The Phisheye Foto page

Fisheye Lenses do NOT Distort Perspective!

Yeah, I know, the book says a fisheye is a distorting lens. A 15mm fisheye is described as a distorting lens, while a 15mm wideangle is "corrected". Only trouble is, the book is wrong.

The following assumes you know something about cameras and lenses. It won't take the place of a photography book or course. It's just supposed to correct one mistake nearly all of them make.

All equipment referred to is for 35mm film. If you use a different film format, the focal lengths will change accordingly - assuming you can find fisheye gear at all to suit your system...

The Theory

Do the following experiment, either in your mind or, better, physically.

Take a rectangular object, such as an A4 pad, and hold it vertically about a 60cm in front of your face, with its long axis horizontal. Note its shape. Now, without moving your eyes, move it across (along its long axis) to the limit of your vision. Note its shape. Now move it to the other side. Note its shape.

Your eyes actually have quite a wide perspective. They lose a lot of definition at the edges, but they do see.

Back to the three rectangles. The one in the middle was roughly rectangular. The ones at the sides, however, were not. Their top and bottom edges converged as they got further away from you. That's pretty basic perspective.

Now imagine looking at a single long rectangle, 60 cm in front of your face. What shape is it? It bulges in the centre, and its sides converge into the distance on either side, exactly as it would appear if you photographed it with a fisheye lens.

The fisheye is not a distorted perspective, it is actually the natural perspective for an extreme wide angle. It works the same way your eyes do. This is why fisheye photos work at all. The "corrected" wide angle lens, on the other hand, distorts perspective.

I fell in love with the fisheye years ago, when I couldn't afford an ultra wide angle so I used a wide-angle adaptor designed for a video camera. On a 28mm wide angle lens, this produced a full-circle image that the makers of the adaptor called a "semi fisheye". It wasn't what I had wanted at all, but I was puzzled that the photos worked as well as they did - often better than the unimaginative full circle photos I had seen in photography books. So I began to ask how and why, and discovered a whole new world.

The original fisheye lenses were photometric lenses designed to take photos of the whole sky, and this is still a major application. There are several different patterns of mapping ("distortion") depending on whether angles or areas are preserved by the mapping, and how. None of the three full circle lens combinations I have used indicate what their mapping is, in fact I suspect that "semi fisheye" means that the makers are not altogether sure themselves. But they are all very different in ways that are not explained by focal length and field of view. By contrast, there is only one "correct" mapping for an extreme wide angle, and that is the one that makes the image of a rectangle parallel to the film plane rectangular on the film. This incidentally means you can't have a corrected wide angle with a field of view of 180 degrees or more - the image would be infinitely large. Panoramic lenses and cameras are different again, with optics in some ways similar to fisheye optics and in other ways to wide angle lenses.

I eventually got tired of the vignetting and lack of aperture control of my original adaptor, and bought another secondary lens, an old fisheye adaptor which converts a 50mm lens at full aperture to an excellent if inconvenient full circle fisheye lens with a 180 degree field of view. This adaptor contains its own manual iris, and has circular scales which mechanically calculate the effective focal length and aperture.

Recently I have been using an N/AI-mount Sigma 8mm f/4 lens, which being a primary lens is a lot easier to use, especially when human subjects are involved. I still keep, and occasionally use, the adaptors as well. The main problem with all three is that they make it impossible to read the camera's built-in mechanical light meter. Bear this in mind when deciding which camera to buy if you intend using a full-circle fisheye! The Sigma's advantage over the 8mm Nikkor is that it is smaller and lighter, and only one stop slower. If I'm shooting photos for fun or art, the two lenses I always take are an AI-converted H-series Nikkor 85mm f/1.8, and the 8mm fisheye. (The third is often a 24mm, I admit corrected lenses have their uses!)

I think "real" fisheyes are circular, though full-frame fisheyes of 15 to 16mm are a challenge all their own. The rules of composition for all fisheyes, circular or full frame, are subtly different to those of conventional lenses. I often need to go back to first principles and ask "Where will the eye go?", which is excellent training for other photos as well.

A well-chosen fisheye really livens up a wedding album. Often one is enough. Too many get irritating very quickly, and more so to some people than to others. It's useless to impress the bride if you offend her daddy, in hard economic terms anyway. And expect no enthusiasm from older photographers!