Monday, July 22, 2013

The Rectilinear Fisheye Lens

Hazy Morning In A Hot Air Balloon
 The rectilinear fisheye lens produces a very distinctive look with radical barrel distortion increasing towards the edges of the frame. Seeing nearly everything in front of the camera, a fisheye lens is irreplaceable when space is tight you just have to get everything into the shot. With bulging front elements, it is impossible to use normal screw in filters on a fisheye, though some accept rear mounted filters.
Power Tower
Until just a few years ago, full frame or rectilinear fisheye lenses were rare and expensive, made only by the major camera manufacturers. Today almost every lens maker has a fisheye in their product line, including a few fisheye zooms, and prices have dropped. Shorter fisheyes have also become available for use just on APS sensored camera bodies.
Very Close Alligator With 8mm Fisheye Lens
I recently purchased a Rokinon brand 8mm f3.5 fisheye for use on my Canon APS sensored DSLR. With this combination the lens sees about 170 degrees. It is manual focus and manual f-stop only, a small price to pay for the savings over Canon's 8mm fisheye.
Lines in the top of the frame will bulge up.
Focusing a fisheye lens can be difficult. There is so much in the frame that it is hard to tell where the focus point is. Most of the time I simply set the lens in the f8 to f16 range, set an approximate focus using the distance scale on the lens and depend on the gigantic depth-of-field of the short focal length. This lens also seems to be sharpest in that f-stop range.
Lines in the bottom of the frame will bulge down.
It is absolutely mandatory to pay close attention to the edges of the frame when shooting with a fisheye lens. There is such a wide field of view that it is very easy to include feet, fingers, tripod legs and the like in the frame. When shooting hand-held I tend to lean slightly forward and make sure my elbows are tucked into my chest and my fingers are tightly on the camera body.
Large subjects can be captured from quite close with a fisheye lens.
Great care must also be taken to keep contrast within the frame under control. Again, so much is included in the frame that it is difficult not to have both blacks and whites outside the sensor's range when shooting outdoors. When using a tripod, multiple exposures and HDR processing is a possible solution. When shooting handheld it is a matter of careful framing to try as much as possible to exclude blown out highlights or blocked up shadows from the frame.
Certainly not all subjects are suitable for fisheye photography. When you come upon the right subject, however, there is just nothing else like that distinctive fisheye look.

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