50 Years of Lens Mount Evolution: Part VI of VI

The last 10 years – digital cameras and image stabilized lenses

The massive adoption of digital cameras has not led – so far – to a dramatic change of the design of the lens mount of the cameras. Canon, Nikon, Pentax and Sony (aka Konica Minolta) did not design specific lens mounts for digital cameras, even if they designed specific series of lenses adapted to the smaller size of the digital “APS-C” sensors.

Panasonic GF1 and G1
Panasonic GF1 and G1 - the most radical development in interchangeable lens cameras since the Contax S and the Leica M3 (Photo courtesy of DPReview)

Only camera makers which had been absent from the 35mm Autofocus SLR market and had no installed base to please had the liberty to start from a clean slate. In 2003, Panasonic and Olympus launched the “Four Thirds” format, combining a relative small size sensor with a large all-electric mount. Last year, Panasonic finally presented the Micro Four Thirds G1, a camera with an electronic viewfinder and interchangeable lenses (EVIL), the first digital camera to really depart from the conventional SLR design of the Contax S of the late forties.

Why did the camera manufacturers keep the same bayonet mount for digital?

When the first digital SLRs from Nikon and Canon were presented in 2000, large imaging sensors were so difficult to manufacture and therefore so expensive that the camera makers settled for a form factor smaller than the 36x24mm dimensions of 35mm film (23.7mmx15.6mm for Nikon, 22mmx14.9mm for the Canon EOS-D30).

This form factor was dubbed “APS-C“, because it was close to the dimensions of an APS picture, shot with the “Classic” image format (25.1×16.7mm) of the APS cameras. The sensor being smaller than a 35mm negative (the diagonal of 35mm film is 1.5 times larger than the diagonal of an APS-C imager), the camera makers had an opportunity to design a new series of smaller bodies and lenses, but they all decided to stick to their legacy lens mounts and to design digital SLRs at least as large as their film counterparts.

Being the undisputed leaders of the film camera market, Nikon and Canon in particular had no interest in starting a new incompatible product line, at the risk of alienating their large user base; it would have leveled the playing field, and offered an easier entry in the dSLR market to companies like Panasonic or Sony. Nikon and Canon also wanted to limit the cost and the technical risk of going digital by reusing most of the components of their film cameras in their first generations of dSLRs. And they may have anticipated that one day, with the help of Moore’s law, cameras using full size digital sensors would become affordable for their professional and enthusiast customers, making their large F or EF bayonets more relevant than ever.

For a few years, however, dSLRs with APS-C sensors were the only game in town. Canon and Nikon both developed specific lenses for their small sensor bodies. Canon decided to modify the EF mount so that the EF-S lenses designed for the small sensor cameras can not be mounted on full frame SLRs or dSLRs. Nikon did not change the F bayonet – small sensor DX lenses can also be mounted on full frame (or FX) bodies, but being designed for the APS-C sensor size, they do not cover the full format of the FX sensors and the image is automatically cropped.

The Four Thirds and Micro Four Thirds formats

In 2003, Olympus and Panasonic launched the “Four Thirds” format. At that time, Canon had already started producing the first full frame 35mm digital camera (the EOS 1D), and was preparing much more affordable 35mm digital SLRs like the EOS-5D for the enthusiast photographer market. A large sensor was still complex and expensive to manufacture, but getting high quality pictures out of it would prove much easier than with a small sensor, in particular in low light situations.

The Olympus Four Thirds system was based on design decisions completely opposed to Canon or Nikon’s . The sensor size chosen for Four Thirds cameras is very small (its diagonal is only half of the diagonal of a 35mm sensor), but at the same time the lenses and bodies are designed around a large diameter bayonet mount (44mm, the same as Nikon’s F), with a relatively long focal flange distance (38mm). When the system was designed, it was believed that a large diameter lens and a long focal flange distance were required to get optimal results from the imaging sensor, but the Leica M8 and M9 have since proven that it was not the case.

On the positive side, the relatively large dimensions imposed by the Four Thirds mount gave the engineers more freedom to design high quality lenses with very fast apertures, but on the negative side the body & lens combination could not be made significantly smaller than the more conventional APS-C cameras of their competitors. To add insult to injury, the relative small size of the sensor proved a handicap in low light situations (all things being equal, small sensors are more subject to noise than larger ones), and steered most of the enthusiast photographers away from Four Thirds cameras. Four Thirds only got traction on the low end of the market.

