Pekka Buttler (Updated 5/2025)
Sigma SA mount specifications and identification
Mount type: Bayonet mount (three prongs, lens release on camera)
Flange focal distance: 44,00 mm
Sensor/film sizes:
• 36mm x 24mm (SA film cameras; 1992–early 2000s)
• 20,7mm x 13,8mm (dSLRs; 2002–2011) (==> 1,75 x crop factor)
• 23,5mm x 15,7mm (dSLRs and mILCs; 2011–2016) (==> 1,53 x crop factor)
• 26,7mm x 17,9mm (mILCs; 2016–2018) (==> 1,35 x crop factor)
Mount communication:
• 7–9 electronic contacts (spring-loaded at camera-end)
• no mechanical communication
Key characteristics of the mount of Sigma SA lenses:
[1] Three-pronged bayonet mount, 3 edges tapered, 3 straight
[2] Locking groove at roughly 03:45.
[3] Bank of electronic contacts, grouped in 5 + 2 (early lenses) or 7+2 (late lenses)
Basic Information on the Sigma SA mount:
Sigma (Sigma Corporation, Kabushiki-gaisha Shiguma) has been a central actor in the Japanese camera & photo scene since its founding in the 1960s. Initially Sigma was clearly focused on being a modest third party manufacturer, and rarely marketed products under their own brand. During the late 1970s and early 1980s that started to change. Moreover, while changes in the photo industry’s structure (especially the advent of autofocus and the increased importance of electronic camera–lens communication) squeezed most third party manufacturers out of the market, this seems to have suited Sigma just fine.
In 1992 Sigma decided to up its game by introducing their own line of film cameras, using their own mount that was clearly modelled after the Canon EF mount. On its introduction, the Sigma SA mount was one of the first lens mounts that relied solely on electronic communication1. In a somewhat unusual move, Sigma decided to offer a dual bayonet system featuring both an inner bayonet (for regular lenses) as well as an outer bayonet, intended for especially heavy lenses. I have found no sign that the outer bayonet was ever used, and with the 2007 introduction of the Sigma SD14 dSLR the outer bayonet was dropped.
Sigma was also early in the digital revolution, with their first digital SLR having been introduced as early as October 2003 (with only a handful of models by the true pioneers having been introduced earlier).
The Sigma SA mount has had considerable staying power and has accommodated Sigma’s strategy through the shift from film to digital, and through a wide spectrum of sensor sizes. It also looks like Sigma might as late as the mid 2010 have had grand designs for their mount, because two further contacts started appearing on Sigma SA mount lenses (that were however never echoed by added contacts in cameras).
In 2018 Sigma decided to abandon the Sigma SA mount and join the L mount alliance. Given that Sigma alone clearly did not really have the market power to keep an entire lens mount alive, this was in many ways an overdue move.
Adapting to Sigma SA Mount bodies
The Sigma SA mount is – in principle – very similar to the Canon EF mount (size, flange focal distance, electronic mount). Hence, if it can be adapted to Canon EF, it could be adapted to the Sigma SA, assuming a suitable adapter exists. It is however that ‘assuming’ part that is the crux, because the relative lack of popularity of the Sigma SA mount has lead to that there are very few adapters available to the Sigma SA mount and those that exist do not exactly benefit from economies of scale.
As a result, the Sigma SA mount cannot be recommended as a basis for adapting legacy lenses.
Adapting Sigma SA mount lenses
With adapting Sigma SA lenses, the real issue is that the lenses are entirely electronic, including the aperture mechanism. Being able to adjust the aperture of a Sigma SA lens therefore necessitates a Smart Adapter that seamlessly handles the communication between the lens’ mount and the camera’s mount.
Currently Sigma offer such smart adapters allowing the use of Sigma SA lenses on both L mount and Sony FE cameras. While constructing further adapters (to Canon RF, Fujifilm X, MFT, Nikon Z …) is by no means beyond the technical capabilities of the more advanced adapter makers, here again the relative lack of popularity of the Sigma SA mount will likely be an impediment.
Footnotes
- The Sigma SA mount is said to even use the same communications protocol as the Canon EF mount (the only earlier all-electronic mount) and that this happened in agreement with Canon. ↩︎