philip_pj
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It's intriguing that the Chinese lens makers have not jumped into the deep end of the APO pool, to keep Cosina, Zeiss and Leica company. Viltrox have a pair of APOs coming soon, at 35mm and 55mm but we see almost none before this time in regular focal lengths. As they clearly do not lack the expertise to do so, it seems to be a decision they have made. It might have something to do with leaving a little CA in their images to boost their appeal in other areas, such as image depth inside a softer aesthetic.
'Some theories suggest that certain aberrations, like LoCA (green/purple fringing) around the focus plane, contribute to the "pop" by increasing perceived contrast and sharpness in that plane.'
Jono Slack has mentioned that he feels that CA may indeed add to sharpness in such lenses; and he contrasts that effect with APOs that remove CA and offer greater detail while not appearing as sharp in viewed images. I reserve judgment on this interesting theory, but it may explain why many lenses that are quite run-of-the-mill (in MTF terms) nevertheless make images that look really sharp stopped down. I have seen this myself, very often.
What often happens in fields of fast-moving technology is a kind of monomania in the design studios, where the narrow pursuit of just one factor precludes a thorough examination of the effect of other innovations. Here, we can point to the attempts to banish CA (using ED/APD glass) and - out of left field - multi-coating as known unknowns.
Most have simply bought the lens producers' PR that these are onwards and upwards unadulterated benefits - advantages over what came before. But we can't trust these people. They have made these decisions by themselves and invested vast sums in them. They have an agenda.
But multi-coating may give with one had and take away with the other. You get better micro-contrast ('enough' of this is also needed for 3D) and saturation and reductions in veiling glare, sure enough. But how close are the resulting images to human vision?
'multi-coating on photo lenses can reduce unwanted tonal gradients, specifically those caused by veiling glare (internal reflections) which reduce contrast and flatten image tones. By applying multiple layers of anti-reflective coatings, lens manufacturers minimize internal light scattering, leading to improved micro-contrast and more precise, sharper tonal transitions.'
It seems to be a factor in why images look so 'good', an effect beloved of real estate agents. It may be that the level of coatings development in 'vintage lenses' (say pre-2000) were a big reason why those lenses have such magnificent 3D. We are looking at a multi-factorial issue here, obviously.
I also want to say that one's experience might help explain why some see 3D more easily. I used medium format film (Fuji 645/690, Mamiya 6/7) for a decade before digital got so big it was hard to ignore. I then used Zeiss Contax lenses on Sony DSLRs, followed by the a7 cameras. What did the MF lenses and the Zeiss lenses have in common, something that formed by sense of what images should look like?
They are all slow (f3.5, f4, even slower, (with just the 21/2.8 as my 'fast' lens) and they were all simple designs, often five elements or so, again excepting the 21mm. They all used coatings from the latter part of the last century. All has some form of CA, though it was minor. 3D became embedded in my imagery, in my mind, and in my expectations going forward.
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