Ultra Wide Angle Photography

There is an easy formula for calculating the angle of view for any lens that produces a rectilinear image. In addition to giving a wider angle of view, the image produced by a wide-angle lens is more susceptible to perspective distortion than that produced by a normal lens, because they tend to be used much closer to the subject.
Characteristics
Longer lenses magnify the subject more, apparently compressing distance and (when focused on the foreground) blurring the background because of their shallower depth of field. Wider lenses tend to magnify distance between objects while allowing greater depth of field.