In the selection process of optical lenses, it is very important to understand and calculate the magnification of the lens because it directly affects the size and detail of the image. Different types of lenses, such as telecentric lenses and fixed focus lenses, have different methods of calculating magnification.

Calculation of Magnification for Telecentric Lenses

For telecentric lenses, the calculation of the magnification is relatively straightforward and the following formula is usually used:

Magnification = chip size / field of view

• Chip Size：Refers to the size of the camera sensor (e.g. CCD or CMOS), usually in millimeters (mm). For example, common sensor sizes are 1/2 inch, 1/1.8 inch, etc. These sizes need to be converted to millimeters.

• Field of view：This refers to the size of the area that can be clearly imaged by the lens at a given working distance, also measured in millimeters. The size of the field of view determines the width or height of the image.

Calculation of Magnification for Fixed Focus Lenses

For fixed-focus lenses, the calculation of the magnification is slightly more complicated because it involves two factors: the focal length and the working distance. An approximate formula is usually used:

Chip size/field of view ≈ focal length/working distance

• Monitoring range：This is a fixed parameter of the lens that indicates the distance from the center of the lens to the imaging plane, usually measured in millimeters. The focal length determines the angle of view and imaging size of the lens.

• Working distance：This refers to the distance between the front of the lens and the subject, also in millimeters. The choice of working distance affects the sharpness of the image and the magnification.

It should be noted that this formula is an approximate formula, because in practice, the imaging of the lens is also affected by a variety of other factors, such as lens aberration, depth of field and so on.

1、telecentric lens: magnification is directly determined by the chip size and field of view.

2、fixed-focus lens: magnification can be calculated by the focal length and working distance of the approximate relationship, but need to note that this is an approximation.