Upload & Sell: Off
I noticed this post by AhamB suggesting that we need some alt lens "sticky" posts to answer common questions. That seems like a good idea to me, but since no one else has posted one yet, here is my attempt at a FAQ outline mainly focused on alt lens usage on DSLRs. Please post your comments/criticisms/suggestions below, and I will attempt to edit/revise this post to incorporate them. Each item in this FAQ could be (and often has been) the topic of a long and complex thread; however, for an introductory FAQ, one needs to balance the merits of brevity...Show more →
Actually that's only part of the reason...The Canon EF mount shares the same short and versatile registration distance as the Sigma SA mount but the EF mount is larger in diameter, allowing a greater range of lenses to be used.
For instance, most Canon EF lenses can be converted to SA mount whilst retaining their AA and AF functions (not their IS function though) but the rear element of the Canon EF 85mm f1.2L is actually larger in diameter than the bore diameter of the SA mount, making it impossible to convert it for use on the SA mount.
However, the older FD-L versions can be converted to SA mount as they have smaller rear elements.
In general though, after the Canon EF mount, the SA mount can take a greater range of lenses than Pentax mount SLR's and DSLR's and even more than the second most popular SLR/DSLR mount out there, the Nikon F mount.