Saturday, April 06, 2013

M240 vs. M9 Wide Angle Flat Field

One of the things I've curious about the new Leica M is whether there is an improvement in corner vignetting and smearing with wide angle lenses.  I haven't had a chance to check corner resolution (though Roger Cicala's test over at Lens Rentals is good data point) but I did quickly check flat field using the Voigtlander 12mm lens, one which was known for a lot of vignetting on the M9.

Here are the the two flat field images, shot at f/11 with a diffuser against a bright sky, the M9 first and then the M240.
M9 flat field image

M240 flat field image
Just from casual inspection, the M240 would appear to have less vignetting.  I did my best to set the white points to be the same for these images but still the actual color cast should be taken with a grain of salt.

The average amount of light loss on all four corners with the M9 is about 1.54 stops.  The average amount of light loss for the M240 is about 1.44 stops.  Thats just sampling the most extreme pixels and shows a slight improvement.

If we take the center line and plot the light loss we get:

Again, the difference isn't huge but its pretty clear that the M240 is better not only at the very edges but starts to have its slight advantage at about quarter frame from the center.  If you do flat field correction in either Lightroom or Capture One the improved noise floor on the M240 should give it a further advantage, in all making it a better tool for wide angle rangefinder photography.

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