A camera line's popularity will always be down to a number of factors, but one of the most crucial is the range and availability of compatible lenses. However capable the cameras may be, if you don't have the right glass to go alongside them you'll have a hard time convincing anyone to seriously invest in your system.
In this respect, Sony's full-frame E-mount line is perhaps in a better position than most. Alongside a steady stream of the company's own optics, it's had a hand from a number of third parties such as Samyang, Zeiss and Voigtländer. Many of their contributions, however, have been somewhat atypical, either designed specifically for video, or manual-focus only, or just prohibitively expensive. And occasionally, all three at once.
As an example, up until now,…