It is used to reduce the amount of light entering the camera when aperture or shutter settings must remain constant. Normal Lens A lens that makes the image in a photograph appear in perspective similar to that of the original scene. A normal lens has a shorter focal length and a wider field of view than a telephoto lens, and a longer focal length and narrower field of view than a wide-angle lens. A meter which determines exposure by reading light reflected from the film during picture-taking. Opening up is increasing the size of the lens aperture or decreasing the shutter speed to admit more light to the film.
Optical axis is an imaginary line passing horizontally through the center of a compound lens system.
Over-development is a term indicating that the amount of development recommended by the manufacturer has been exceeded. It can be caused by prolonged development time or an increase in development temperature, and usually results in an increase in density and contrast. Over-exposure is an expression used to indicate that the light sensitive material has been excessively exposed.