Fisheye lens
About fisheye lens
Fisheye lenses are an acquired taste. They are best used in small doses, but they give a unique perspective on things. The Canon 15mm fisheye is quite expensive (around $600) so doesn't really make sense for a lens you may not use much. However there is an alternative if you don't mind manual focus and manual aperture setting. Focus really isn't much of an issue as the depth of field is so large with such a short focal length lens.
.Fisheye lenses "distort" the image. Lines which run through the center of the field remain straight, but lines near the top of the frame or the sides of the frame bow outwards. Used carefully the fisheye effect isn't overpowering, so for example, if you put the horizon across the middle of the frame it remains straight. However if you put the horizon near the top or bottom of the frame it will curve severely. Too many highly distorted images soon leave the viewer looking for something else, but used carefully a fisheye can give a unique wideangle perspective without forcing too many optical distortions on the viewer.
Majid Naghi photographer ( +98 912 204 3001 )
The lens comes with red, yellow and green filters which screw on to the rear of the lens and a small carrying pouch (or at least mine did). It looks like a well built lens, the focusing is smooth and the aperture click stops work fine. The glass and coating in mine look excellent and the lens has a built in "hood", if you can call a 15mm fisheye hood a hood. It's more of a slight extension of the barrel on the top and bottom. Since the front element bulges out so far, you can't use front mounted filters and since the diagonal coverage is 180 degrees you can't just hold a filter in front of the lens either without getting it in the shot!
On the conventional film camera, a lens with 14-mm focal length, known as a fisheye lens, creates a hemispherical field of view. This dramatic view has severe geometric distortion in which the horizon appears strongly curved. Such images cannot be utilized for measurement or mapping purposes, but do provide a broad field of view for reconnaissance of landscapes.
Fisheye camera lens
In photography, a fisheye lens is a wide angle lens that takes in an extremely wide, hemispherical image. Originally developed for use in meteorology and astronomy and called "whole-sky lenses", fisheye lenses quickly became popular in general photography for their unique, distorted appearance. They are often used by photographers shooting broad landscapes to suggest the curve of the Earth. hemiispherical photography is used for various scientific purposes to study plant canopy geometry and to calculate near-ground solar radiation.
The focal leghts of fisheye lenses depend on the film format. For the popular 35 mm film format, typical focal lengths of fisheye lenses are between 8 mm and 10 mm for circular lenses, and 15-16 mm for full-frame lenses.
In the past, fisheye photography had been considered primarily a ``special effect'' to be used sparingly for its ability to provide a distorted perspective. However, fisheye imaging recently has become of much greater importance. There are two major reasons:
- The ability to ``see everything'' using a single camera. For security and surveillance applications, the wide field of view possible with fisheye lenses makes it much easier to cover an area. The fact that a fixed sensor resolution with a wide field of view means details are less visible is not much of a problem - if necessary, a second camera with pan, tilt, and zoom capabilities can be guided to image the critical detail areas based on the fisheye image. Further, the short focal length of a fisheye lens means that there is great depth of field even at F numbers that facilitate low-light imaging; pretty much everything can be in focus simultaneously.
- The availability of digital processing to ``undistort'' the fisheye image. This makes fisheye lenses very useful as alternatives to naturally rectilinear ultra-wide-angle lenses even for creating high-quality images. Further, since the digital processing is not really ``undistorting,'' but converting between different types of projections, the wide field of view of fisheye lenses means fewer images must be stitched to make projections like 360 degree virtual tours.
Fisheye lenses and adapters do not have a fixed entrance pupil (no-parallax point), as most rectilinear lenses do. Instead, the entrance pupil of a fisheye lens depends on the angle from the lens axis, typically moving forward as the angle increases from 0 degrees to 90 degrees.
In theory, this means that it is impossible to get a perfectly stitched panorama from a fisheye lens.
In practice, stitching can be almost perfect if you calibrate your camera mount using the same angle from lens axis that you usually use for stitching.
