I may have posted some earlier thoughts on Minolta, Leica and Zeiss. Most comments about Minolta glass refer to lenses made pre-mid-1990s, because they changed their philosophy considerably once the Malaysian plant was opened. When Minolta made all their own glass, from the mix to the coating, they did something which no other maker did at the time (mid-1970s to the end of the first generation of AF lenses). They used the lens coatings to balance colour and contrast, so that an entire set of lenses from 7.5mm to 1600mm (originally) would need no CC filters if tested critically on a single roll of film.
This involved allowing some lenses to have less effective multicoating, in order to keep their contrast lower than would have been theoretically possible. Generally, simpler lenses with fewer air to glass surfaces were given single and double coatings on some surfaces and not the total of up to 9 layers which became possible in the 1980s. Zooms were given more efficient coatings to combat their naturally lower contrast. All the coatings were balanced, with the glass types, to give a neutrally matched colour transmission (Minolta's polariser and ND filters were also extremely accurate). We used Minolta colour measurement systems in the mid-1980s, and again in the early 1990s, to check lenses and filters and found the consistency exceptional.
Leica, for whom Minolta made lenses, elements, prisms and focusing screens (nothing to do with the G series which came long after Leica and Minolta ceased to work together) had never attempted to match colour or contrast and you will find radical differences between (for example) a six-element and seven-element Summicron. What they attempted to do was balance microcontrast and overall contrast (boosting MTF figure finer than 60 cycles at the expense of the important 10-30 cycles range). They also taught this concept to Minolta. It tends to produce a 'liquid, three-dimensional' look because overall tones are quite soft, but textures and surfaces are rendered far better.
Zeiss went in a different direction and picked a cutoff point for MTF, using equipment able to measure up to 400 cycles per mm (beyond the resolving power of any film, and theoretically unusable). They would decide that a particular range of lenses should maintain 60 per cent contrast at 80 cycles - or whatever - and then work like hell on the glass, the design, the coatings to achieve this target and never fail. They also tested each individual lens (in Germany) and retained a certificate against its serial number stating the actual figure for that one lens. Then, if returned for repair, they could instantly spot whether elements had become decentered. I do not believe the Kyocera-Zeiss team ever did this! All Hasselblad lenses were tested. Any lens which fell short was sent back for reassembly, or in the worst case, scrapped. The cycles per mm depended on focal length - tele lenses were not expected to reach the same figure as standard or macro lenses. Since retrofocus lenses naturally have extremely high central resolution, their focus with these was maintaining the edge MTF.
In pursuit of this, Zeiss actually ended up with rather variable contrast, usually as high as the design would permit, and used the T* coating thoroughly. They did not get absolutely consistent colour transmission because they used the coating to maximimise certified performance (chart tests) and not to balance colour. But the coating was so effective they often got high microcontrast plus high overall contrast, when Leitz was claiming the two functions were traded against each other.
Since the mid-1990s all you have is the heritage of these policies. Minolta started using outside sources, set up new factories, introduced cheap kit lenses which don't entirely match the range; Leica started trying to copy Zeiss; Hasselblad discarded Zeiss as sole supplier and went to Fuji, whose 9-layer Electron Beam (Super EBC) is probably the best around along with Pentax and Zeiss. Digital has made it all different, forcing designers to multicoat even the rear surfaces and the glued surfaces of lenses, whether or not this changes the contrast and colour. Avoiding digital sensor flare is now the big challenge. Ideas like 'liquid colour' and 'enhanced textural rendering' are no longer relevant (actually such lenses do worse on digital, as Leica owners have found, and would have REALLY found if Leica had dared to use an AA filter).
Canon and Nikon, like Sigma and Tamron, had entirely different targets in mind with lens design (like 'can we make this specification?') and generally their lenses are a real mixture of different qualities. Nikon's six blade iris, like Pentax's five-blader, gave their 1970s lenses that wiry, enhanced sharpness look - precisely what Minolta avoided, if you've ever seen the wonderful circular iris of the 1966 100mm f2 for example, or the extreme of the manual SLR lenses - can't remember how many blades the 135mm f4 had, but it's in the teens.
Consequently Canon owners have no real idea why Minolta owners get so deeply into lens quality (Canon lenses don't have a 'look') while Nikon and Pentax owners often really didn't like the softer, flare-prone Minolta glass. Leica owners of course have always liked Minolta glass, Minolta copied Leica from 1958 onwards and won Leica subcontracting work because they did it so well. Leica in return got the Minolta M-mount rangefinder system, previewed in 1958, shelved for ever. Minolta got Leica input into the design of the SR reflex series.
But in a way it is all irrelevant now as lenses are not made the same way, or to the same targets, today. If you collect vintage Minolta glass - 1970-80s MD/MC, 1985-1990 AF (particularly) you can enjoy the colour and contrast matching which made Minolta unrivalled for audio-visual production (the XE-1 was one of the few camera designed to space exposures perfectly to fit a Wess mount without needing pin registration - if you own one, check it out). It also made Minolta first choice for film-stills shooting and stop-frame animation - no need to test each lens and carefully fit a Wratten CC/LB filter pack and apply an exposure compensation (etc).
One thing I'll bet - when my CZ 16-80 arrives, it will be very different in contrast, microcontrast and colour transmission to my Minolta 24-105mm, which it will replace in daily use.
