Terms

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Aperture
The aperture is the opening in the lens that allows light to strike the film.  The larger the aperture, the more light comes through, however at large apertures depth of field and resolution are reduced. Aperture is measured by f-stops; the bigger the f-stop number, the smaller the aperture.
Cropping
Cutting away the outer parts of an image to rearrange the elements that remain.  May be done digitally or in the darkroom.
Depth of Field
The distance from the foremost element of an image that is in sharp focus to the rearmost element also in sharp focus.  Depth of field is increased with smaller apertures (higher f-stops) or  at lower magnifications.
Diaphragm
A part of the lens that reduces the amount of light that reaches the film.  In modern cameras, the diaphragm is held open while looking through the viewfinder and closes only for the instant that the picture is taken.  The amount that the diaphragm is opened or closed is measured by the f-stop.  See also aperture.

 

 
Exposure
The amount of light that reaches the film.  Exposure is determined by aperture and shutter speed.
f-stop
A measurement of the aperture of a lens.  Smaller f-stops (f 2.8) let more light in than larger f-stops (f 16) and allow faster shutter speeds to be used. Larger f-stops give better resolution and depth of field, however.
Film
A physical medium for making images.  Film is coated with photosensitive chemicals that are changed when exposed to light.  Processing makes these changes permanent and visible.  Negative film forms transparent images that have reversed colors; they are used when a final printed image is desired. Positive, or slide films, form normal, transparent images that can be projected.  Films vary in their sensitivity to light; this is measured by ISO numbers.  More sensitive films have higher ISO numbers, but also larger grain, and thus may not have as good resolution as slower films.

Focus 

Frame
The rectangular border around an image; the rectangular "footprint" of the the image; a single image on a roll of film.

Grain The size of the chemicals which record the light on the surface of the film. Larger grain leads to a "fuzzier" picture.

Image

 

 

ISO  Short for "International Standards Organization", the agency that determined standards for film speed.  Used as an abbreviation for film speeds.  Most consumer films have ISO's between 50 and 3200.  Digital cameras often have ISO equivalent settings.  Faster ISO ratings allow for faster shutter speeds and/or smaller apertures.  Faster ISO ratings usually mean more grain in film images and more noise in digital images.  Used to be called ASA.

Negative Film  When developed, the colors are reversed on negative film.  This film is then used to make a positive print.

Perspective

Photograph

Pixels  The individidual units or "dots" of a digital image.

Processing

Resolution
The ability to distinguish between two points.  The closer together the points are, the greater the resolution.

Shutter Speed  The length of time light is allowed to strike the film or imaging chip. 

Slide

Zooming
In a camera: using a lens with varying focal lengths to change perspective.  Zooming in means using a longer focal length to reduce the angle of view and make objects appear larger; zooming out means using a shorter focal length to widen the angle of view and make objects appear smaller (though more of them fit in the image).  On a computer:  Zooming means to increase or decrease the viewed size of the pixels that make up the image.