided by the size of the entrance pupil. This ratio is often left out of optics equations as it generally only has a mild effect on the numbers. It is also, for the most part, only useful with macro and close-up photography. The specifics of which will be discussed in later installments.
As mentioned in the previous section, lenses of retrofocus and telephoto design will tend to have asymmetric pupils. To translate this into pupillary mangificatiob results in telephoto lenses having a pupillary magnification P<<1. Retrofocus lenses will tend to have P>>1. Symmetric lenses will tend to hover in the range of 1.
Entrance pupil
Exit pupil
The above lens (Nikon 200/4 micro) has a large entrance pupil and a small exit pupil and it istherefore a telephoto design. The pupillary magnification is about 0.5.
The lens shown two posts ago,a 28mm lens wide-angle,is a retrofocus lens and has a P of about 2.