Image circle

The image circle is a term used in photography. He describes those area that a lens able to be imaged without being by vignetting ( vignetting ) impaired or other aberrations. The image circle must be at least as large as the film or sensor format. In particular, professional cameras, or tilt and shift lenses require particularly large image circles to allow extensive adjustment.

Calculation

The minimum required image circle diameter of a lens is calculated as the diagonal of the negative or rectangular sensor according to the formula

It should be noted that even within the image circle, the aberrations usually increase toward the edge, so most lenses deliver the best quality at the image center. Also, a small amount of vignetting is often tolerated to the edge.

In photography with professional cameras therefore means taking a wide angle lens, a lens with large image circle as possible.

Land use and sensor format

Usually, sensors and films are rectangular, the lenses however provide a circular image. Taking a film or sensor whose diagonal corresponds exactly to the image circle, so it can be stated that only part of the picture that provides the lens is actually recorded by the sensor or film.

This ratio can be on the side lengths of the rectangular sensor ( a, b) calculate and set to the area of the image circle to the ratio, the lens has to deliver at least, not to vignette:

This suggests that a sensor in 3:2 format (small image film, full frame, APS formats ) the area shown in the image circle from the lens can be exploited in the best case to about 59%, a sensor in 4:3 format ( used of the most compact digital cameras) to about 61% ( 16:9: only about 54 %) and a square film or sensor area (eg 6 × 6 film ) geometrically ideal with a use of approximately 64 % would be.

• Photography