The Canon Speedlite 155A is a compact and reliable flash unit designed for Canon’s A-series 35mm SLR cameras, including the AE-1, A-1, and AT-1. Featuring a guide number of 17 (meters at ISO 100), it offers two automatic exposure modes—green (f/5.6) for subjects within 0.5 to 3 meters and red (f/2.8) for distances up to 6 meters—ensuring consistent and accurate lighting. The flash automatically sets the camera’s shutter speed to 1/60 second when charged, streamlining the shooting process. 

Powered by four AA batteries, the Speedlite 155A delivers over 300 flashes per set, making it ideal for extended shooting sessions. Its straightforward design includes a manual mode for creative control and a pilot lamp that doubles as a flash-ready indicator and test button.  With a flash coverage suitable for lenses 35mm and longer, this unit is a dependable choice for photographers seeking a vintage flash to complement their Canon film cameras.