Photography Terminology Continued......

Single-Lens-Reflex (SLR) Camera
Light entering the camera through the lens is reflected up by a mirror behind the lens onto a ground glass screen above. This screen is viewed through the viewfinder and a glass pentaprism which turns the image the correct way up. Other camera functions such as light metering and flash control also operate through the camera lens.

Zoom Lens
A lens which can be adjusted to a wide range of focal lengths without a change in focus, thus an alternative for a number of individual lenses of various focal lengths. A difficult type of lens to design and manufacture, but very useful for the photographer who likes to travel light.