Back to the subject of the original post...has anyone on this thread compared the 35 IS with the Sigma 35A extensively?
Maybe not extensively but my friend and I compared his 35A to my 35 IS. The IQ wide open is the same for sharpness, but the Sigma is somewhat better since it has less vignetting (if that even bothers you).
In reality the main comparison comes down to preference. Do you like a heavier build and f1.4 or IS, lighter and cheaper.
Totally agree. Between A grade sharp and A+ sharp there's just no significant difference. I gave up my sigma, which had zero AF problems and was extremely sharp, and settled for canon 35is instead mainly because of smaller size.
The Sigma is sharper several stops sooner. In low light, and for less DOF, the Sigma holds the advantage.
Perspective s purely a function of distance. Focal length has nothing to do with perspective. i have a number of refereed publicatons on perspective, and can assure you that focal length is not relevant.
Focal length does change the framing, depth of field, and amount of background blur. That may alter the final image.
No, I am not a pro photographer, but a psychologist with an interest in perspective.
Formal perspective was devised by Brunelleschi in the Renaissance. Ask an artist if you want to know.
If you change the distance, you change perspective. One way to think about perspective is to imagine loooking at a scene from a fixed position and then imagine a vertical plane at a particular distance. Think of everything within sight projecting on the vertical plane. This is what we do with cameras.
This is not a mere "technicality." Perspective is what it is, and one can't invent new definitions. There are socially agreed upon definitions of things like perspective.