Sigma is teasing a product announcement for December 1, which has different camera sites assuming rather different sorts of new releases. SonyAlphaRumors indicates it will be simply a wide angle lens for Sony E-mount. Asian rumor sites indicate that it will be the announcement of a new line of lenses for crop sensors. This may be because those sites confused Sigma’s nomenclature, mixing DN (short, mirrorless flange-back distances) for DC (crop sensor designs).
Sigma already has the quite popular DN line of crop sensor lenses that includes a 16mm corker of a prime, along with a 30mm and a 56mm; all of which have f/1.4 maximum apertures. In full frame designs, Sigma released DN lenses in 85mm f/1.4; 14-24mm f/2.8; a cheap 45mm f/2.8 and 100-400mm; and the bonkiest of bonkers lenses, the 35mm f/1.2.
Missing in that full frame range is a wide angle large aperture lens, such as the much-admired Sigma 14mm f/1.8 Art designed for DSLRs. The new DN lenses typically push past limits previously seen in lenses designed for the older EF system, which used to be the reference mount system used by Sigma. The shorter flange-back distance inherent in mirrorless cameras; and new technologies introduced in design materials and manufacturing technologies all conspire to allow for wider maximum apertures and/or more extreme focal lengths without sacrificing image quality.
Sigma doesn’t normally pre-publicize an event around a simple lens launch. Previous instances include the releases of the better-than-Art 28mm f/1.4, 105mm f/1.4 and 40mm f/1.4 lenses, along with the more recent 35mm f/1.2 Art. Not many industry watchers would be shocked if Sigma introduces something unusual, like a 12mm f/1.8 DN full frame Art lens on December 1. Sigma President Kazuto Yamaki is slated to do the presenting himself.
A big question becoming more urgent among professional mirrorless shooters is whether or not Sigma will release its lenses in RF or Z mounts. Currently there is no option to adapt Sigma DN glass to those platforms. In the beginning of the Art days, Sigma used the Canon mount system as the reference design mount, as those EF lenses could be mounted via adapters to almost other systems.
When designing DN lenses for mirrorless, Sigma instead used the Sony E-mount as a reference mount platform because its narrower throat is a limiting factor that could be made common across most full-frame mirrorless mounts.
If Sigma does opt to produce Z or RF lenses, it would certainly be most efficient to just use the E-mount designs, but if Sigma saw advantage in the wide-throated mount options, it could theoretically produce something even more bonkers by exploiting all 54mm of its diameter. An optimist might say that the time it would take to design such a line could explain the delay in producing Z and RF mount lenses. A realist would say that the delay simply an appropriate amount of time prior to enough mirrorless bodies being out in the wild to justify new lenses.