LanguagesLenses: Fisheye lenses
Camera lenses have what is called an 'angle of view', which is the limit of within which the subject can be photographed in accordance with the focal length and the imaging format, similar to human vision. The angle of view of standard lenses, which is thought to be near that of the human eye, is approximately 50º, while that of a 15mm fisheye lens is 180º (diagonally across the frame in the 35mm format). This means that almost everything that is in front of the camera is included in photographs taken by fisheye lenses – the sky above, the ground below and the surrounding scene on the left and right. To see 180º with a human eye will normally require you to turn your head and therefore, unlike the angle of view of a fisheye lens, is not visible in normal vision.
The Canon EF8-15mm f/4L Fisheye USM zoom was the world's first fisheye zoom lens to offer both circular and full frame images.
Because fisheye lenses put everything within an angle of view of 180º onto an image sensor, or film, there is much distortion around the edges of the photograph. All straight lines out side of the centre of the photograph become curved. The stronger the hyperfocal effect, which puts everything in the picture into focus, the larger the objects at the centre appear. Meanwhile, objects near the edges of the frame are extremely warped, creating a tremendous feeling of perspective.
The name 'fisheye' was first applied to this type of lens because this is how a fish underwater sees the outside world when it looks up, an effect that's related to the ratio of the refraction of light. Used skilfully this type of lens can open up unique, creative vistas as well as being able to act as an ultra wideangle lens, thanks to the fact that the lines in the centre of the image are not deformed.
In late 2010, Canon updated one of the longest standing EOS-compatible lenses, the EF15mm f/2.8 Fisheye, with the EF8-15mm F/4L Fisheye USM zoom lens. The zoom lens takes all the benefits of the original fisheye lens and improves on them in every area, as well as adding the versatility of a zoom lens. The EF8-15mm f/4L Fisheye USM provides the ability to be both a full frame fisheye or a circular fisheye lens.
Circular fisheye
Circular fisheye is the classic fisheye view - the lens projects a circular image back to the sensor so the edges of the frame are black in the corners - no light reaches them. It has uses both in science and for creative images. With the EF8-15mm f/4L Fisheye USM lens, this is only possible on full frame cameras, such as the EOS 5D Mark II and EOS-1Ds Mark III DSLRs. On the smaller sensor EOS DSLR cameras, those with APS-H or APS-C sensors, the field of view of the sensor is narrower and therefore you cannot achieve the full circular effect.
When using the lens as a circular fisheye, the field of view is fully 180º horizontally, vertically and diagonally.
Full frame fisheye
Full frame fisheye takes the 180º view but only applies it to the diagonal field of view because to be full frame with no circle, the field of view in the horizontal and vertical axes can't capture a full 180º.
Full frame is more widely used photographically because many people feel it gives a more aesthetically pleasing result.
The lens works as a full frame fisheye on all three sensor size cameras in the EOS DSLR range – full frame, APS-H and APS-C - although on the smaller sensors, a little of the field of view is lost due to the sensor size.
