File:Canon EOS 6D with Canon EF 24-70mm F4L IS USM lens and Pentax K-5 with Pentax SMC DA* 16-50mm F2.8 ED AL -IF- SDM lens.jpg - Wikimedia Commons
What is “A” on this lens's aperture ring? You need to push a button to lock in into place. Pentax k1000 with smc Pentax-A 50mm f/2.8 : r/AnalogCommunity
Pentax MZ-5 / ZX-5 35mm Film Camera Review - 50mmF2