Entrance pupil, lens

The entrance pupil is nothing more than the area of a lens that accepts radiation and defines the relative useful portion of the lens. Since a coherent source is a point source (zero diameter), the image in the entrance pupil will also have zero diameter and thus incoherent source is rigorously a source of infinite extent (a = >) and is only of academic interest since all light collected from any real source is always imaged within the entrance pupil, so that c is always <1. In practice, partially coherent sources are used. 

In this equation, n is the refractive index of the imaging medium and 6 is the angular aperture, the apparent angle of the lens apeiTure as seen from the focal point. The human eye has an entrance pupil of 7 mm and an NA value of 0.002. Thus, by Eq. 2.1, the human eye can resolve two objects, at a normal viewing distance and when the objects are... 

The illumination system comprises a series of relay optics and uniformizing optics that project the radiation from the source through the photomask to the entrance pupil of the projection optics of the lithographic lens, where it forms an image of the illumination source (see Fig. 13.8). This type of illumination system is referred to as Kohler illumination. The fraction of the pupil filled by the illuminator source s image determines the degree of coherence in the projection... 

Depth of focus increases with smaller apertures. For distant subjects (beyond macro range), depth of focus is relatively insensitive to focal lengfh and subject distance for a fixed / number (defined as fhe ratio of the focal length of the lens to the diameter of its entrance pupil). In the macro region, depth of focus increases with longer focal lengfh or closer subject distance, while depth of field decreases. 

The values of Op, Oq, and Op can be determined by numerical methods for a given set of system parameters from Eq. (12). However, it should be noted that there is an upper physical limit on these angles caused by a finite size of the entrance pupil of the lens. This maximum entrance pupil can be found from the NA of the lens and the focal length, /. It can be shown that this limiting angle, 0 can be calculated by solving... 

The cornea is the outer entrance to the eye. The iris is controlled by muscles so as to adjust the pupil of the eye according to ambient light intensity. The lens focuses light upon the retina and its shape can be somewhat altered by musculature control. The retina consists basically of a mosaic of light-sensitive cells, each operating on a photo-chemical principle. There are two (2) types present the "rods" and the "cones . The basic difference between the two is that cones are sensitive to color whereas rods have little color response and are operative primarily when... 

---