The closest Pentax came to a fisheye prior to the 17mm was the Takumar 18mm, which had an angle of view of 148°. In 1967, Pentax introduced the 17mm fish-eye. There are some discrepancies with whether the Asahi fish-eye lenses had an angle-of-view of 160° or 180°. During the period when Asahi Pentax produced the 17mm lens, it seems there were three versions.

• Fish-eye-Takumar 17mm f/4 (1967-1971)
  • This seems to be referred to in the literature as a Super-Takumar.
• Super-Multi-Coated FISH-EYE-TAKUMAR 17mm f/4 (1971-1975)
• SMC PENTAX FISH-EYE 17mm f/4 (1975-1985)

Many people assume every variant is 180°, but the literature such as brochures seems to tell another story. As you can see from the snippets of various catalog’s shown below, the earliest version seems to be 160°, with some transition between the Super-Takumar and Super-Multicoated being either 160° or 180°, with the later SMC versions being all 180°. What’s the real story? I haven’t been able to find out. Short of physically measuring the earlier two versions it’s hard to tell whether the early versions were indeed 160°, or was it a typo?