■ Magnification The ratio of the size of a magnified object image created by an optical system to that of the object. Magnification commonly refers to lateral magnification although it can mean lateral, vertical, or angular magnification. ■ Principal Ray A ray considered to be emitted from an object point off the optical axis and passing through the center of an aperture diaphragm in a lens system. ■ Aperture Diaphragm An adjustable circular aperture which controls the amount of light passing through a lens system. It is also referred to as an aperture stop and its size affects image brightness and depth of focus.
■ Field number (FN), real field of view, and monitor display magnification unit: mm The observation range of the sample surface is determined by the diameter of the eyepiece’s field stop. The value of this diameter in mil- limeters is called the field number (FN). In contrast, the real field of view is the range on the workpiece surface when actually magnified and observed with the objective lens. The real field of view can be calculated with the following formula: (1) The range of the workpiece that can be observed with the microscope (diameter)
Real field of view = FN of eyepiece Objective lens magnification Example: The real field of view of a 1X lens is 24 = 24 1 The real field of view of a 10X lens is 2.4 = 24 10 (2) Monitor observation range
■ Field Stop A stop which controls the field of view in an optical instrument.
The size of the camera image sensor (diagonal length) Objective lens magnification
Monitor observation range =
• Size of image sensor Format
Diagonal length
Length
Height
■ Telecentric System An optical system where the light rays are parallel to the optical axis in object and/or image space. This means that magnification is nearly constant over a range of working distances, therefore, almost eliminating perspective error. ■ Erect Image An image in which the orientations of left, right, top, bottom and moving directions are the same as those of a workpiece on the workstage.
6.0 8.0
4.8 6.4 8.8
3.6 4.8 6.6
1/3” 1/2” 2/3”
11.0
(3) Monitor display magnification Monitor display magnification = Objective lens magnification x
Display diagonal length on the monitor Diagonal length of camera image sensor
I-40
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