The Objectives – The Fisheye
The Fisheye Lenses, some already mentioned in the article on wide-angle lenses, are an extreme wide-angle lenses themselves. Their focal length is by far the shortest and varies between 6 and 16mm. Consequently, the viewing angle part by 180 ° in order to cover angles even greater when we use the very short focal length lenses (6 °). In these cases, however, the lens tends to be particularly cumbersome (see second photo) both as regards the overall size of the lens that the front protuberance (necessary both to overcome the limit of 180 °).
The fisheye obviously the extreme ones that are the defects of the wide-angle barrel distortion in particular this is not just mentioned but it is the raison d’être of a fisheye lens akusaraprosound. In all the pictures taken with these objectives you will not find in fact never a straight line pleasant when it passes exactly through the center. In addition to the internal lines to the photo, they are also to be strongly curved contours of photography, which is why many fisheye photos are round instead of rectangular.
Fisheye lenses there are two types circular and full frame. The circular fisheye round produce an image, capturing everything that is in visual range. The full frame fisheye instead carry a crop (crop) circular image by returning a photograph in traditional format (rectangular).
And here are the results of two photographs the first one has the convergence of lines and the second lines are almost perfectly parallel.
A comparison we can see it between a Nikkor 500 and a traditional 18mm (original here). In the circle it is displayed photographed area with the catadioptric.
Beware of filters since the first optical element of a fisheye lens is spherical and leans heavily on the objective body, it is impossible to use normal threaded filters. Many fisheye, to overcome this problem, include inside of color filters or neutral density or a slot within which thread of the filters (usually of plastic or slides).
T it term fisheye (simply translated in fish eye) is due to the fact that a fish underwater is capable of displaying a hemisphere. The term was coined by Robert W. Wood in his book Physical Optics.
The first fisheye lens is signed Robin Hill and her name was Robin Hill Sky. It was built to display on paper cloud formations and produced on a plate image of the entire sky.