Size comparison: Nikon 18-55 DX, Olympus 14-42, Panasonic 14-45 Micro 4/3
Size comparison: Nikon 18-55 DX (APS-C), Olympus 14-42 (Four Thirds), Panasonic 14-45 (Micro Four Thirds) - Image courtesy of DP Review

Failing to make a significant impact on the mid-level dSLR market, and completely barred from the professional market dominated by new full frame cameras with extraordinary low light capabilities, Panasonic and Olympus decided to create a new niche for themselves, and launched Micro Four Thirds cameras. Using the same sensor as the “Four Thirds” dSLRs, the Micro 4/3rd cameras have abandoned the reflex mirror chamber and the pentaprism viewfinder of conventional dSLRs for an electronic viewfinder. They are designed for a much shorter focal flange distance (approx. 20mm instead of 38mm, and the mount diameter is also smaller (32mm approx. instead of 44mm).
As a result, the body+lens combination is much more compact than any other dSLR on the market. It’s still difficult to predict how this new category of cameras will fare in the future, but they finally bring something new to the table.

Image Stabilization

The migration from film to digital is without a doubt the most significant evolution of photographic equipment in the last ten years. Image stabilization gained acceptance during the same time, and is now a feature expected by amateurs using digicam as well as enthusiasts and pros using expensive large aperture teles. The objective of image stabilization systems is to compensate automatically the involuntary movements of the photographers, and to produce sharper pictures even at slower shutter speeds.

Canon, Nikon and Panasonic adopted relatively similar systems, all based on the controlled movement of optical modules installed inside the lenses. Minolta, Pentax and Olympus opted for in-camera systems compensating the movements of the photographer by moving the image sensor itself. Apparently both systems produce good results. In-camera image stabilization systems do not require any change to the lens mount, but in-lens systems need to be managed from the body, and require a few more electric contacts. Most of the current lens mounts are all-electric now, and adding a few contacts is an easy done job.

The state of the art in 2009

Pentax: Progressive introduction of the KAF3 version of the K bayonet mount, with autofocus motor in the lens. The majority of the lenses in the product line still need an autofocus motor in the camera body.

Canon: No change to the EF mount of the EOS cameras. Starting with the Rebel and the 20D cameras, Canon used a specific variant (EF-S) of the mount for lenses dedicated to the APS-C format. Canon dSLRs all work with EF lenses, but only the Rebel and 20D, 30D, 40D and 50D cameras can use the EF-S lenses.

Minolta, Konica Minolta and Sony: Progressive introduction of SSM lenses, with the focusing motor inside the lens. The majority of the lenses in the product line still need an autofocus motor in the camera body.

Nikon: Multiple variants of the F mount were used during the last 15 years:
– AF-D: no mechanical difference with the AF mount, the D lenses transmit the focusing distance value back to the body for 3D Matrix Metering
– AF-I: focusing motor in the lens – used for tele-lenses between 1992 and 1996;
– AF-S lenses: ultra-sonic (“Silent Wave”) autofocus motor built into the lens. Most of Nikon’s zoom lenses are now AF-S, and the conversion of prime lenses has started a few years ago.
– The new PC-E (perspective control electromagnetic) lenses now use an electromagnetic diaphragm command. All the other Nikon lenses still use the mechanical stop down mechanism introduced with the F mount in 1959.

Olympus & Panasonic started promoting the Four Thirds format in 2003. Four Third lenses use an all electric bayonet mount. The Micro Four Thirds are more compact, and use 11 electrical contacts instead of 9 for regular Four Third lenses. Thanks to the very short focal flange distance of Micro Four Third cameras, it is easy to develop adapters for Canon EF, Nikon F, Olympus OM or Leica M or R lenses.

Gull in Essaouira (Morroco)
An exception on this blog: a digital picture (Nikon D80) taken in Essaouira - Morroco

50 Years of Lens Mount Evolution – Part V of VI


Point and shoot cameras started adopting autofocus mechanisms in 1977, following Konica’s introduction of the C35 AF.
Pentax and Nikon were the first to show autofocus SLRs with passive autofocus systems (in 1981 and 1983 respectively), but were not successful. For the occasion, both companies had designed a system where the camera body (or prism) housed the focus sensors and the lenses contained the motor used for focusing. Both cameras were using a “contrast detection” autofocus system. Pentax and Nikon had to develop specific variants of their mount (K-F and F3-AF respectively) for the occasion. In the typical Nikon manner, the two lenses designed for the F3-AF will still be compatible with the F4 body launched a few years later.

Minolta and the hybrid design

Minolta A Mount (on the Angenieux 28-70 zoom)
Minolta A Mount (shown here on the Angenieux 28-70 zoom) – note the electrical contacts, the autofocus drive shaft, and the rod used for stopping down the diaphragm. The combination of electrical and mechanical commands is typical of an hybrid design.

