Canon speedlite 155A.
When used with any camera other than the AE-1, the Speedlite 155A provides typical thyristor automation. You have a choice between two apertures you can use. However, when teamed with the AE-1, the Speedlite 155A automatically sets both the f/stop and the shutter speed. But the later Speedlites designed by Canon also offered similar capability (As what we have refer to as 'dedicated' function - control by the three contact points at the foot of the flash unit, each relay or communicate certain info with the SLR body). Thus, you need not have to specifically locate the 155A for your AE-1
Green Position: f/5.6 (ISO 100), 0.5m to 3m for auto working range.
Red Position: f/2.8 (ISO 100), 0.5m to 6m for auto working range.
Manual Position: Guide Number is 17 (m).
Continuous flash photography with the Power Winder A in close range work.
Flash coverage angle: adequate for any lens from a 35mm lens on up.
Power Source: Four size AA alkaline batteries