I've got that book. I bought it new, sometime in the mid '70's. It's by Bert Keppler, one of the most knowledgeable and celebrated journalists in American photography. He passed away a few years ago and was still writing enormously useful columns in Popular Photography, up to his passing. In fact I bought a Pentax 10-17 fisheye lens, mostly due to one of his columns detailing how great a lens this was/ is.
BTW, I've also got the Pentax ES ll camera, that followed the Pentax ES, shown on the cover. Bought it around the same time as the book.
I would say, in my humble opinion that I qualify as a Pentaxian.
From one Pentaxian to another, welcome Zazu, to the Pentax forum .