Optics Definitions

Minimum Working Distance

The minimum distance from the object plane to the front of the lens (e.g. How close can the lens come to the object?)

Maximum Working Distance

The maximum distance from the object plane to the front of the lens (e.g. How far can the lens be placed away from the object? Is there a physical constraint in the operating space?)

Total Optical Path Length

The total distance from the object plane to the image plane.

Minimum Acceptable Feature Size

Smallest feature size which must be resolved by the imaging system (including the camera and the lens). If for example a system is examining a 10 element bar code with each code being 1 millimeter in width, then conservatively the system must be able to resolve at least 0.5 mm.

Camera Pixel Size

Most CCD and CMOS imagers consist of picture elements dubbed "pixels". Each pixel is one sensor within the array and has a definite size which should be available by the manufacturer. Sizes typically range from 8-20 microns. This can also be calculated by knowing the overall size of the array and the number of horizontal and vertical TV lines. Refer to your manufacturers data sheet for more information.

Depth of Field

The maximum depth over which the lens maintains an acceptable level of focus. If for example you were looking at an item which varies over time (such as an assembly line), will the object always be at the working distance precisely or will it tend to move farther or nearer over time to the lens/camera combination? The idea here is that the lens should be designed with a given depth in mind.

Field of View

In terms of angle or object size, what is the total necessary coverage of the lens. In other words are you looking at a 3 ft x 2 ft object 20 feet away? Do you require a 20 degree coverage regardless of distance? Have you allowed for the size of the object, the location of external references and variations in part location?

Chief Ray

In a photographic system, the chief ray passes through the optical axis at the center of the optical system. In a telecentric system the chief ray intersects the optical axis at the exit pupil.

Spectrum

What wavelengths of light must the system image? Will the product be used for holiday photos (visible - achromatic) or for avoiding collisions on foggy shorelines? (infrared) In machine vision, will the object be illuminated with white light, with LEDs or with lasers?