Random Orbits said:
When were the 24 L II, 35L, 50L and 85L II released? 2008, 1998, 2006 and 2006. When did Canon say it started designing lenses for higher resolution sensors? Starting with the 70-200 f/2.8 IS II, which was released in 2010, after all the primes you mentioned. The L lenses are designed to give the highest performance, which includes sharpness and corner performance. Compare to those primes to the zooms of their time (24-70 f/2.8, 24-105 f/4 and 70-200 f/2.8 IS) and the primes definitely performed better.
I see the 50 f/1.8 and f/1.4 replacements being the smaller than the L. The Gaussian design is more compact but gets soft with larger apertures, which is why I think it makes more sense for the non-Ls. The L is already much heavier, so going to a retrofocal design like the Zeiss or Sigma makes more sense.
I've had the 50L for a few years after trying the 50 f/1.4 (inconsistent focus at f/2.8 and larger), and one learns to deal with its quirks (focus shift near MFD [I avoid shooting near MFD], needing a better AF system like a 5DIII for off center AF, etc.). I use it primarily in lowlight indoor situations or going for a shallow DOF outdoors. Otherwise, the new zooms are much more convenient. I thought about the Sigma, but I'd hate to alter the way I shoot because of its AF inconsistencies. I'll decide after seeing how the 50L II stacks up.
Designing for higher resolution sensors doesn't necessarily mean that previously designed lenses can't meet the demands of new sensors. I think users of the EF 800/5.6L IS, EF 200/2L IS, 135/2L, 100/2.8L macro IS, TS-E 90/4.5, and MP-E 65/2.8 would agree with me, for instance. These are some of the sharpest lenses Canon produces and they all precede the EF 70-200/2.8L IS II design.
Resolving power at high spatial frequencies is the primary component of "sharpness" in the context of sensors with high pixel density. But I suggest that this should not be the metric by which new lens designs should be measured, because high MTF at high lp/mm is only one aspect of a lens' overall performance, one that is generally only apparent in the image center and in the plane of focus. How a lens produces overall contrast, its field curvature, and the prevalence of chromatic aberrations outside of the plane of focus, are in my opinion very important issues pertaining to the design of fast-aperture lenses.
To see what I mean by this, take the EF 85/1.2L II. It's a great lens, and it actually performs fairly well in terms of center sharpness at high spatial frequencies in the plane of focus when shot wide open. Not as well as an EF 300/2.8L IS II by any means, but for f/1.2, it can resolve a remarkable amount of fine detail. But the chromatic aberration in high-contrast conditions is a killer and the performance outside the plane of focus is problematic. There is always room for improvement. The lens doesn't need to be "sharper"--it needs to be more
well-corrected. The two are not quite synonymous.
Regarding the double-Gauss optical design, it's not the question of double-Gauss versus retrofocus that affects sharpness directly. Rather, it is the space considerations of adding corrective elements that drives the design as well as the extent of correction. Another way of thinking about this is that retrofocus designs don't automatically correspond to superior correction. They facilitate the inclusion of more lens elements, which can be used to correct aberrations and/or shorten the effective focal length of the system.
