Lenses

What is a fisheye lens

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Most lenses are “rectilinear,” which means they’re designed to project an image onto a flat surface (the film or the image sensor) and render straight parallel lines as straight parallel lines. This is actually a complicated optical trick, since a simple lens really wants to project an image onto a spherical surface (such as the interior of the human eyeball). It also becomes increasingly complicated to do as the field of view of the lens becomes larger, as with wide-angle lenses - one reason why really wide angle lenses are so expensive.

This type of projection onto a flat field is something that different lenses do to varying degrees of success. High quality lenses, particularly those intended for use for macro or architectural photography, do a pretty good job. But cheaper lenses will compromise on this slightly and will either barrel or pincushion somewhat. That is to say, a photograph of a square object may appear to be either bulging outwards or squashed inwards, because parallel lines are being portrayed as curved. In fact, nearly all cheap lenses tend to have barrel distortion - it’s just that people usually don’t realize it because they rarely take photos of square or rectangular objects.

 

A fisheye lens is a wide angle lens where no effort has been taken to render parallel lines as parallel. Instead, only lines which pass through the centre of the frame are straight. All other lines appear as curves, becoming increasingly curved as you near the edge of the frame. This line curvature has the effect of making near objects seem closer and more distant objects seem further off, as they fall away. If you’ve ever looked through the glass peephole viewers in a door then you know the effect.

Sometimes people call rectilinear lenses “corrected” and fisheye lenses “distorting,” but I don’t think that’s very useful or accurate. Rectilinear lenses aren’t necessarily correct - a wide-angle lens has extreme distortion and stretching towards the edges to make the lines straight. That being said, the fisheye effect is very pronounced and extreme, and does render scenes in a characteristic fashion. Portrait photographs of people taken with fisheyes, for example, have cartoon-like bulging noses and so on.

Fisheye lenses are useful for three basic things. First, it’s a lot easier to make a super wide angle fisheye than it is a super wide angle rectilinear lens, so a fisheye lens is going to be cheaper than its rectilinear equivalent. Second, and this is how fisheyes came about, it’s possible to build a fisheye lens which covers a full 180° field of view, which is very handy for scientific photography, particularly of the sky. And third, bulgy wide angle effects are fun for taking crazy trippy photographs.

There are two basic types of fisheye lenses. Circular or 180° fisheyes cover a full (or nearly full in most cases) 180 degree field of view across the narrower side of the image rectangle. These lenses make photos that look like bulging circular balls on a black background. The other type are sometimes called full frame or semi fisheyes and basically offer a cropped field of vision so you don’t get the black areas at the corner of the picture. As a result they only cover 180 degrees of view on the diagonal.

On 35mm cameras, full frame fisheyes usually have a focal length of 8mm, and semi-fisheyes have a focal length of 15mm or 16mm. In near-circular lenses, Japanese maker Sigma sell an 8mm autofocus fisheye for use with EOS cameras, and Belarus maker Peleng sell an 8mm manual-focus fisheye that can be adapted to EOS cameras. In full frame fisheyes, Canon sell a 15mm autofocus fisheye for EOS, and Russian maker Zenitar sell a 16mm manual-focus fisheye lens which can be adapted. There are also popular screw-on adapters that convert ordinary lenses into fake fisheye lenses. Such adapters are virtually all of extremely low quality, but are definitely fun to play with.

A lot of photographers turn up their noses and dismiss fisheyes altogether as gimmicky remnants of the 1970s. Personally I think fisheye distortion can yield interesting effects if used occasionally, but it’s obviously not something you’re likely to use every day. In nature or underwater photography, where there are few straight lines, fisheyes can be a useful tool as well.

 

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