If you’ve been using an interchangeable-lens camera for a while, you’ve probably mused, “Wouldn’t it be nice if all cameras and lenses used the same mount, so any lens could be used on any camera?” As you’ve seen in the section “Can I Use This Lens On This Camera?” that’s not the case, for the reasons explained. But why are there so many different lens mounts?
Basically, it’s because each camera manufacturer designs a mount it feels is optimal for its cameras. Lens makers (including the camera manufacturer) then have to make lenses to work with that mount. For example, when Canon went autofocus in 1987, they developed the all-electronic EF mount, which offered a number of advantages but meant that previous Canon SLR lenses couldn’t be used on the EOS cameras. Nikon, conversely, adapted its F mount for autofocus use, so that longtime Nikon users could use their lenses with the new AF cameras (albeit with manual focusing).
In 2003, Olympus introduced the Four Thirds System, with an entirely new lens mount, designed specifically for a new 17.3x13.0mm Four Thirds System digital image sensor, rather than adapting existing 35mm SLR bodies to digital use as other manufacturers had done. Four Thirds is an open system, so any Four Thirds System lens can be used on any Four Thirds System camera, regardless of manufacturer. The new Micro Four Thirds System created an even smaller mount (although it uses the same-size Four Thirds System image sensor), made possible in part by eliminating the SLR’s mirror box. Micro Four Thirds is also an open system, so all Micro Four Thirds lenses can be used on all Micro Four Thirds cameras (but not on regular Four Thirds System cameras because the lenses’ flange back distance is too short and the lens-mount diameter is 6mm smaller). Regular Four Thirds System lenses can be used on Micro Four Thirds bodies, via adapters.
When Sony purchased Konica Minolta’s SLR technology a few years back, they retained the Maxxum lens mount, and all Sony DSLRs can use Maxxum lenses, as well as Sony A-mount lenses. When Sony recently introduced its mirrorless NEX-3 and NEX-5 cameras, which wrap SLR-sized APS-C image sensors in truly tiny bodies, they also introduced an adapter that permits using the Maxxum/Sony SLR lenses on the mirrorless cameras. The adapter retains auto aperture control, and incorporates a tripod mount—important, since most Sony SLR lenses are much heavier than the tiny camera bodies.
There have been attempts at “universal” lens systems. The M42 screw mount (widely known as the “Pentax universal screw mount,” although Zeiss actually introduced it) appeared on a number of 35mm cameras from a number of manufacturers over the years, and there are so many M42-mount lenses out there that adapters are available to attach them to almost any SLR. Tamron’s T-mount enabled the company to produce one version of each lens and attach it to a variety of SLRs via T-mount adapters. But ultimately, the convenience (and optical performance) of integrated lens mounts prevailed, and today Tamron, like Sigma and Tokina, produces each lens it offers in a variety of mounts for popular film and digital SLRs.