Commercially Available Fisheye Lenses
For film and digital cameras alike, fisheye lenses tend to be expensive niche-market items. In this technical report, we will limit ourselves to alternatives that are truly fisheye lenses, as opposed to things like photographing reflections in convex mirrors (which will be the topic of another technical report). The fisheye lens options fall into just a few general categories:
Camera Choices For The Peephole Fisheye Converter
A peephole fisheye can be used as a converter lens on any of a wide range of cameras. Of course, that does not mean it will work on every camera and, in fact, it doesn't work on most. Usually the problem is a standard lens that either has a front element with too large a diameter or has focal properties that prevent the peephole fisheye converter from producing a good image. The first problem is usually obvious from camera specifications on the web, but the second is very difficult to determine without physically testing the camera. Ironically, slightly longer focal length lenses tend to work better because they give a larger fisheye image.
Fisheye Lens with 180º Frame Filling Field of View
This full frame fisheye lens has a 180º field of view diagonally to the Four Thirds image sensor, and a focal length of 8mm (equivalent to 16mm in a 35mm camera). Because of this it can be used to create extremely dramatic photographic images that cannot be seen unaided with the human eye. These images include humorous representations of the subject using extreme barrel distortion, or images with exaggerated perspective and extremely great depth of focus. Because this lens is specifically designed for digital cameras and conforms to the “Four Thirds System,” it will provide reliable photographic performance even at the edges of the images.
There are a small number of ~180 degree circular fisheye converter lenses. OLYMPUS and NIKON both have produced moderately-priced high-quality converter lenses for their digital cameras, and companies like IPIX also have offered combinations like a NIKON FC-E9 fisheye converter fitted to a CANON G6 in support of making immersive virtual tours. The NIKON converter sells for ~$250, but adapters are cheaply available for only a few cameras. Thus, the RAYNOX DCR-CF185PRO 185 degree circular fisheye is probably the cheapest high-quality converter that works on a wide range of digital cameras, selling at a price of ~$370. The RAYNOX, NIKON, and FIT (OLYMPUS) fisheyes are shown left-to-right in Figure 2, with our alternative fisheye at the right edge. Another alternative, although not directly a digital one, would be to purchase one of the analog peephole video cameras. These cost ~$100 (~$150 with power supply) and claim to provide a 170 degree monochrome view with 0.05 LUX sensitivity. Of course, one additionally needs a video digitizer. Finally, SWANN makes an ``up to 150 degree'' fisheye lens, the SW-P-FLBLIv2, for their 12mm PC board and miniature cameras. It sells for ~$25. At least in theory, this lens should be able to be fitted to a webcam in place of its normal lens. There are, however, various issues involving the sensor size (both 1/3 and 1/4 inch sensors are common) and the critical alignment of the lens mount so the focal plane falls on the sensor.
A New Use For Door Peephole Viewers
There is a commodity market for a specific type of fisheye lens: door peepholes. Door peepholes were not designed to be camera lenses, however, most devices for human viewing are designed to produce their images at an apparent viewing distance comfortable for humans - which is a fair approximation to what a converter lens does. Thus, it should be possible to use a door peephole as a converter lens. Converter lenses avoid the problems involving sensor size and critical alignment of the focal plane, and they can be literally taped or hot-glued onto nearly any base lens.
Fisheye Lens with 180º Frame Filling Field of View
This full frame fisheye lens has a 180º field of view diagonally to the Four Thirds image sensor, and a focal length of 8mm (equivalent to 16mm in a 35mm camera). Because of this it can be used to create extremely dramatic photographic images that cannot be seen unaided with the human eye. These images include humorous representations of the subject using extreme barrel distortion, or images with exaggerated perspective and extremely great depth of focus. Because this lens is specifically designed for digital cameras and conforms to the “Four Thirds System,” it will provide reliable photographic performance even at the edges of the images.
Sony DSC-F828
The SONY DSC-F828 is a serious 8MP machine with a zoom lens spanning the 35mm equivalent of 28mm to 200mm; thus, it makes a good vehicle for testing the ``mount a peephole in a zoom lens lenscap'' concept so often discussed for conventional SLRs. The peephole fisheye is not effective with this SONY. The primary problem is the large front element of the lens; the image circle is either too small or vignetting is a problem.
