An alternative form of the cat's eye retroreflector uses a normal lens focused onto a curved mirror rather than a transparent sphere, though this type is much more limited in the range of incident angles that it retroreflects.
42.
There were four new Hexanon lenses offered along with the F . The normal lens was a 52 mm f1.4 with a 49 mm filter thread ( a similar lens was offered later with a 55 mm thread ).
43.
Compression, long-lens, or telephoto distortion can be seen in images shot from a distant using a long focus lens or the more common telephoto sub-type ( with an angle of view narrower than a " normal lens " ).
44.
A lens is considered to be a " normal lens ", in terms of its angle of view on a camera, when its focal length is approximately equal to the diagonal dimension of the film format or image sensor format.
45.
However it becomes disadvantageous for wide angle photography as a wide angle lens for 135 film effectively becomes a normal lens for the DX format ( e . g . 28 mm x 1.5 = 42 mm 135 film equiv . ).
46.
Another result of using a wide-angle lens is a greater apparent perspective distortion when the camera is not aligned perpendicularly to the subject : parallel lines converge at the same rate as with a normal lens, but converge more due to the wider total field.
47.
A normal lens or " normal prime " is a lens with a focal length about equal to the diagonal size of the film or sensor format, or that reproduces perspective that generally looks " natural " to a human observer under normal viewing conditions.
48.
Another result of using a wide angle lens is a greater apparent perspective distortion when the camera is not aligned perpendicularly to the subject : parallel lines converge at the same rate as with a normal lens, but converge more due to the wider total field.
49.
A normal lens then, is one that renders a printed ( or otherwise displayed ) photograph of a scene that when held at'normal'viewing distance ( usually arms-length ) in front of the original scene and viewed with one eye, matches the real-world and the rendered perspective.
50.
For example, buildings appear to be falling backwards much more severely when the camera is pointed upward from ground level than they would if photographed with a normal lens at the same distance from the subject, because more of the subject building is visible in the wide-angle shot.
