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.
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?
I love vintage lenses, and in the future, I will be posting much more on them. The question I want to look at here is the usefulness of vintage fish-eye lenses on crop sensors. Typically 35mm fisheye lenses are categorized into circular, and full-frame (or diagonal). A circular fisheye is typically in the range 8-10mm, with full-frame fisheye’s typically 15-17mm. The difference is shown in Figure 1.
Fig. 1: Circular 7.5mm versus full-frame 17mm
The problem arises with the fact that fish-eye lenses are different. So different that the projection itself can be one of a number of differing types, for example equidistant, and equisolid. That aside, using a fisheye lens on a crop-sensor format produces much different results. This of course has to do with the crop factor. An 8mm circular fisheye on a camera with an APS-C sensor will have an AOV (Angle-of-View) equivalent to a 12mm lens. A 15mm full-frame fisheye will similarly have an AOV equivalent of a 22.5mm lens. A camera with a MFT sensor will produce an even smaller image. The effect of crop-sensors on both circular and full-frame fisheye lenses is shown in Figure 2.
Fig.2: Picture areas in circular and full-frame fisheye lenses on full-frame, and crop-sensors
In particular, let’s look at the Asahi Super Takumar 17mm f/4 fish-eye lens. Produced from 1967-1971, in a couple of renditions, this lens has a 160° angle of view, in the diagonal, 130° in the horizontal. This is a popular vintage full-frame fisheye lens.
Fig.3: The Super-Takumar 17mm
The effect of using this lens on a crop-sensor camera is shown in Figure 4. It effectively looses a lot of its fisheye-ness. In the case of an APS-C sensor, the 160° in the diagonal reduces to 100°, which is on the cusp of being an ultra-wide. When associated with a MFT sensor, the AOV reduces again to 75°, now a wide angle lens. Figure 4 also shows the horizontal AOV, which is easier to comprehend.
Fig.4: The Angle-of-View of the Super-Takumar 17mm of various sensors
The bottom line is, that a full-frame camera is the best place to use a vintage fish-eye lens. Using one on a crop-sensor will limit its “fisheye-ness”. Is it then worthwhile to purchase a 17mm Takumar? Sure if you want to play with the lens, experiment with it’s cool built-in filters (good for B&W), or are looking for a wide-angle lens equivalent, any sort of fisheye effect will never be achieved. In many circumstances, if you want a more pronounced fisheye effect on a crop-sensor, it may be better to use a modern fisheye instead.
NB: Some Asahi Pentax catalogs suggest the 17mm has an AOV of 160°, while others suggest 180°.
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