Object telecentric system: It is often used in the measuring microscope. Its effect is to eliminate the measuring error caused by the position errors of the image plane.
Depth of Field: the distance between the farthest and the nearest object planes which can still be formed clearly on the image plane. The size of the acceptable blur is a subjective concept.
2. Selection of Image Rays in Microscope and Telecentric System .
P121
Telecentric System
Object telecentric system: The aperture stop is on the second focal plane; the entrance pupil is at infinity.
D0 C0 B0 A0 A
B C D
Exit pupil Exit window
The vignetting will increase as the field angle of view increases. Effect of the vignetting: If a system has the vignetting, there will be a transition area in the image plane, changing from bright to dim, without a clear borderline. Reducing the vignetting: The field stop must coincide with or be near the real image plane of the system.