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 f4.5 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 Min
24-105mm, which it will replace in daily use.

David