Machine Vision Systems

Lens Basics

Structure

A lens gathers light from an object, which forms an image on the CCD. The unit includes multiple lenses and aperture and focus adjustment mechanisms.

Focus

The focus needs to be adjusted according to the distance to the object, using a rolling mechanism in front of the lens. The figures on the lens show the rough focal distance and the minimum figure indicates the shortest focal distance using a single lens.

Aperture

The aperture adjustment mechanism is located behind the focus adjustment mechanism and is used to adjust brightness. The figures on the side of the lens are called F values and they signify the light-gathering power of the lens. Aperture is basically the lens diaphragm opening inside the camera lens. The smaller this value, the wider the aperture is opened and the greater the light-gathering power. The letter "C" in the F value stands for "close" and it indicates that the aperture is totally closed.

Focal Distance

Focal distance determines the scope of the visual field. With a normal lens, as the distance between the camera and the object (Working Distance) increases the visual field becomes wider. Visual field is determined by the focal distance of the lens. The focal distance is the distance from the lens to the object. A short focal distance will result in a wide visual field. In contrast, a lens with a long focal distance can be used to enlarge distant images.

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