Digital Camera Great Angle Lenses

A lens with a focal distance inferior to normal covers a greater angle than that of the eye, and therefore receives the name of great angular (or simply, angular). If we look through the viewfinder of a reflex camera with a great angular and compare the image to the viewfinder with the other eye, we will appreciate a reduction of the size of the images? Now the occupy a smaller angular space than at plain view and therefore the formal covers a greater angle. This produces a feeling of “getting further”, which is nothing but a reduction of a part of our complete visual field without moving from our place. The angle covered is greater with a shorter focal length.

Angular lenses can be divided into two categories:

Medium angular (in universal format, from 40 mm to 28 mm).
Extreme angular (under 28 mm).

Characteristics of a Digital Camera Lens

When looking through a great angular, one has the impression that everything is further away, but at the same time the image includes more visual field than a normal lens. The images taken with an angular are characterized by a ample angle of vision, great depth of field and perspective characterized by the relative proximity of the scene being photographed. Angular lenses are of enormous use when we can to cover a scene of large dimensions that doesn't “fit” in the image with a normal lens and we can get further away. Therefore, it is used to photograph interior, extensive landscapes and when in situations were the distances are short (crowds, parties, etc.). Medium angular is used more in compact cameras with a fixed lens, because, providing an almost normal perspective, they have more depth of field. When referring to movement of the image, the contrary to what happens with telephoto's occurs: a movement of the camera with an angular has less repercussion in the variation of the frame, which is why we can use somewhat longer exposure times.

Digital Camera Lens Design

As we saw, a lens projects on a flat surface a field that is actually spherical. Our complete field of vision is, to give a value, 180 º in all directions. The lens of the eye projects on the interior of the eye, which is a curved surface, a very wide visual field. While the portion of the field we want to cover with a lens is small enough (telephotos, normal lenses and medium angulars), the projection of a curved space on a plane doesn't present too many problems. Nonetheless, for very wide angles, the rays that come from the extremes of the visual field reach the lens and the film with a strong obliquity regarding the axis (the curvature of the retina corrects this problem). Therefore, there can be distortions that primarily affect the extremes of the frame in the way of stretching of the shapes, specially the corresponding to the planes close to the camera. This type of distortion is usual in extreme angulars, whose projection is corrected in the possible ways to give an acceptable image; DON'T confuse extreme angulars with “fish eyes”, were the projection is radically different. Although many people immediately associate angulars with distortion, this may be more or less appreciated according to the focal length, the position of the plane of the film in regard to the scene and the distance that separates us from it. Angular of a very short focal designed for reflex cameras have to face an apparently irresoluble problem: the focal length is less than the distance between the front of the body (were the mount to place the lens is) and the film (between both is the mirror mechanism). Effectively, it is so, but angulars for reflex cameras are designed following the inverted telephoto technique. Instead of an only converging group placed at a distance from the film equal to the focal length (focus on infinity), can combine a diverging frontal element, placed further away from the film, who's sign is inverted by a posterior converging group.