Читать книгу Optical Engineering Science - Stephen Rolt - Страница 16

Where an image or object is located at infinity, all rays emerging from or travelling to these locations will be parallel with respect to each other. In this instance, the point located at infinity is said to be at an infinite conjugate. The corresponding conjugate point to the infinite conjugate is known as a focal point. There are two focal points. The first focal point is located in the object space with the corresponding image located at the infinite conjugate. The second focal point is located in the image space with the object placed at the infinite conjugate. Figure 1.6 depicts the first focal point:

Figure 1.6 Location of first focal point.

As well as focal points, there are two corresponding focal planes. The two focal planes are planes perpendicular to the optical axis that contain the relevant focal point. For all points lying on the relevant focal plane, the conjugate point will lie at the infinite conjugate. In other words, all rays will be parallel with respect to each other. In general, the rays will not be parallel to the optic axis. This would only be the case for a conjugate point lying on the optical axis.