At the time of writing, there are two main types of camera systems: DSLR (Digital Single-Lens Reflex) and mirrorless. At the time of reading the latter may be a relic of a bygone era, so let's have a look at what happened...

Firstly, let's have a whistlestop history of the Single-Lens Reflex (SLR) system.

Single-Lens Reflex (SLR) system

Prior to the development of SLR, all cameras with viewfinders had two optical light paths: one path through the lens to the film, and another path positioned above (TLR or twin-lens reflex) or to the side (rangefinder). Because the viewfinder and the film lens cannot share the same optical path, the viewing lens is aimed to intersect with the film lens at a fixed point somewhere in front of the camera. This is not problematic for pictures taken at a middle or longer distance, but parallax causes framing errors in close-up shots. Moreover, focusing the lens of a fast reflex camera when it is opened to wider apertures (such as in low light or while using low-speed film) is not easy.

The photographic single-lens reflex camera (SLR) was invented in 1861 by Thomas Sutton, a photography author and camera inventor who ran a photography related company together with Louis Désiré Blanquart-Evrard on Jersey. Only a few of his SLRs were made.[1] The first production SLR with a brand name was Calvin Rae Smith's Monocular Duplex (USA, 1884). Other early SLR cameras were constructed, for example, by Louis van Neck (Belgium, 1889), Thomas Rudolphus Dallmeyer (England, 1894) and Max Steckelmann (Germany, 1896), and Graflex of the United States and Konishi in Japan produced SLR cameras as early as 1898 and 1907 respectively. These first SLRs were large format cameras.[2] [3]

The first 35mm prototype SLR was the "Filmanka" developed in 1931 by A. Min in the Soviet Union.[4] In 1933 A.O. Gelgar developed the "GelVeta" also in the USSR, later re-named Спорт ("Sport").[5]

The first 35mm format SLR in large scale production was the Ihagee Kine Exakta, produced in 1936 in Germany, which was fundamentally a scaled-down Vest-Pocket Exakta. This camera used a waist-level finder.

Most SLR cameras permit upright and laterally correct viewing through use of a roof pentaprism situated in the optical path between the reflex mirror and viewfinder. Light, which comes both horizontally and vertically inverted after passing through the lens, is reflected upwards by the reflex mirror, into the pentaprism where it is reflected several times to correct the inversions caused by the lens, and align the image with the viewfinder. When the shutter is released, the mirror moves out of the light path, and the light shines directly onto the film. The viewfinder of an SLR presents an image that will not differ substantially from what is captured by the film as it presents it as a direct optical view through the main camera lens, rather than showing an image through a separate secondary lens.

So, we've now raced through camera development to the point where we have the 35mm film SLR, further refinements of which brought us Through the Lens (TTL) metering and Automatic Exposure. The first autofocus 35 mm SLR was the Pentax ME-F released in 1981.[6]

Up to this point photographic images were captured on film - perhaps the subject for a future article - but advances in semiconductor technology were about to bring about a seismic shift.

Delta-Doped Charged Coupled Devices (CCD) for Ultra-Violet and Visible Detection

A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors that can convert photons incident upon them to electron charges. the first time this technology was used in an imaging context was by Gil Amelio, Michael Francis Tompsett and George Smith in April 1970[7]. Fairchild Semiconductors team, led by ex-Bell researcher Gil Amelio, was the first with commercial devices, and by 1974 had a linear 500-element device and a 2D 100 × 100 pixel device. Steven Sasson, an electrical engineer working for Kodak, invented the first digital still camera using a Fairchild 100 × 100 CCD in 1975.[8]

The large quality advantage CCDs enjoyed early on has narrowed over time particularly since the development of the CMOS (Complimentary Metal Oxide Silicon) sensor by Eric Fossum's team at the NASA Jet Propulsion Laboratory in 1993.[9] Since the late 2010s CMOS sensors are the dominant technology, having largely if not completely replaced CCD image sensors.

