Asahi Optical was a japanese firm that made eyeglass lenses, binoculars, and other optical equipment before and during World War II. After that they added cameras to the list. Their camera line is (at least in the US) called Pentax. In the US, Honeywell imported it for many years, so cameras from the 50s, 60s and early 70s are usually branded Honeywell Pentax, whereas later ones are Asahi Pentax or simply Pentax.
This is, I believe, the camera that really put Pentax in the American eye and established it as one of the Big 5 later on (along with Canon, Minolta, Nikon and Olympus). It got its name from the prototype which used spot-metering. By the time they put it in production, however, they had dropped spot metering in favor of averaging. Still, it was quite a camera and a lot of people bought them. It was so successful for them that the carried the Spotmatic name on subsequent models into the early 80s, when they went with the K-series. Their K1000 is basically a bayonet mount Spotmatic.
One of the big reasons people liked Pentax was their excellent optics. Their lens line was called Takumar, named after lens designer Takuma Kajiwara. According to Wikipedia, Takumars go more-or-less in this chronology:
Takumar - base lens, begins in the M37 mount Asahiflex period.
Auto-Takumar - an M42 screw-mount lens with an automatic diaphram (which means it's normally open for composing, and then stops down only when the user needs it for metering).
Super-Takumar - an M42 lens with a manual/auto diaphram switch and lens coating.
Super-Multi-Coated (aka SMC)-Takumar - same as the Super Takumar, but multi-coated for better optical performance, and they were also capable of full-aperture metering (provided the body could use it).
When Pentax dropped screw-mount in favor of their bayonet K-mount, they dropped the Takumar name, but resurrected it later as Takumar (Bayonet); but these lenses are not multi-coated and don't have the prestige of the screw-mount Takumars.
In fact, that's why I bought this camera. He was at a thrift shop for $35. I wanted a 50mm manual screw-mount lens for a special project, and the 50mm SMC Takumar was made to order for it. I figure I bought the lens and got the body for free. Considering the body works great, I made out very well.
One of Modern Photography magazine's Top Cameras
Camera manual: Orphan Cameras.com
Modern Photography magazine camera test: July 1965