Glossary of Terms

Here are some common photography terms that might be useful:

Aperture priority: User sets the aperture or f-stop, and the camera determines the shutter speed.

APS: Advanced Photo System. Another cartridge-based film system. The film has a magnetic coating that enables additional information to be recorded, such as time, date and a short greeting, as well as other data that can be used by the photo processor. However, some photo processors ignore the information. Other features of APS film include the ability to change film mid-roll; the negatives always remain within the cartridge; the film is never outside of the cartridge except during processing and the film processor can provide an index print. APS film cannot be used by 35mm cameras.

Bayonet mount: A method of attaching a lens to a body that makes use of interlocking flanges on the body and lens rather than a threaded tube that is screwed into a threaded base. Most lenses today also contain electrical contacts that are used to focus the lens, set aperture and other purposes.

Depth of field: Draw a line straight out from the lens and mark two points on that line and — for argument sake — everything between the two points is in focus. That is the depth of field. If the two points are close together, that is shallow depth of field. If the two points are far apart, that is a larger amount of depth of field. Depth of field is controlled by the focal length of the lens and the aperture. As a rule, telephoto lenses have a shallow depth of field, while wide-angle lenses have greater depth of field (see illustration).

Focal-plane shutter: Mechanical device that allows light to reach the film. Usually involves the use of two curtains — metal or cloth — that travel from one side to the other or top to bottom with a slit of light that travels across the film. At slower shutter speeds, one curtain will travel all the way to the left before the second curtain begins its journey, meaning that the entire film plane is exposed to light. This type of shutter sits directly in front of the film. For a flash to synchronize properly, the shutter must be fully open. Hence, the slower shutter speeds are required for proper flash synchronization.

Frame lines: The lines that are seen inside the viewfinder represent the approximate area of the image that is recorded on film. Frame lines are necessary in a rangefinder camera, because it is not possible to magnify or shrink the viewfinder view when a telephoto or wide-angle lens is attached.

Hot shoe: Small slotted bracket — usually on the top of the camera — that allows the user to insert an electronic flash. The flash fires when the shutter is fully open. If the bracket does not synchronize with the flash, then it is known as an accessory shoe.

Leaf shutter: The shutter is contained within the lens and not the camera body. The leaf shutter uses metal blades that full overlap when not in use and then quickly open and overlap again to allow light to reach the film.

Parallax: As the subject moves closer to the camera, what is seen in the viewfinder is not a precise image of the same area that is captured on film. Some cameras automatically compensate for this by adjusting the frame lines or providing additional lines in the viewfinder. The amount of parallax error differs between cameras and is dependent on the placement of the viewfinder in relation to the lens. Single-lens reflex cameras do not suffer from this problem (see illustration).

Rangefinder: A focusing method that employs two superimposed images. When the subject is out of focus, the two images will be shifted slightly — one will be to the left or right of the other. When the subject is in focus, the two images will overlap to form a single image (see illustration).

Reciprocity failure: The correct exposure is a combination of shutter speed and aperture, and any change in the shutter speed or aperture requires a corresponding change in the aperture or shutter speed. For example, moving the shutter speed up or down one setting generally requires a one-stop change in the aperture. During very long or short exposures, extra adjustments are necessary — from one to three f/stops.

Rule of thirds: Composition rule that divides the scene into three rows and three columns. The rule states that the picture is much more interesting if the focal point is not in the center of the photo but rather in one of the outlying regions, preferably at one of the intersection points (see illustration).

Screw mount: Lenses screw into the body of a camera using matching threads on the body and the lens. 

Shutter priority: The user sets the shutter speed, and the camera determines the aperture.

SLR (single-lens reflex): Using a pentaprism and mirror, the user views the scene through the camera lens. Focusing is much more accurate, although the view usually blacks out momentarily while the photo is taken because the mirror must swing up and out of the way. The image in the viewfinder often doesn't cover the entire area that is recorded on film.

Split image: A focusing method where the central part of the image is split either horizontally or diagonally. When the image is in focus, the two halves of the image align (see illustration).

TTL meter (through-the-lens meter): The light-sensitive cells "reads" the light that comes through the lens. It provides an accurate way of metering the light on the film plane. Some electronic flash devices use TTL metering to adjust the output of the flash.

Spot: Meter takes its reading from a central portion of the scene — usually a small circular area.

Center-weighted averaging: Meter reads the entire scene but gives greater weighting to the center of the photo, which is where the subject often is located.

Multizone: The camera reads from several parts of the scene and uses a formula that allows the camera to make its best judgment for exposure information. This is marketed under several names.

X-synchronization: A method of synchronizing an electronic flash with the shutter through use of a cable that connects the camera and the flash.