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A measure of a lenses ability to hold diminishing details of a subject.  In other words, a measure of a lens sharpness.  

MTF (Modulation Transfer Function)

Usually applies to filters.  Effectively reduces the amount of light passing through the lens without altering the colour or hue of the light.

ND (Neutral Density)

A lens that reproduces the perspective of the human eye.  In other words, a lens which makes the image appear similar in perspective to that of the original scene.  In reality, normal lenses are usually slightly longer than the technically correct focal length.  Roughly approximated by 50mm on 135 format or 35mm on APS-C digital cameras.

Normal lens

Distortion where straight lines are bowed in toward the middle to resemble the sides of a pincushion; present in small amounts in some telephoto and telephoto-zoom lenses.  The opposite of barrel distortion.

Pincushion distortion

Blades, a curtain, plate, or some other movable cover in a camera that controls the time during which light reaches the film.


An exposure mode that lets you select the desired shutter speed while the camera sets the aperture for proper exposure.  If you change the shutter speed, or the light level changes, the camera adjusts the aperture automatically.

Shutter priority

Light striking the subject from the side relative to the position of the camera; produces shadows and highlights to create modelling on the subject.

Side lighting

A flash technique for using the flash at a slow shutter speed.  Flash shooting in dim light or at night at a fast shutter speed often results in a flash-illuminated subject against a dark background.  Using a slower shutter speed with the flash brings out the background details in the picture.  Use of a slow shutter speed with rear curtain sync is particularly effective for illustrating the movement of a stream of light.

Slow sync flash