The 24mm World Cup
Group C: Regular f2.8 Prime Lenses
Pentax K - Canon EF / EOS Mount Adaptor: Modification
There are some great Pentax K Mount lenses: the new Limited Edition silver lenses are among the finest of their kind; the FA optics are still sought after, particularly the faster versions; and the SMC-A's have a reputation similar to Nikon's AIS range: masterpieces of manual focus lens design.
There remains some kind of problem using the manual focus 24mm on any Canon body, but in principle, a straightforward adaptor (or even adapter) is all that's required to mount the lens on any EF-S mount Canon body. The K-Mount Sigma 24mm and Pentax SMC A* 85mm f1.4 work just fine this way. However, moving up to full frame presents a small obstacle. It looks like this:
With the adaptor mounted on the lens, it's plain to see that the lens elements are well clear of the mirror box, but that the protruding stop-down lever, and its plastic trapezoidal guard fin, are going to cause a problem on a full frame sensor body like the 5D or 1Ds Series . . .
Just the sort of thing the Lord gave us Dremels for. In fact, as you'll notice from the pictures, the adaptor (adapter) as purchased has a kind of Dremelled, agricultural look about it, so you won't exactly feel like you're crayoning a moustache on the Mona Lisa as you do this.
If you intend to use the lens on a Pentax body again, you would be well advised to shave off no more than is absolutely necessary to mount the lens (about 1.5mm). Not having access to a Pentax digital body at this time (will update later) I can't guarantee that the metal lever will be long enough to work as it was originally intended after the modification. However, given the trouble one has finding an older Sigma 24mm that will function on an EOS body, I felt confident in hacking my £30 lens to the max.
First, rack the lens out to minimum focus and place a soft baffle in the barrel to protect the rear element. Then hack away, as roughly or carefully as your engineering pride will permit. Finishing the mod more smoothly would only created more – and finer – shavings, so I've left mine au naturel. This K Mount lens is now ready to begin a new life attached to a 1Ds Series or 5D body, and take part in the tournament final heats . . . .