Constant Magnification

Everyday experience teaches that conventional lenses see an object as being larger if it is close and smaller if it is far. This is part of how we judge distance by eye.

For automatic gauging applications, however, this property can introduce significant errors. For example, bottles on conveyors can "walk" side to side between the rails, thus changing their distance to the camera that is viewing them.

 The difference might seem small, but when trying to measure objects to within a few thousandth of an inch, the difference can be critical.

Good telecentric lenses overcome this problem. How far an object can change its distance and still appear to be the same size is called magnification depth of field. This is different from image sharpness depth of field, which is the commonly understood meaning of "depth of field."

Large magnification depth of field means that telecentric lenses are ideal for a great variety of dimensional-gauging applications. Some typical examples include threaded fasteners, machined parts, bottle geometry, and PCB component placement, or any time you want to measure something with little or no perspective error, or with varying distance.