when is it a Fisheye lens?

[picture dude]

Looking to buy a wide, wide angle lens, but don't want to mortgage the house.

What I see is some say fisheye and others not? I'm using the S2 and have a 28mm but need to shoot wider angles, so what should I look for ?

I see 18mm, 16mm, 14mm People I spoke with today said they're 16mm was a fisheye, but why not the 14mm? I'm confused????

Gary:confused:

[memobug]

Take a peek here

http://www.archiphoto.com/personal%20pages/Fisheyes.html

http://www.zeta.org.au/~andrewa/ajaa31.htm

Regards,

Matt

[Tom V]

Normal lenses show straight lines as straight. This becomes more difficult to do the wider the lens - things near the edges get stretched looking, but the lines remain straight. In fact, it is hard enough to make the lines REALLY straight, but the more expensive lenses get darn close. When a straight line does not show up as intended, it is distorted. Zoom a cheap wide-to-telephoto lens to the widest angle and lines that are supposed to be straight probably are not.

Example: Stand dead center facing a flat wall. Frame the shot so you can see all edges of the wall, at least top and bottom. Hold the camera level, with the film plane vertical. With a good lens, the top and the bottom of the wall will be straight and parallel to the edges of the frame. With a lesser lens, the top and bottom of the wall may be bent in at the middle of the edges of the frame (pincushion distortion), or bent out in the in the middle of the edges of the frame (barrel distortion). If you don't hold the camera parallel and level with the wall, you will see convergent lines (lines going to a common point, often out of the frame), which is called perspective.

If you had a round object in the center and corner of the above shots, the ball in the center would appear round, and the balls in the corner would appear stretched or egg-shaped. People's heads do the same thing. -But the lines are straight! (or should be.) Wide angle lenses that are designed to render straight lines straight are called rectilinear lenses.

A fisheye lens makes no attempt to make straight lines appear straight on the fllm. Only straight lines that cross exactly on the lens axis will appear straight, all other straight subject lines will appear bent or curved. Objects near the edge do not appear stretched. A fisheye sees more like a human eye (which is spherical). A round ball in the frame will appear round, no matter where it is. However, the extreme perspective gives the appearance that the image is distorted, because we are just not used to seeing an image with this type of perspective.

Fisheye lenses come in two major varieties: Full Frame and Circular.

Circular fisheye lenses project their entire image on the film format, resulting in a circular image in the middle of a dark, unexposed, frame of film. You can see the subject all the way around the edge of the circular image.

Full-frame fisheyes enlarge the image to completely cover the film format. It basically is a cropped rectangle (or whatever the film format is), so you have no unexposed areas on the film.

About the widest rectilinear lens today is a 14mm lens. On a film camera they can see about 114°, while a 20mm sees about 92°. On a digital Nikon or Fuji, which have 1.5x factors (the sensor is smaller than a 35mm film frame), they equate to a 21mm and a 30mm. Canon digital cameras have a factor of 1.6x.

Fisheye lenses can be made in various focal lenghts. There are (were) 16mm fisheyes, as well as 14mm, 13mm, 10mm, and 8mm. Nikon's widest, the 8mm could see 220° - behind itself! Having a lens that wide, with that short a focal length required sticking the back of the lens inside the camera quite a way. The mirror had to be locked up to mount and use the lens.

If that makes any sense, the alcohol must be wearing off.:p