Originally posted by Spodeworld We had a number of back and forths and in the end it did make sense to me, unfortunately. He said to remove the OS it required a redesign and necessitated different parts that would otherwise not be required (he explained, but I forgot, although it may have had something to do with the barrel redesign w/o OS), increasing the complexities of accommodating Pentax and dimnishing economies of scale. He said as a result it was a costly process and not worth it for such a small market. It's not just them adapting the mount. It was much bigger, costlier effort b/c of the OS removal. In a world where 'repeatability' is highly valued, the small market that doesn't benefit from that is problematic for a manufacturer. I'm not sure why it's so difficult to consider that that might really be a real consideration.
Long ago I was told by the head of Sigma Service in NY that it was due to the aperture control lever and Pentax having much smaller market share than Nikon (which also has an aperture control lever). There is a cost to each new lensmount, and Canon and Nikon are easily covered by volume of sales, while making every lens in Sigma SA is not only a point of pride, but also essentially Canon EF electronics on a K-mount (so truly not much to do). The more "niche" a lens is, like the 120-300/2.8 I was pestering him about, the higher the cost to offer it in a new lensmount. This was before Global Vision, though.
He also said that a few lenses were made without OS in other mounts
because the OEM's requested it, not the users. IOW, when I spoke to him Hoya owned Pentax, and they didn't want Sigma to sell lenses in K-mount with OS for some reason - maybe they thought it would make SR look redundant or ineffective? Also, remember Hoya supplies most of Sigma's raw material (optical blanks), and these are Japanese companies, so they do talk to each other and show respect, even if they compete. Why this no-OS nonsense continues today, I've no idea, but I'm pretty sure Sigma is actually *saving money* by not including OS in a lens that they sell at the same price, which could then offset the price of making fewer of that mount.
*Forgot to add, I have two Sigma lenses in K-mount with OS, the 50-500 and the 17-50 (which I note is no longer sold with OS for Pentax). Just turn off SR, otherwise the results are kinda soft.