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Fisheye vs Rectilinear Ultra-Wide angle - Difference?

John Koch , Aug 20, 1998; 12:06 a.m.

Okay, I've done the search, but I still haven't found the answer.

What is the difference between a fisheye lens and an ultra-wide rectilinear lens?

I am aware that fisheyes were developed originally to answer scientific needs, such as meterological studies of the sky, and that (from what I can gather) that fisheye lenses typically take in an angle of view of 180 degrees or greater. But I have seen photos taken by wide angles and photos taken with fisheyes (same subject) that appear to my inexperience eyes to be very similar.

What's the difference?

Responses

Yet Another , Aug 20, 1998; 03:11 a.m.

I too am a bit confused on the terms you mentioned. My recollection is that the general definition of a fisheye would be a lens that produces a circular image on the film rather than a rectangular image. This does not seem to hold true however, as Mamiya, for example, lists a 37mm fisheye that produces a rectangular image.

Glen Johnson , Aug 20, 1998; 07:58 a.m.

Fisheye lenses aren't "fully corrected," and, as a consequence, straight lines that don't pass through the optical center of the lens end up being distorted into a curve (barrel style). In the extreme, a fisheye lens can give a full circular view, encompassing the full field in front of the lens. In less extreme examples, like Canon's EOS EF 15mm fisheye, a full circular view is not achieved.

If you compare the frame you get with the 15mm EOS EF fisheye and the frame you get with the 14mm EOS EF L series "more or less fully corrected" wide angle, you can see some significant differences. The apparant differences are dependent on the subject, and how well you maintain the film plane parallel to the subject plane.

You can get what seem to be fisheye like effects out of the EOS EF 17-35 L series zoom, and it is attributed to gross barrel distortion at 17mm - but actually, when you use this lens, you eventually figure out that if you are careful to allign the film plane so that it is really parallel to the subject plane, the barrel distortion can be barely perceptable with many subjects. I know that's not what you asked, but it is probably the reason why so many working pros like the 17-35L, while so many magazine lens test jockies "turn up their eyebrows at the high barrel distortion test results."

Cheers.

Nelson Tan , Aug 20, 1998; 09:33 a.m.

Don,

Fisheye lenses cover a large area like rectilinear wide-angle lenses, but they are not corrected for barrel distortions and such. Some fisheye lenses like the 8mm Nikkor Fisheye show the entire circle, and are very dramatic. Some fisheyes, like the 16mm Nikkor, are full-frame fisheye. This means that they cover the entire 35mm frame, so the final image is rectangular, unlike the 8mm which project the entire image circle within the 35mm frame. But both the 8mm and 16mm will still qualify as fisheye lenses, based on the lens design.

Mark Ci , Aug 20, 1998; 10:03 a.m.

All lenses produce a circular image, it's just that most of them produce a large enough one that the film crops a rectangular one out of the middle of it.

Compare Philip's reviews of the 14mm and 15mm EOS lenses in the Canon section. Note the appearance of straight lines such as horizons, buildings, etc in each. You'll get the idea.

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