[Leica] Colour rendition

[Erwin Puts <imxputs@knoware.nl>]

The topic of colour rendition of lenses (warm, neutral, green, yellow) has
popped up quite frequently. these days. As usual accurate measurements are
available, but the photographic press is relying on subjective
interpretations.
The ISO 6728 "Determination of ISO colour contribution Index (ISO/CCI)"
sets the rules for determining the contribution of lenses to the colour of
the final camera/film image. The ISO standard defines the  spectral
sensitivity of an 'average' colour film (neg and trans) and then determines
the contribution of the lens to see what deviation you get. This is my
favorite approach: standards and measurable deviations from this standard.
No more interpretations of what is warm or neutral.
Of course I would add Leica adhers to this standard. Full results can be
found in a soon to be released report by my very humble person. As an
appetiser; the ISo 6728 stipulates a CCI of 0/5/4 as standard. Forget for a
moment what CCI 0/5/4 means. It is just a normative quantity, but
measurable by instruments and so much more reliable   than any human
observer can be.
The following Leica M lenses have a 0/5/4 measurement and canbe considered
to all intents and purposes as "neutral" in an objective sense. This list
is not exhaustive, just a sample. I need some more stuff for my next
report!!

Elmarit-M 2,8/28 (recent version)
Summicron-M 2.0/50 (recent version)
Apo-Telyt-M 3,4/135.

Much more in the near future.


Erwin