So lately I've been tossing around the various 21mm options... A lot. Here's a rundown.
I chose not to have ties; it's 1-5 stars, period. That said...
It should be noted that in case of IQ (Image Quality) they're ALL really good. There's not a dud in the bunch. At worst, there's some vignetting (mostly corrected in-camera or in post), maybe some minor distortion (also correctable in post). Most are sharper in the center than the edges; only the SEM really sets the standard here for field flatness, followed by the ZM or Color Skopar. "Slower lenses are easier to make better" is what you're seeing. So it's really splitting hairs. You could give the SEM five stars and the rest four if that makes you happy! Saying the Color Skopar is the last of the bunch is like asking which of your fingers is your least favorite.
I didn't list the Zeiss Biogon T* 4.5/21 ZM because of various colorization issues on the M9, using CornerFix, etc. So to me it just wasn't a contender. Though it's an outstanding performer otherwise (in between the 2.8 ZM and the SEM).
I'll be putting together a more in-depth review of the two Voigtländer options in the near future; especially the Ultron, which will be our next big review.
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