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 [graphic] National Register Bulletin: How to Improve the Quality of Photographs for National Register Nominations

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U.S. Department of the Interior, National Park Service


Aperture-See f/stop, below.

Baryta substrate or base-The paper upon which emulsion is coated. Baryta is a fiber base paper that is more stable than plastic coated paper.

Brightframes-These are commonly found in range finder type cameras. These are the outlined (rectangular) box seen through the viewfinder that represent the area of the actual photograph. What appears outside of the frame will not be recorded on film.

Contact Print-A contact print is made by "contacting" the negative to a sheet of paper and exposing it. The result is a direct print that is the same size as the negative.

Film-the medium used to capture an image.

Film Speed (ISO)-An arbitrary number placed on film that tells how much light is needed to expose the film to the correct density. Generally, the lower the ISO number, the finer grained and slower a film. ISO means International Standards Organization. This term replaces the old ASA speed indicator. The slower the film, the more light is needed to expose it.

Black and White

ISO 25-100-Very fine grained and low contrast.

ISO 100-400-Fine to Medium grain and higher contrast.

ISO 400-3200-Heavy grain and considerable contrast.

Color Negative Films

The same rule applies to negative color films as black and white films. The lower the ISO number, the finer the grain.

Transparency Films

These are color reversal films. Again, in general, the lower the ISO the finer the grain, and the lower the contrast. Recently, new film emulsions in the ISO 50 to ISO 100 range have been released. They are very fine grained, but are also extremely color saturated. This means the colors are bright and vivid, but not necessarily accurate.

Fixer (Hypo)-A chemical, sodium thiosulfate, used to remove residual silver halides (grain) from films and prints when processing them. Fixer "fixes" the remaining silver halides in place on either film or prints. Fixer is also called hypo.

F/stop-A metal plate or diaphragm that controls the amount of light entering a lens barrel. In most cases, the diaphragm is iris shaped. The larger the hole in the diaphragm, the smaller the f/stop number. For instance, f/1.4 is wide open, whereas f/16 is the smallest hole, or fully stopped down. The reasons to use f/stops are: (1) to get a sharper picture (the smaller the f/stop the sharper the image); (2) to get greater depth of field (the smaller the aperture, the greater the depth of field); and (3) to control the exposure (the smaller the aperture, the less light gets in.

Gelatin-base films-All films are gelatin based. Gelatin is used to bind the emulsion to the plastic film base. This technology has been available for more than a century.

Large format-Generally any film format in which negatives are larger than 4 x 5 inches is considered large format. Other sizes include 5 x 7 inches, 8 x 10 inches, and 11 x 14 inches. Most large format cameras are view cameras, field cameras, or specialty cameras.

Medium format-Any camera that uses 120 size roll film is considered to be medium format. This film is 6-cm wide and yields images that can be from 6 cm x 6 cm to 6 cm x 9 cm. The format is between 35 mm and 4 x 5 inches in size.

Negative film-A reversed (negative) image is created when this type of film is used. Black and white and color negative films are called negative films. The negative image is reserved. Whites are black and blacks are white. When printed, a positive image results with whites being white and blacks being black. And colors are correctly imaged when printed.

Oblique photographs-These photographs are neither perpendicular nor parallel to a given line or surface. Rather than being vertical or horizontal, oblique photographs are shot at an angle (45 degrees, for example).

Parallax problems-This occurs mainly with range finder and twin lens reflex cameras. The distance between the center of the lens and the viewfinder causes parallax. The closer the lens is focused to the subject, the more evident the parallax. The top of the image will be cut off if the range finder or viewfinder is not corrected for parallax.

PC-See Perspective Control Lens

Perspective-control lens - A small- or medium-format manual lens that shifts off its axis in any direction on sliding tracks to correct perspective convergence; shifting is controlled by a screw, a rotating control ring, or by friction.

Positive film-A positive image (such as color slides) is created when this type of film is used. Color transparencies are positive films.

Selenium-A chemical that is used to tone prints for longevity. Selenium leaves the prints with a silver look. Toned prints are less subject to light damage and oxidization.

Shift lens - See Perspective-control lens.

Silver halide-The silver crystals that make up an image on a negative or print. When exposed to light, they create an image. Those that are not exposed are washed off, leaving either a negative (film) or positive (print) image.

SLR - See Single lens reflex.

Single lens reflex-A type of camera that uses a prism and mirror system allowing viewing of the subject through the taking lens of the camera. The photographer looks through the rear of the camera and sees the subject (and focuses) through the lens. When the picture is taken, the mirror swings out of the way and the film is exposed.

Small format-Refers to a small size film such as 35-mm films. The image size is 24 x 36 mm for 35-mm negatives. The sizes of the small format films are: 126, 828, and 110.

Thermal dye prints-A process for generating computer (digital) images on paper using a printer. The process uses thermal dyes to create the color image.

Toning and toners-Changing the visual appearance of a silver image by converting some or all of the silver halides to a different type, resulting in an image tone. This can be accomplished with either prints or negatives. The most common toning colors are brown and sepia.

View camera-A large format camera that has a front and rear standard, bellows between them, and rides on a rail. The photographers views the image from the rear of the camera on a ground glass screen. The camera is capable of swings, tilts, and shifts, which makes it ideal for architectural photography. Due to its size and weight, a view camera is generally used in a studio setting.

Viewfinder screen - In SLR camera, this is the screen upon which a lens projects its image for composition and focusing. The photographer views the viewfinder screen through a pentaprism that makes the image eye-level and so that it appears right-side-up and not reversed. For architectural photography, a viewfinder screen is etched with horizontal and vertical lines resembling the grid of a tic-tac-toe board to aid in alignment and composition.

Vignetting-This refers to the cutting off of image edges (usually the corners) when something interferes with the front of the lens. The most common cause of vignetting is a lens shade that is the wrong size for the focal length being used and using a PC lens at an extreme shift, especially with filters. Wide-angle lenses are often vignetted, because a lens hood was used that was not wide enough.

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