The 24mm World Cup
Group C: Regular f2.8 Prime Lenses

Sigma 24mm f2.8 MF (Pentax K Mount) v Pentax 24mm SMC-A
Performance at f2.8

The distance to the test target here was approximately one metre. Using the same adaptor as the manual focus Sigma, the Pentax SMC-A showed 2.2m on its distance scale.

Sigma 24mm f2.8 SuperWide at f2.8 (centre)	Pentax 24mm f2.8 SMC-A at f2.8 (centre)
1 points	2 points

Actually, there is very little to separate them here. The on-camera flash is all over the place, and is flattering the Pentax SMC-A shot a little more than the Sigma, but we'll give the Pentax the benefit of the doubt because I like its manual focusing better.

Sigma 24mm f2.8 SuperWide at f2.8 (corner)	Pentax 24mm f2.8 SMC-A at f2.8 (corner)
2 points	0 points

Bear in mind that in this instance, a corner isn't the corner: the lowly 350D hacks away nearly 40% of the image circle. The poor showing of the SMC-A is therefore especially inexcusable. What must the actual corners be like? Also remember that the same adaptor is used for both lenses, ruling out the possibility of mounting alignment or registration issues. By comparison, the Sigma 24mm performs strongly, even wide open.