Originally posted by normhead hmmmmmm.... I know my DA*60-250 ƒ4 @200 is sharper than the DA* 200 2.8, but maybe I need bigger sample. Something to look into next time I'm injured and can't get out to take pictures. That's a very interesting take on the subject... I'm not sure I've encountered it before. Thanks for posting.
I've always said, until someone can explain to me why I like my 21 ltd images so much... sharpness is guideline not a pre-requisite. It's not the sharpest, it doesn't have the stellar CA control, but for me it's usually the first prime out of the bag. The 35 ƒ2.4 is faster and sharper, but I would never use it in a place where I could use the 21. I'm sure the laws of physics could explain that, but there isn't any person on earth that I know who could show me what's special about the implementation of those laws in the 21 that makes it special. There's certainly no clues in the test charts.
My guess is that lenses that lenses that render the way the eye sees are valued more than lenses that are more technical in nature. I love my Sigma 8-16 for architecture.. for people or scenery my 10-17 often takes much more appealing images.
An initial suspicion about your preference for the 21mm over the sharper 35mm is that the perspective may be more pleasing, tending to bring out a foreground subject and push the background away. As I wrote - and it's not a deep or original insight with me - what matters is whether a lens gives satisfactory results, not whether it is the sharpest optic of that focal length. And there is convenience. Zooms are enormously convenient, and may capture a fleeting moment lost to the process of changing SFL lenses. There are many trade-offs.
Not too surprised that the 60-250mm can at least match the 200mm f2.8. Zooms of the roughly 70-200mm range (pioneered, I believe, by the Vivitar Series 1), commonly f2.8, include some with excellent sharpness, matching or surpassing many SFL lenses within that zoom range. BUT, generally, (not always), the f2.8 zooms of 70~200mm have higher DXO ratings than f4.0 zooms of the same range from the same manufacturer.
I will confess to being at times obsessed by resolution, and making mistakes all ways, purchasing a lens with mediocre rating for convenience and finding it unsatisfactory, purchasing a lens with outstanding rating and finding no better than what I already owned, taking SFL lenses for quality in addition to a zoom and never taking the former out of the backpack. I must have 20 lenses now (afraid to count) some of which sit lonely and neglected for many months, some not used for years (should put them in PF for sale). Maybe some day.