Canon F1 “Old Style”with Canon Booster T Finder and Canon FD 50mm F1.8 lens.

The TTL metering on the Canon F-1 is a remarkable feature. The photocell is neither in the finder prism nor behind the SLR mirror, but on the side of the focusing screen, which directs a fraction of the light to it. In this way the meter works independently of the attached finder, dramatically simplifying the viewfinders as well as the metering system in the camera. The beauty of it is the focusing screen with an embedded mirror. The exposure meter uses the 1.35volt mercury battery, which fortunately may be replaced, using an ordinary hearing aid battery that is so cheap that it doesn’t matter how long they last. The finder prism is neatly slid on, and focusing screen is easily lifted out.

The Booster T Finder its main function is to expand metering of the Canon F-1 to lower light levels. The CdS built-in the camera body is limited in metering ability , and is not sufficient to perform light metering under dark conditions. In order to solve this problem, the booster T finder was developed to replace the standard pentaprism . When light metering is conducted by the booster side, the aperture must be stopped down to maintain the quality of operation , and preserve the characteristics of the CdS. The window for reading the outside meter is used with the zero speed. The eyepiece shutter is provided to prevent light coming through the eyepiece from affecting the meter. When this shutter is opened , the booster T meter will not function.