Asahi Optical (later Pentax) had been producing lenses for the Japanese camera industry since 1929. The predecessors to Minolta and Konica were among them. Then in 1952, with no previous experience in camera making, they produced the first Japanese 35mm SLR, the Asahiflex. At first glance the design bears some resemblance to the Leica III and the Praktiflex. The placement of the film advance and rewind knobs, as well as the shutter speed dials, are in the style of the Leica III, including a separate "action" viewfinder next to the rewind knob, while the body in general resembles the Praktiflex, like the folding waist-level finder and the back door with lock. The direct vision finder, covering the field of view of the normal lens is a rare feature found on Sport, some Alpa cameras and the Praktina, complements the waist-level reflex finder. The top of the folded reflex housing is level with the wind and rewind knobs, adding to the neatness of the design. The nameplate of all models is engraved Asahiflex only. The different model designations apparently appear in the camera instruction leaflets. The lensmount is unique, being smaller than both the Praktiflex, Leica and Praktica screwmounts.
Japan's first SLR had a mirror coupled to the shutter button. Press the button and the mirror goes up, release it and the mirror moves down again. This quick-but-not-yet-instant return mirror was a nice feature for 1952, when most SLRs had to be wound on to get the mirror down again. The waist level finder is non-interchangeable. To solve the inconvenience of a mirror-inversed image on the ground glass and to make eye-level use possible, a small optical viewfinder was on top of the camera. The angle of view for this finder was the same as for the 50mm standard lens. The standard lens for this camera was a Takumar 50/3.5 objective with click-stop aperture (see below). Lenses can only be used with pre-set aperture.
This first version of the Asahiflex had only one flash connector, for FP bulbs. The shutter speed markings for this first model are a bit odd: B, 1/20, 1/30, 1/40, 1/60, 1/100, 1/200, 1/500. Of this early model, only about 7500 cameras are said to have been produced, and only for the Japanese market.
The Asahiflex Ia followed the original Asahiflex in 1953. A number of modifications had been made: the shutter speed numbers have been "normalized" to a series of B, 1/25, 1/50, 1/100, 1/200 and 1/500. Whether this was a cosmetic change or an actual adjustment of the shutter speeds remains unclear. McKeown says that the shutter design had been simplified in this model. A second flash connector (X sync) was added above the first one. Production number: about 11,500 made.
The 1954 Asahiflex IIb is often credited for being the first SLR with an instant-return mirror. However a small Hungarian producer, Gamma, produced a batch of 800 cameras in 1947 with this feature. This Duflex had an instant return mirror and an automatic aperture. Few if any of these Hungarian cameras found their way outside of Hungary. (It seems that a Japanese SLR prototype called Orchid was also tried in 1946 with an instant-return mirror.) The Asahiflex IIb was exported to the US (see below) and made in larger numbers. Let's call the Asahiflex IIb the first 35mm SLR with an instant return mirror the rest of the world was aware of.
The Asahiflex IIa has a slow speed dial on the front of the camera, just like on the Canon Hansa and the contemporary Leica IIIf. Slow speeds from 1/25 to 1/2 are now possible and this change justifies the introduction of a camera controlled instant return mirror. Suppose you were able to set the shutter speed to 1/2s and let go of the shutter button on an earlier Asahiflex, the mirror might fold back with the shutter curtains still open.
In 1957, the Asahiflex series was discontinued in favour of the new Asahi Pentax, a rethinking of the way Pentax made SLRs.
As pointed out above, all Asahiflexes are just marked Asahiflex. Some export Asahiflexes were rebadged "Tower" by Sears in the US. For example, the Asahiflex Ia was sold as Tower 23. So was the model IIb with the Takumar 50/3.5. This IIb with a different lens, the Takumar 58/2.4 however was sold as "Tower 24". Apparently the new mirror construction was less of an issue to Sears than the maximum aperture of the standard lens.
The Asahiflexes take 37mm screw mount lenses. A 37mm screwmount is rather unique. The lenses were named Takumar after Takuma Kajiwara, a Japanese painter and uncle of the company director. Apart from the curious screw mount, the Takumars have some other interesting quirks. The aperture is pre-set and made up of 20 (!) blades  giving a nice round lens opening. 50 and 58mm standard lenses were available and 83, 135 and 500mm telephoto lenses. No wide angle lenses were made, apparently because of the presence of the mirror in the light path.
- McKeown 10th ed., p.76.
- http://home.wanadoo.nl/aocn/divers/mag10.pdf, article in Dutch on the development of the Asahiflex by Gerjan van Oosten.
- http://pagesperso-orange.fr/Krg/index.htm under 'historique'.
- McKeown 10th ed., p.212; Camera Magazine no.113, January/February 2008, pp.108–9.
- http://home.wanadoo.nl/aocn/divers/mag11.pdf, nicely elaborated article by Gerjan van Oosten on Takumar lenses, in Dutch.
- Asahiflex and the pre-1959 Asahi Pentax cameras, F. C Sherfy, 1994, ISBN 0-9641107-5-X
- The ultimate Asahi Pentax screw mount guide, Gerjan van Oosten, 1999, ISBN 90-1244-35-x
- The Asahiflex on Wikipedia.
- Asahiflex development and Takumar lenses, articles by Gerjan van Oosten at the Asahi Optical Club Nederland
- Asahiflex model overview
- The Asahiflex in Krg's Pentax collection.
- Pentax Asahiflex on Sylvain Halgand's www.collection-appareils.fr
・Asahiflex Ⅰ in ldnakkun muuseo at https://muuseo.com/f5m6f4e/collection_rooms/9