Angular aperture

As an opening angle of a convergent lens or a lens ( generally a focal optical system ), the angle is designated, the forms a point on the optical axis with the diameter of the entrance and exit pupil.

Specifically, we distinguish between object-side and image-side opening angle

Object-side opening angle

Image-side opening angle

The image-side opening angle determines the size of the blur circles, thus influencing the imaging depth.

Opening angle of a convex lens

In photographic lenses, the positions of the entrance and exit pupil is usually no longer correspond to the position of the principal planes, their diameter is usually variable. In contrast to lenses that are contained additional aperture and usually constructed from several lenses fall at a converging lens entrance and exit pupil in the center of the lens together - their diameter simply corresponds to the lens diameter. Thus, the distance of the object point to the entrance pupil of the object width and the distance of the image point corresponding to the exit pupil corresponding to the image distance. Thus, the conditions are simplified so that the opening angle can be easily calculated at a converging lens:

For the object-side opening angle and

For the frame opening angle

Large object distance

A further simplification is obtained when the opening angle for very large object distances ( "infinity" ) is considered. Grows the object distance beyond all limits, it is

According to the lens equation, the image width corresponds to infinitely large object distance of the focal length f, that is