Originally posted by Big Dave Hello roentarre,
I realize that the size of the sensor or negative has nothing to do with the image IQ produced by any given lens lens, but the crop factor will effect any tendency to distort.
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Actually, the "crop factor" is more likely to improve a lenses performance. Using the example of the 31mm lens, it has an image circle large enough to cover the 35mm film format. As soon as we put it in front of an APS-C sensor, we are using closer to the center of the image circle, which is where any lens performs the best.
All else being equal, a lens with an image circle larger than is needed will outperform a lens with a barely adequate one.
The photozone tests clearly give the performance edge to the 31mm lens over the 40mm lens. That the 31 is also a stop faster is icing on the cake.
In another thread, I mentioned that in large format photography, my goto lens is the Nikkor 210mm f/5.6. This is a lens that will cover the 5x7 format. By using it on 4x5, I am not only in the sweet spot of it's performance, but I also have lots of good image circle to use for swings and tilts.
This is where alexgn has really gone off the rails with his assertion that the 31mm lens is best used on 35mm film.
By putting it on a DSLR, we are using the best part of a very good lenses image circle.
He has misread both the photozone test, which clearly puts the 31mm lens ahead of the 40mm lens, and he has misread the very person who he is citing as the person who he is using as a poster child for not using the 31mm lens on a DSLR.
This is not to say that the 40mm lens is not a very good lens. It is. However, I also have very reliable information that it is a rework of a 25 year old lens (the old M 40mm Pancake). If so, the 31 is a much more recent lens design, and has the advantage of computer design rather than a room full of people with abacus'.
We have a guy on the PDML like this. He comes up with a nonsensical theory, then doesn't bother to read any factual evidence that disputes his theory, including the very evidence he is using to support his theory that not only doesn't support his arguments, but actually disagrees with what he is citing it to say.