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Is there one word to describe the difference between wide angle lenses that have a circular distortion and wide angle lenses that produce images where perspective lines remain straight?

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What's the term for a wide angle lens with not distortion? "Sales hype". –  Olin Lathrop Feb 13 '13 at 19:57

3 Answers 3

up vote 13 down vote accepted

The two types of lenses you refer to are:

  • Rectilinear - lenses which produce straight horizontals and verticals across the image
  • Fisheye - lenses with circular distortion

Rectilinear lenses produce more 'natural' looking images but tend to stretch features towards the edges of the frame, so some subjects, e.g. faces, look odd. But they work well for interiors and landscapes. Fisheye lenses are generally regarded as special effects lenses but Matt's excellent answer gives some more practical uses.

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The terms are fisheye (circular distortion) and rectilinear (straight edges).

Fisheye lenses are often unfairly branded as "special effect" lenses by some photographers, due to their near ubiquitous use in skateboarding magazines in the 90s, and the ease at which you can create unusual images when trained on nearly any subject.

However fisheyes have sever unique and useful properties for photographers and can produce very natural looking images when used appropriately. Firstly fisheyes can be made wider than rectilinear lenses. Much wider. Rectilinear lenses top out at about 90 degree vertical field of view, fisheyes have been made with about 220 degree vertical field of view. That's more than 180 degrees, i.e. you can see behind you!

This makes them well suited to scientific applications, but also times when you are extremely restricted for space as a photographer, or when you want to capture a really wide field of view but don't have time/space to plonk down a tripod and shoot a panorama.

Another useful property is that fisheye lenses preserve the proportions of objects (but not their precise shape) whereas rectilinear lenses stretch the proportions of objects that appear toward the edges of the frame. A very wide rectilinear lens can give an uncomfortably distorted image because of this. Combined with the fact that any horizontal or vertical line passing through the centre of the lens wont be bent at all by the fisheye this effect can be exploited for nature/landscape photography.

The horizon is often the only straight line in natural scenes, so getting the horizon dead centre in the image with a fisheye can often yield an image that looks like it was shot rectilinear, but without any of the rectilinear squashing in the corners. This works very well for beachscapes in particular.

Lack of straight lines in the subject + horizon in centre = very natural image (probably moreso than if shot with an ultrawide rectilinear lens):

© Andy McInroy

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So I was being unfair! :D –  Nick Miners Feb 13 '13 at 11:29
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You can also "correct" some of the distortion of a fisheye lens (and possibly introduce another kind of dissortion) in post, especially if you use a lens that has a neat projection (like this one: photozone.de/canon-eos/526-samyang8f35eos?start=1 ) –  SztupY Feb 13 '13 at 15:27

There's one more thing to add. A lens that is Rectilinear usually has distortion of some kind but a lens that is free of distortion is called aspherical often abbreviated to ASPH.

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Hi Martin - welcome to the site and thanks for your contribution. Your answer is really an appendix to existing answers rather than a complete answer in its own right and as such would be better as a comment on one of the existing answers. You will need a reputation of at least 50 before you can comment. –  Nick Miners Feb 13 '13 at 17:26
    
Aspheric elements might be one way to reduce distortion in a lens design, but they are mainly used to improve corner sharpness I think - is it true that aspherical lenses are free of distortion? –  MikeW Feb 13 '13 at 18:11
    
It seems impossible to have a wide angle lens that is aspherical. Is it possible? If it is possible, then would it simply give the appearance of being further away than where you actually shoot from? –  trusktr Feb 14 '13 at 7:34
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An aspheric lens element is not distortion-free. The use of aspheric lens elements is intended to correct spherical aberration, which results from the plane of focus having a spherical nature at the sensor plane. Aspheric elements may also be able to correct field curvature. As for distortion, I do not know of an aspheric element that actually corrects for that. –  jrista Feb 18 '13 at 21:08

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