Asahiflex and in 1954, the Asahiflex IIB . In 1957, the Asahi Pentax combined the fixed pentaprism and the right-hand thumb wind lever. Nikon , Canon and Yashica introduced their first SLRs in 1959 (the F , Canonflex , and Pentamatic, respectively). Through-the-lens (TTL) light metering came to the SLR in