The first filmless SLR (single lens reflex) camera was publicly demonstrated by Sony in August 1981. The Sony “Mavica” (magnetic still video camera) used a color striped 2/3” format CCD sensor with 280K pixels, along with analogue video signal processing and recording.[10] The Mavica electronic still camera recorded FM modulated analog video signals on a newly developed 2” magnetic floppy disk, dubbed the “Mavipak”. The disk format was later standardized as the “Still Video Floppy”, or “SVF”.

Replacing film with a similar-sized digital sensor was possible, but expensive because larger sensor areas imply a greater probability that a defect will render the sensor non-functional. Such "full frame" sensor digital SLRs (DSLRs) however gained early popularity with professional photographers who could both justify their initial high cost, and retain the use of their investment in expensive 35 mm film lenses. By 2008, full-frame models such the Canon EOS 1Ds and 5D, the Nikon D3 and D700, and the Sony Alpha A850 and Alpha A900, designed and priced for professionals, were available.

Finally, we reach the DSLR era, all the advantages of decades of SLR camera development coupled with decades of research into CCD and later CMOS sensors to provide the perfect image making device. But then something new happened.

Mirrorless

In late 2008, a new type of camera emerged, called a mirrorless interchangeable-lens camera. It is technically a DSLR camera that does not require a reflex mirror, a key component of the former. While a typical DSLR has a mirror that reflects light from the lens up to the optical viewfinder, in a mirrorless camera, there is no optical viewfinder. The image sensor is exposed to light at all times, giving the user a digital preview of the image either on the built-in rear LCD screen or an electronic viewfinder (EVF).[11]

Mirrorless cameras are mechanically simpler than DSLR cameras, and are smaller, lighter, and quieter due to the elimination of the moving mirror. While nearly all mirrorless cameras have a mechanical shutter, many also have an electronic shutter, allowing completely silent operation.[12] The first digital rangefinder camera commercially marketed was the Epson R-D1 (released in 2004), followed by the Leica M8. They were some of the first digital lens-interchangeable cameras without a reflex mirror, but they are not mirrorless cameras because they did not use a digital display system for live preview.

The first mirrorless camera commercially marketed was the Panasonic Lumix DMC-G1, released in Japan in October 2008. It was also the first camera of Micro Four Thirds system, developed exclusively for the mirrorless system.

Until the mid-2010s mirrorless cameras were somewhat challenged to provide an electronic viewfinder with the clarity and low-lag responsiveness of the optical viewfinders used on DSLRs, especially under strong sunlight or when photographing the sky at night.[13]

The Fujifilm X-Pro1, announced in January 2012, was the first non-rangefinder mirrorless with a built-in optical viewfinder. Its hybrid viewfinder overlaid electronic information, including shifting frame-lines, to compensate for the parallax effect. Its 2016 successor, the X-Pro2, had an updated version of this viewfinder. Canon was the last of the major manufacturer of DSLRs to announce their own mirrorless camera, announcing the Canon EOS M in 2012 with APS-C sensor.

After having debuted at the bottom of the market and having technologically advanced rapidly due to advances in mobile phone camera and video camera manufacturing, mirrorless lens systems created significant interest from camera manufacturers as a possible alternative in high-end camera manufacturing. Mirrorless cameras have fewer moving parts than DSLRs, and are more electronic, which is an advantage to electronics manufacturers (such as Panasonic, Sony and Samsung), as they eyed the market share of dedicated camera manufacturers who had significant advantages in precision mechanical engineering.

On-sensor autofocus is free of the adjustment requirements of the indirect focusing system of the DSLR (which relies on a separate autofocus sensor located below the reflex mirror), and as of 2018 mirrorless cameras could shoot with phase-detect autofocus at up to 20 frames per second using up to 693 focus points—a number far exceeding what was available on any DSLR.[14]

Mirrorless v DSLR: Summary

The rise of mirrorless cameras has disrupted the traditional dominance of DSLR cameras in the professional photography industry.

One of the main advantages of mirrorless cameras is their compact size and weight compared to DSLRs. Mirrorless cameras are typically smaller and lighter than DSLRs, making them more portable and easier to carry around, especially beneficial for professional photographers who often have to travel to different locations and carry multiple cameras and lenses.

