Understanding Your Digital Camera-5

You have probably heard of the term "fisheye" and wonder why fish are accused of distorted sight. It is so they can see their adversaries coming from behind them... their eyes are convex or arched outside of the eye socket to help them see all around them.

This term is also used on wide lenses with such extreme angularity and view that they are nicknamed fisheye lens. The image of the man in front of his house, below, gives a clear understanding of this strange distortion ability. Does this mean that all wide angle lenses distort the image? No, many are prior to this distortion range, usually 18mm and above. The millimeter (mm) size of the lens, given by the size of it's last element before the film or light sensor, is dependant on the relational size of the film or light sensor.

Lens elements are ground glass in very precise mathematical formations to achieve a certain focal purpose. At right are normal configurations of lens elements. Concave glass focuses its image back to a certain distance from the surface while convex focuses up and away from a central origin.

These two types can be combined to achieve certain focal length properties as seen in convex and concave focal point lens elements.

Let's look at millimeter sizes of wide angle lenses and compare them to what angle of view would be seen on a compass of 360 degrees and by the human vision.

We know that 180 degrees is one half of a 360 degree circle. Peripheral vision allows us to see on either side of us as much 160-175 degrees. Some extreme wide angle lenses make a circular image out of rectangular framed picture because of the glass element arrangements. These lens mm sizes range from 8-12mm (circular image) and are very expensive due to the glass element costs.

From 13-16mm, the image is distorted at the edges but may fill the rectangular frame of the image. Objects on the outer edges of the image are going to have more distortion than the center of the image, again due to the glass element configuration. This lens type is most commonly used for sports photography (fast capture speed) such as skiing, snow boarding, and car racing.

From 17-24mm, the image is still slightly distorted at the edges, but a lot less than the previous sizes. This the most common starting area for wide zoom lenses. It is also the size lens that most people find necessary to use for capturing most of the scene in a room. It makes sense that this would be very popular with real estate photography... every room will look larger than it actually is which can help make a sale.

From 24-35mm, the image starts to look more the way we see so this is commonly employed in most family gathering pictures, corporate identity capture, advertising, sports photography and wedding party imaging. In zoom lens design, almost all point and shoot cameras use this mm size within their focal range capacity.

In most cases, 35mm and above are no longer considered to be wide angle lens formations. Above this focal length, they are often referred to as normal view, most like the human eye focal length.

Refer to the following links for more info:

Lens_(optics)

Lens designs

Wide angle lenses