[Dan K] had just such a lens from Sigma, but wanted to get it working fully with a camera using the Canon EF lens fitting. Hacking ensued. The lens in question was a Sigma 15-30mm f/3.5-4.5 EX DG ...

But when [Loudifier] needed an extension tube to do extreme close-ups with a wide-angle lens on a Canon EF-M camera ... outside to help align the camera, adapter, and lens. As the STLs and ...