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For the price of the 21/1.4 you can buy an M240 (if you can find one) and shoot at the higher ISOs using the 21/3.4, which is definitely a sharper lens across the frame than the 21/1.4. Might also be worth trying the Voigtlander 21/1.8, which past f/4 is difficult to distinguish from the 21/3.4 other than perhaps somewhat lower micro contrast. It has less CA than the Lux but it also has 'normal' field curvature, so it's possible the corners will be somewhat soft wide open at infinity. The 21 Lux also has some strange field curvature-like behavior, but more in the mid zone areas, especially when stopped down between 2.8-4. The other problem will be coma smearing towards the edges. In my 4-way 21mm lens review, I shot a dusk cityscape scene to check point light source characteristics and all of the lenses require until around f/4 to greatly reduce coma. Of course, for the 21/3.4, that's only a half-stop. There are high-rez Jpeg file download links towards the bottom of the page.
I really like the 21 Lux but its images are less technically perfect than the 21 SEM. For anything like landscape (urban or natural) I will invariably go to the SEM, especially if I want to place the subject off center at an aperture at or wider than f/5.6, unless I want shallow depth of field, or it's dark and I'm not using a tripod. For my uses, the Lux really is unique for near distance people photography, such as available light candids during events.