“K” is for the Agfa Karat. It’s also for Kandor, a silly little camera by Irwin Corporation.
The Agfa Karat was designed for 35mm film in special ‘Karat-cassettes.’ Later models (post-WWII) did take the standard 35mm film cartridge. The lens popped out for use.
Sometimes I think the Kandor candid camera happened when someone notices a bunch of empty metal boxes lying about, and decided to try to make cameras from them.
The other cameras featured in this A to Z Challenge are linked on this page.