A significant technical advantage of mirrorless cameras is their advanced autofocus systems. Mirrorless cameras use on-sensor contrast-detection autofocus (AF) systems, which can quickly and accurately focus on the subject even in low light conditions. In contrast, DSLRs use a phase-detection autofocus system, which can struggle in low light conditions and can require the use of external lighting. The autofocus system of mirrorless cameras is also more versatile, as it can track moving subjects across the frame and can be used for both still photography and video recording.

Mirrorless cameras also offer several features that are not available in DSLRs. For example, mirrorless cameras can shoot silently, which is beneficial for photographers who need to capture images without disrupting the environment, such as while photographing alongside a video shoot. Mirrorless cameras also offer in-body image stabilization (IBIS), which stabilizes the camera sensor to compensate for camera shake and allows for smoother hand-held shooting. This eliminates the need for image stabilization (IS) in lenses, which can be expensive and bulky. When used in combination with IS lenses the effect is multiplied, allowing the possibility of hand holding at remarkably slow shutter speeds.

Mirrorless cameras offer faster burst rates and higher frames per second (fps) than DSLRs. useful for capturing fast-moving subjects such as in sports or wildlife.

In recent years, mirrorless cameras have also made significant advancements in image quality, with many models offering high resolution and dynamic range. This is due to improvements in sensor technology and image processing, which has narrowed the gap between mirrorless and DSLR image quality.

Overall, mirrorless cameras have become the preferred choice for many professional photographers due to their compact size, advanced autofocus system, versatility, and high-performance features. While DSLRs still have some advantages, such as longer battery life and a wider selection of lenses, mirrorless cameras have established themselves as a serious competitor in the professional photography market. As technology continues to advance, it is likely that mirrorless cameras will continue to push the boundaries of what is possible in photography.

References

[1] Coe, Brian (1978). Johnston, Turlough (ed.). Cameras. USA: Crown Publishers, Inc. p. 133. ISBN 0-517-53381-2.

[2] Rudolf Kingslake: The Photographic Manufacturing Companies of Rochester, New York, p. 21

[3] Konishi: Sakura Reflex Prano; source The Japanese Historical Camera, p. 5

[4] Proletarskoe Foto, No. 3, 1933

[5] A.O. Gelgar's Sport, Wikipedia entry

[6] Pentax Imaging Company. "History of Innovations 1980–1989". Pentax history of innovations. Archived from the original on 2007-09-28. Retrieved 2006-10-22.

[7] Gilbert Frank Amelio; Michael Francis Tompsett; George E. Smith (April 1970). "Experimental Verification of the Charge Coupled Device Concept". Bell Syst. Tech. J. 49 (4): 593–600. doi:10.1002/j.1538-7305.1970.tb01791.x.

[8] Dobbin, Ben (8 September 2005). "Kodak engineer had revolutionary idea: the first digital camera". Seattle Post-Intelligencer. Archived from the original on 25 January 2012. Retrieved 2011-11-15.

[9] Fossum, Eric R.; Hondongwa, D. B. (2014). "A Review of the Pinned Photodiode for CCD and CMOS Image Sensors". IEEE Journal of the Electron Devices Society. 2 (3): 33–43. doi:10.1109/JEDS.2014.2306412.

[10] Kihara, N.; Nakamura, K.; Saito, E.; Kambara, M. (June 1982). "The Electrical Still Camera a New Concept in Photography". IEEE Transactions on Consumer Electronics. CE-28 (3): 325–331. doi:10.1109/TCE.1982.353928. ISSN 1558-4127.

[11] Gannon Burgnett. "What's a mirrorless camera and what makes it different from a DSLR?". Digital Trends. Retrieved February 16, 2019.

[12] Corporation, Sony. "Help Guide | Silent Shooting". helpguide.sony.net. Retrieved August 11, 2018.

[13] "Sony's new mirrorless camera EVF is 60 percent sharper". Engadget. Retrieved August 11, 2018.

[14] "Close up | Sony a9 focus modes | Fixation". www.fixationuk.com. Retrieved August 11, 2018.