The Origins of the SLR & the Pathway to the Pentax 100th Anniversary

A series of articles counting down to Asahi (Pentax) 100th Anniversary

By Merv-O in Columns on Apr 28, 2019

Pentax Forums will be presenting a series of articles on the evolution of the Single Lens Reflex (SLR) Camera from obscurity to its present iteration known as the DSLR and particularly Pentax's present-day flagship, the K-1 Mark II. The series will continue through November, 2019 when we celebrate the 100th Anniversary of the ASAHI Optical Co., the founders of the Pentax Camera.

Origins of the Single Reflex Camera (SLR)

Many of you are familiar with the SLR as one's every day camera, yet many of you are likewise unaware that the origins of the Pentax SLR (and for that matter, all makes) actually has its origins in the 4th Century BC (circa 330 BC) as a means to protect one's eye from damage in viewing a solar eclipse.

Aristotle and his contemporaries described a metal plate punched with small holes through it and then held up to the sun which would then project a corresponding image onto the ground. In essence, the foundation of photography is based upon this simple optical principle.

In the 11th century, a remedial version of a 'camera obscura' (Latin for 'dark chamber') was developed. A room or a box lit only by a single small hole or window that admitted daylight would create a shadow image of the outside world on the opposite wall. Later in the 13th Century, a medieval inventor named Roger Bacon used the 'camera obscura' technique with mirrors to project optical sites and illusions by projecting sun visions on an opposing wall

Camera obscura concept

However, it was not until the Renaissance period that brought more rapid development of the use of mirrors in creating images. Leonardo Da Vinci is credited with using a camera obscura to draw but that claim has been debunked. In fact, Da Vinci built a small camera obscura to test his theories of the human eye and depth perception, but without a lens, Da Vinci's camera obscura was not effective.

Later in 1550, building on the camera obscura concept, Girolamo Cardano, an Italian mathematics professor, introduced the orbem e vitro, a remedial biconvex lens and wrote about it in his scientific encyclopedia of the era. The introduction of a lens that helped reduced distortion and increased clarity was a huge step forward, but there was still no means of reproducing the improved images the orbem lens produced; still advancements made with the creation of a sharper image through lenses, assisted in the rapid development and dissemination of the Camera Obscura itself.

By the 17th Century, camera obscuras were shrunk in size and were transportable. Their portability alone lended them to be used in various disciplines such as painting an architectural drawing causing a major proliferation of the camera obscura boxes across Europe. In 1676, Johann Christoph Sturm, a professor of Mathematics at Altdorf University in Germany introduced the 'reflex mirror'--by mounting the mirror at a 45 degree angle from the camera lens, the mirror projected the image to a screen above. This core concept is the basis of all DSLR's of today. By coupling the camera obscura with a lens and a diaphragm, the forerunner of the aperture was created--by moving the diaphragm back and forth, the 'aperture' could be made progressively smaller to help sharpen the image. Still, it would be an additional 150 years before early photographic reproductions using the camera obscura technique would become viable.

In the early 19th century large camera with bellows were introduced and they stayed relative static technologically speaking until after the Civil War. Matthew Brady's photographic chronicle of the CIvil War was a major tipping point in pushing the camera into the mainstream. The bulky and cumbersome cameras Brady utilized nonetheless produced some of the greatest pictures in human recorded history.From that point on, the commercial viability of cameras was nurtured, with the public increasingly seeking ways in which to memorialize and record their own lives.

In 1861, Thomas Sutton obtained the first patent for the SLR camera in the UK. Though few examples were built off this patent, but Calvin Rae Smith is credited as developing the first production SLR he dubbed the 'Monocular Duplex' in 1884. In 1889 the original 35mm cellulose flexible format was born when none other than Thomas Alva Edison developed it in his New Jersey Laboratory. Edison later sold the rights to Eastman Dry Plate and Film Company and the Kodak legacy was born. 35mm became the standard (still used today). 

In 1933, the Exacta A appeared. Its introduction was met with little public demand as it used a 127 format. In 1936, Imhagee produced the Kine Exacta which shot 35mm film, similar to other cameras that standardized the film format. Unfortunately World War II disrupted the Imhagee Corp.'s operations and after the war, the remnants of the Imhagee Corp. were in Soviet Controlled East Germany and its Dresden plant was re-opened and due to its former Dutch ties. The highlight of this camera was its interchangeable lens design which endures on all major DSLR model to date. Exactas of the period were marked as "Made in Soviet Occupied Germany" for their exports to the West.

By 1936, Kodak launches Kodachrome with an initial ISO rating of 8 in a canister containing 18 exposures. Brownies, Agfas and other cameras flooded the market and the modern camera in size and shape began to evolve. The Leica Rangefinder system was perfected and it was not until 1949 when an East German company in Dresden created the VEB Zeiss Ikon Contax S which is credited as being the first pentaprism eye-level viewing 35mm SLR and the first with the (infamous) M42 screw mount.

In 1952, the Asahi Optical Company decided to distinguish itself from the other popular manufacturers of the time, to wit, Nikon, Canon, Leica and Contax, et al, who were utilizing the rangefinder system and developed its first SLR model, the Asahiflex. Other than the fact that the Asahiflex was the first SLR produced in Japan, it was not particularly special in its scope other than it broke new ground for Japanese production of SLR cameras; the breakthrough came two years later.

The original Asahiflex - Asahi's first SLR

In 1954, Asahi Optical Company pioneered its Asahiflex IIB model that catapulted the SLR into the basic camera technology still in use today. The breakthrough that turned the SLR into the mainstay of the camera world for the next half-century was Asahi's innovation of the instant return mirror. Up until 1954, when the 'II B' was introduced, all prior SLR viewfinders went black when the shutter was released and had to be manually reset. Once Asahi created the instant return mirror, the SLR went from niche market to volume sales. This was truly the first usable SLR and were extremely popular.

The Asahiflex IIb was a breakthrough with its instant-return mirror

In 1957, Asahi Optical purchased the rights to the name "Pentax" originally registered by VEB Zeiss Ikon and itself derived from combining 'pentaprism' and 'contax'. Thereafter, all Asahi Optical Cameras for export were stamped "Asahi Pentax" and the now iconic 'AOC' prism logo (visible above).

Stay tuned for the next installment: "Asahi Pentax Becomes An Innovative Force in the SLR Camera Industry."


  • "Early History of Single Lens Reflex (SLR) Camera", Frank Mechellhoff (updated 2009)                  
  • 'Asahiflex', Wikipedia, (2019)
  • "A Historic Timeline of the Single Lens Reflex (SLR) Camera 1676-2010", Compiled by Khen Lim (2013).
  • "20th Century Photography", Fotomuseum, Michael Kohler, (2003).

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