Curvature of Field

(See Curvature of Field.)

Flatness of Field

(See Flatness of Field.)

Field of a Lens

VI. (See Lens, Field of.)

Film

(a) A term applied to the sensitive emulsion or coating on plates and papers. (b) Also a term applied to a sensitive emulsion coated on a flexible support. Used in Kodaks, and similar cameras, taking the place of sensitive plates.

Film Cameras

(See Cameras, Film.)

Film Photography

The use of camera employing flexible films instead of glass plates.

Films

To Remove from Plates. (See Acid Hydrofluoric.)

Filter

(a) The process of straining in order to purify a liquid by passing it through a porous substance which retains any impure substances or sediment. An ordinary filter is made by placing filter paper in a funnel. Collodion is usually filtered through tufts of cotton. Gelatin emulsion is forced through chamois skin by pressure. (b) Filtering rays of light. (See Color Filters.)

Filter Paper

(See Paper Filter.)

Filtrate

The liquid which is passed through a filter.

Finder

A miniature camera usually placed on the front of a camera for viewing the object which is to be reproduced.

Direct-Vision Finder

A finder which is placed on the top of a camera, necessitating the latter being held up to the level of the eye, as the finder is looked through in a straight line toward the subject.

Finger Tips

Finger tips are made of India rubber and should be employed when working with acids or silver solutions.

Fire-Proofing Muslin

One of the greatest inconveniences of flashlight photography is the smoke resulting from the igniting of the flash powder. A smoke bag made of muslin stretched smoothly over a wire frame, and sufficiently large to allow of the flash being made without fear of touching the cloth, will be found a great convenience. The muslin should, however, be made fire-proof by soaking for at least a half an hour in the following solution:

Water ..............................................................

90 ozs.

Common Salt....................................................

2 ozs.

Ammonium Phosphate.....................................

5 ozs.

While soaking the muslin the solution should be kept at about 120o Fahr. After soaking hang up to dry. Should the bag become dirty and require washing, it will have to be soaked in the fire-proofing solution again. The flame should not be allowed to reach even the fire-proofed muslin, as there will be danger of its being consumed by smouldering.

Fixed Focus Camera

(See Camera, Fixed Focus.)