Various types of Films and Lenses are used in aerial photogrammetry. Here we have discussed a verious type of films and lenses used in aerial photogrammetry. Photographic film is a sheet of plastic (polyester, nitrocellulose or cellulose acetate) coated with an emulsion containing light-sensitive silver halide salts (bonded by gelatin) with variable crystal sizes that determine the sensitivity, contrast and resolution of the film.
Types of film generally used in aerial photography include:
a. Panchromatic. This is the same type of film that is used in the average hand-held small camera. It records the amount of light reflected from objects in tones of gray running from white to black. Most aerial photography is taken with panchromatic film.
b. Infrared. This is a black-and-white film that is sensitive to infrared waves. It can be used to detect artificial camouflage materials and to take photographs at night if there is a source of infrared radiation.
Color. This film is the same as that used in the average hand-held camera. It is limited in its use because of the time required to process it and its need for clear, sunny weather.
d. Camouflage Detection. This film is a special type that records natural vegetation in a reddish color. When artificial camouflage materials are photographed, they appear bluish or purplish. The name of this film indicates its primary use.
Various Lenses used in aerial photogrammetry:
A simple lens consists of a piece of optical glass that has been ground so that it has either two spherical surfaces or one spherical surface and one flat surface.
Its primary function is to gather light rays from object points and bring them to focus at some distance on the opposite side of the lens .
-A lens accomplishes this function through the principle of refraction.
-Lenses are classified by the curvature of the two optical surfaces.
-A lens is biconvex (or double convex, or just convex) if both surfaces are convex.
-If both surfaces have the same radius of curvature, the lens is equiconvex.
-A lens with two concave surfaces is biconcave (or just concave).
-If one of the surfaces is flat, the lens is Plano-convex or Plano-concave depending on the curvature of the other surface.
-A lens with one convex and one concave side is convex-concave or meniscus. It is this type of lens that is most commonly used in corrective lenses.