In 1985, Minolta took a different approach. Using a much more efficient “phase detection” autofocus module, the engineers of Minolta developed a brand new camera system from the ground up. Abandoning the MD mount, Minolta designed a large diameter bayonet mount, and launched the new series of “A” lenses. No compatibility with the old Minolta system was offered, but it did not prevent the Minolta 7000 from being a huge success. It redefined the SLR category, and with the exception of the Canon EOS cameras, all autofocus SLRs would be following the same design principle for a long time.

The “A” mount – which is still used today on Sony SLRs, is a mechanical-electrical hybrid. The lenses have no aperture ring and the transmission of the aperture parameters between the lens and the body is electric, but the diaphragm is closed to its designated aperture by a mechanical lever. Minolta placed the autofocus motor in the body, and had to implement a telescopic shaft mechanism to control the focusing group of the lenses.

The competition was quick to react. Nikon (at the end of 1985) and Pentax (1987) adopted the same hybrid design, but decided to make the new models compatible with their legacy: their AF bodies could still accept non-AF lenses, and their new AF lenses could also be used on conventional SLR bodies.

Canon’s revolutionary EOS system

EF-lens-mount (source: wikipedia)
EF-lens-mount (source: wikipedia)

Canon needed more time than Nikon to react to Minolta’s innovations, but took a much more radical approach. The EOS system, launched in 1987, adopted an all-electrical approach, using an electrical command for the diaphragm and placing the focusing motor in the lenses (as opposed to the camera’s body). The EOS cameras and their lenses used the brand new EF mount, which did not offer any compatibility with the older FL or FD mounts. The absence of compatibility was a shocker for the faithful Canon users, but the new EOS system was obviously designed for the future: Canon did not need to make any change to the mount since its inception, and the all-electric exchange of information between the body and the lens was adopted progressively by all of its competitors.

At the beginning, most of the EF lenses used a conventional electrical motor to control focusing, but a few pro-telephoto lenses benefited from an ultrasonic motor (“USM” in Canon’s marketing brochures). Ultrasonic motors have a very low inertia and operate silently: USM lenses focus very rapidly, and allow the photographer to adjust the focus manually, after the autofocus process has taken place, and without the risk of breaking a cog wheel or the autofocus transmission shaft. USM lenses gave Canon a huge competitive advantage, in particular for sports and action photography.

Nikon recognized rapidly that mounting the autofocus motor in the lens was the right thing to do, and started converting its professional telephoto lenses to an almost all-electrical design (AF-I mount in 1992), which evolved into the current AF-S mount when ultrasonic (“Silentwave”) autofocus motors were adopted (1996). Pentax and Sony were slower to place the autofocus motor in the lens, and most of their current lenses still follow the original hybrid design of Minolta.

Some of the other camera makers decided not to convert their product line to autofocus (Leica, Konica), while some tried but could not get market acceptance (Olympus, Contax). In all cases, the failure to adopt autofocus relegated the camera makers to a niche market, and all ended up stopping production of SLRs altogether.

Almost 25 years after the introduction of the Minolta 7000, it’s interesting to compare Canon’s strategy with Nikon’s. Canon’s users had to absorb a huge change in 1987 (they had to throw away their lenses and buy new ones if they wanted to use the new EOS cameras), but the EF mount and the lenses have remained the same for the last twenty years. All-electrical USM lenses gave Canon a huge competitive advantage, and Nikon, with its more conservative and evolutionary approach, needed almost 20 years to catch up on the professional market.

The state of the art in 1987

Minolta A Mount on a 700si body (1993)
Minolta A Mount on a 700si body (1993) – Note the electrical contacts, the stop down aperture command, the autofocus drive shaft.

Pentax: KAF version of the K bayonet mount. Mechanical control of the diaphragm, autofocus motor in the camera body.

Canon: New EOS mount, 100% electric. Totally incompatible with the FL and FD mounts

Minolta: New A mount totally incompatible with the old SR, MC and MD mounts. Mechanical control of the diaphragm, electric transmission of the required aperture value from the body to the lens, autofocus motor in the camera body.

Nikon: AF version of the F mount. Mechanical control of the diaphragm, electric transmission of the required aperture value from the body to the lens, autofocus motor in the camera. Upward and backward compatibility preserved on professional cameras and lenses (and with limitations on the consumer grade cameras and lenses).

Olympus: new line of lenses, with no focusing ring (autofocus had to be overriden using a rocker switch on the camera body). The reception of the market was so disappointing for Olympus that they gave up on autofocus SLRs, and reverted to conventional OM cameras until 2003.

House in Brittany - Minolta Vectis S1 - The Vectis, launched in 1996, adopted Canon's all-electric autofocus design
House in Brittany – Minolta Vectis S1 – The Vectis, launched in 1996, adopted Canon’s all-electric autofocus design