| Table 1: Types of format utilization |
| circular | trimmed circle | Full format |
| circular | cropped circle | full frame |
| 
| 
| 
|
| 3:2 | 52 % Sensor | 78 % field of view, 92 % sensor | 59 % Image field |
| 4:3 | 59 % Sensor | 86 % field of view, 90 % sensor | 61 % Image field |
| 
Circular fisheye for the 35 mm format
| 
Full frame fisheye with rudimentary lens hood
|
| 
Recording with circular fisheye
| 
35 mm circular fisheye on DX format camera
| 
Interior photographed
with full frame fisheye
|
Fisheye lenses are distinguished on the one hand according to their projection type (see imaging functions below) and on the other hand according to their image circle diameter in relation to the recording format.
Circular
Fisheye lenses whose image circle diameter is (at most) as large as the shorter edge of the recording format of the camera are called circular fisheye (also "circular image fisheye" or "round image fisheye") because they design a circular image within the rectangular recording format. The image circle of the lens is used 100%. In plate 1 the maximum possible sensor utilization is given; it turns out to be smaller due to a practically slightly smaller image circle. In order not to cut the image circle, circular fisheyes do not have a lens hood. Circular fisheyes are the first choice when as much of the surroundings (usually a hemisphere) as possible is to be captured. The first fisheye lenses developed were circular fisheyes. Lacking a full frame fisheye, cropping a rectangular area further reduces sensor or film utilization to a maximum of 31% (3:2) or 36% (4:3) and would be conceivably awkward.
Full format
Fisheye lenses whose image circle diameter is (at least) as large as the diagonal of the camera's shooting format are called "full-format fisheye" (also "diagonal fisheye" because of the double meaning of the term "full-format" for sensor utilization or sensor size). They achieve their largest angle of view (usually 180°) only across the image diagonal; their horizontal and vertical angles of view are correspondingly smaller, and parts of the lens' field of view are not used. The sensor, on the other hand, is utilized to 100 %. The lens hood turns out to be very small, limiting the field of view to an approximately rectangular area that extends only slightly beyond the intended shooting format. As fisheyes became popular in general photography, camera manufacturers began to develop full-frame fisheyes. The rectangular format is most comfortable for direct reproduction of the original images (without conversion).
Trimmed circle
If the camera does not have the sensor format for which the fisheye lens is intended, the angle of view and format utilization change. With certain combinations, a usable field of view in the form of a cropped circle can be achieved as an intermediate format of circular and full frame. This results in good sensor utilization and usually less loss in rectangular cropping of images converted to another projection type.
Either a circular fisheye for 35mm format is used on an APS-C or DX camera, or a full-frame fisheye for DX format is used on a full-frame 35mm camera. In the second case, the lens hood crops the image and must be removed. If it is not removable, it can be shortened with a tool (shaving the lens). Some fisheye zoom lenses can also achieve a cropped circle.
Ideally, the image field is a circle cropped on two sides. The image circle diameter is then (at most) as large as the longer side of the recording format. The angle of view becomes maximum, e.g. with landscape format, at the round image edges both diagonally and horizontally; only vertically is it smaller. In practice, there is also the three-sided cropped circle when the sensor area is not centered on the image circle (e.g. area-true Sigma 8 mm fisheye [older model with aperture F/4] and camera with APS-C sensor), or the four-sided cropped circle when the imaging function creates a larger image circle (e.g. angle-linear Canon 8-15 mm fisheye at 8 mm and camera with APS-C sensor).
When converting to stereographic projection, a full-frame image with 180° diagonal angle of view can be obtained after rectangular cropping (Starting from a full-frame image, the stereographic projection would be pincushion-shaped. Rectangular cropping would remove the pincushion peaks and thus reduce the diagonal angle of view). It may be that image angles of 180° are no longer possible with the original format, but only with a wider format (e.g. 16 : 9) of the converted image.
