Question

Find the position and size of the entrance and exit pupil of
human eye. Assume pupil diameter as 3 mm.​

Answer 1

Answer:

Entrance Pupil

We first consider the effects of apertures at multiple positions in the beam path on the opening angle. We assume an imaging system which is focused to some object plane, and we consider rays starting from the center of the object plane. It is important to realize, however, that their effects are not the same for rays starting from a different (off-axis) location in the object plane. Therefore, it is not sufficient to know the maximum opening angle only.

imaging system with aperture

The entrance pupil is the apparent aperture as seen from the object side.

One solves that problem by constructing the so-called entrance pupil, which has a certain diameter and axial position. In That aperture is imaged to the left side, i.e., considering only the optical elements left of it. The rays on the object side can then be protected back to find the edge of the entrance pupil – in this case a virtual image well behind the first and even second optical surface. The entrance pupil is the apparent aperture as seen from the object side.

construction of entrance pupil

For an aperture in front of other optical elements, such as A1 the entrance pupil is identical with that physical aperture. The construction of the entrance pupil for aperture A3 in Figure 1 would again lead to a different result. Indeed, those three apertures would also have different optical effects on the system performance.

In case of a single thin lens of limited size, and no additional apertures, the entrance pupil would simply be the transparent part of the lens. For a multi-lens system, the entrance aperture can be located before, within or after the optical setup.

For any photographic objective, for example, one can construct the position and diameter of the entrance pupil based on the optical design. In case of multiple apertures, the one causing the strongest limitation of light rays is considered. One can then specify those entrance pupil parameters instead of all the details of actual physical apertures and other optical elements; with those data only, the aperturing effects for the object side are sufficiently specified.

For a zoom lens, the entrance pupil generally depends on the zoom setting.

The opening of a photographic objective is usually specified with the f-number, which is defined as the ratio of focal length and diameter of the entrance pupil.

The axial location of the entrance pupil is also relevant as the camera's center of perspective.

For an objective which is telecentric with respect to object space, the entrance pupil lies at infinite distance from the objective. That leads to an orthographic view, i.e., with a magnification which is independent of the object distance.

For a microscope objective, the entrance pupil together with the focal length is directly related to the numerical aperture, which is the usual specification.

Some authors use the term entrance pupil for what should actually be called the diameter of the entrance pupil; note that the axial position of the entrance pupil is also an important parameter.