Originally posted by Pål Jensen But you don't use the same lens for the same magnification between various formats; you won't get the same picture that way. You use a lens with a different focal lenght. The fact that you want your 50mm to give images with the same magnification as on the 35mm format is really nothing to do with this discussion. Bokeh is all well and good but a 50/1.4 wide open on APS give so shallow DOF that hardly any three dimentional subjects can be rendered in focus. The 77 Limited has so shallow DOF on APS that anything shallower is virtually useless and/or academic.
Anyway, only a tiny fraction of all images rely on very thin DOF and even a tinyer, if any, rely on DOF thinner than what is available with APS. The DOF argument have less merit than generalization about tilt/shift lenses consequences for various system; an issue without relevance for the vast majority of users. One get the impression that APS have endless DOF but difference between APS and FF is one stop which is hardly distingushable without close side by side comparison, and rarely if ever has much artistic relevance.
Hm, I disagree. I have seen quite a few photos which would have been better with a narrower DOF, but obviously that depends on subject matter.
But I also disagree that 1.4 is useless on APS-C. The smaller the size of sensor or film, the larger DOF, so there is no argument against 1.4 on APS-C I'd say. I like my Takumar 1.4/50mm on APS-C a lot wide open.
Just the other day I used a 645 200mm lens on film (645) and was astounded by the isolation it produced—which was very, very useful for people on the street. The equivalent, roughly, of 120mm on FF (roughly because the ratio differs). By the same token, it can make life difficult when shooting landscapes where you might prefer a large DOF.
There can be no argument against shallow DOF per se, it all depends on the subject and context.