Rumors: Sigma RF Lenses Coming, Could Unchain from E Mount Limits

Canon Rumors reports a source indicating that Sigma – which has long hinted at a desire to sell RF mount mirrorless-first-design lenses – will have a small number of its designs available in the coming year. No similar word on whether Sigma would bother dipping into the Nikon Z mount market, which is not a good sign for shooters of the once-number-two mount system.

Sigma has been developing best-in-class mirrorless lenses for a few years now, including the 35mm f/1.2 Art pictured above. But they have been making them just for Sony’s E mount and Sigma’s own house mount, the L Mount Alliance L mount system.

Sony opened up their lens communication protocols back when they were an upstart brand and did not have a full lens lineup. This allowed makers like Tamron and Sigma to not only enjoy unfettered autofocus communications, but also the use of lens-mounted camera controls. Canon, on the other hand, has never licensed these sorts of protocols, although third parties have devised fairly good emulations of the original EF mount communications standards, effectively rendering them an open standard.

Public key encryption involves requiring two keys to unlock data. One key is generally available, and the other is generally hidden. This allows firmware in the camera to store all the public keys for the current lens lineup, and each lens holds in its firmware its corresponding private key. When the extra pins are used, the communications can be encrypted, requiring both the public and private keys. A third party lens would find that the Canon firmware did not have the public key to allow this to work.

Canon’s new R mount, however, uses additional pins for lens controls, accelerometer data that helps with stabilization and other future applications. These pins are also public key encryption enabled, which means that any effort to reverse engineer protocols, if not initially fruitless, could be ultimately futile if Canon wished the standards to not be employed by third parties. Canon has not and likely cannot encrypt the original pin communications, because doing so would render all of their legacy lenses inoperable for new cameras.

If, as the rumor suggests, Sigma is to come out with lenses in 2022 in the RF mount, it raises the possibility that these lenses might not be copies of the ones already designed for E mount, which include camera controls on the lens. Instead, this suggests that the new RF mount lenses will be new lens housings, with or without with new lens designs. This raises the prospect of using the full throat of the RF mount, which is significantly wider than E mount throat, currently used as the design standard simply for having a greatest common denominator for producing a lens design across the most mount formats.

To date, Sigma has made the rational decision in its mirrorless lens designs of using the more limited throat of the E mount because it was – by far – the most popular full frame mount system at the time. Its designs favor retrofocal lens arrangements that take advantage of the necking down of the image path to squeeze through the E mount throat. This has not proved to be overly-limiting, but it could also be the case that some great designs haven’t been exploitable yet without a larger mount format.

Example of a retrofocal design by Sigma (patent for an as-yet-unreleased 28-70mm)