M3 and Summicron 50, production differences

[imxputs@knoware.nl (Erwin Puts/imX)]

A user asked me some questions, the answers to which may be of interest to
other members of this group.
Question one: are there differences between M3 bodies from 1955 and 1961?
Question two: what are the reasons for the quality difference between the
Sumicron 7 element and the later 6 element.
To start with the last question. There is a suggestion by McKeown that
M3-models  with a serial number above 1.000.000 are in some mysterious way
better than their predecessors. I dismantled a 1955 model and a 1962 model
with the help of the chief repairman of Leitz and compared part for part,
including the washers, gears, spindles and whatever. There is no
discernable difference between the two models. By the way, the same
exercise with an M6 revealed very few differences. Most parts from an M3
fit in an M6 and vice versa.
I do not have any explanation why this rumour is so persistent. Maybe it is
just a trick by sellers of Leica equipment to get some more money out of
the deal. There are however some minor construction changes around 1959.
Leica changed the shutterbrakes from a two part to a one part design.
Easier to repair, but ever so slightly more noisier.
My very personal opinion: I would not buy a two stroke M3, not because of
quality problems, but simply ease of use. Any other M3 is a great buy, but
beware of the yellowing' (darkening) of the viewfinder. This is caused by
deterioration of the internal coating. I do not agree with some of this
group that this defect is easily repairable.
Now the lenses.
The old Summicron had 7 lens elements and the newer one(s) have six. Tha
alone explains part of the contrast reduction between the old and the new
one. The lens elements in the old one have a different glass composition
with refractive indices below 1.7 (especiallty the large front element has
a lower RI and therfore is heavily curved). The new one has elements with
RI's around 1,74, creating lenselements that are less curved. This makes
production easier, but also reduces optical defects. The sum of all these
measures is a new optical design. The new Summicron keeps its qualities in
the corners where the old one falls off. Its contrast, definition and
ability to record extremily fine details  at full aperture are way ahead of
the old lens. And yes it still has the famous Summicron plasticity some of
the members of this group rightly stress.
Do not worry about color. The old Summicron was a great performer in this
respect. The new one however, because of its better correction has the
ability do differentiate finer hues. Contrary to popular wisdom, it is more
difficult to design a lens that is perfect for B&W. Corrections for co;or
are easier to design. Therefor if a lens is very good for B&W than it
should be good for color photography too.
Hopes this lengty reaction helps.
Erwin Puts