Optics

Error-free depiction of the field of view

Image circle diameter

Even with the same lens mount Industrial cameras such as Nikon bayonet or C-mount, lenses can have different image circle diameters. This refers to the area of the sensor that can be uniformly exposed by the lens without significant shading at the edges.

Like the sensor size, the image circle of a lens is often specified in (tube camera equivalent) inches. For example, a 1/3' C-mount lens can expose a sensor size of 1/3'. It therefore covers the sensor completely. If this lens were used on a 1/2' sensor, the outer edges of the image would be darkened and the image would be "vignetted".

The image circle diameter of the lens must therefore be greater than or equal to that of the sensor!

But what happens if a 2/3' or 1' lens with the same focal length is attached to a 1/3' or 1/2' sensor? In principle, hardly anything: working distances, focal lengths, etc. do not change. Only the angle of view of the lens changes.

Calculation of the image circle diameter

In the case of an area sensor, the required image circle is ultimately the diagonal of the sensor:

Image circle diameter

With a line scan camera, there is nothing to calculate: the required image circle diameter is equal to the length of the sensor.

Calculations for sensor size, image circle diameter and required line pairs/mm (Lp/mm) can be found in the Service section of the homepage.

Important for Machine Vision

In fact, a larger image circle is generally recommended, as optical aberrations increase significantly from the centre to the edges of the image. If the lens is able to cover a larger image circle, resolution and sharpness can be improved, especially in the peripheral areas.
The intentional reduction of the optical path is achieved by the aperture of the lens. Stopping down again improves the image, as light rays near the edges are also avoided by the lenses.

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Optiken Industrielle Bildverarbeitung