Description
This likely refers to an accessory light meter made by Canon, probably for their FD or earlier systems. Canon produced several types. It could be a ‘Booster’ meter that attached to the viewfinder prism of cameras like the F-1 or FTb to provide enhanced sensitivity or spot metering capabilities (e.g., Booster T Finder). Alternatively, it might be a simple accessory shoe mounted meter, or perhaps a specialized meter like the Canon Macro Auto Meter designed for close-up work. Without more details, it’s hard to pinpoint the exact model.