The optics used in a camera vary depending on the needs of the photographer. Variables such as field of view, f-stop, depth of field, focal length, available light, aperture and exposure time can all factor into the decision.
Do f-stop arithmetic:
Compute subject magnification:
Compute depth of field for a photographic lens:
Compute hyperfocal distance:
Compute field or angle of view:
Compute other parameters:
Compute your exposure value: