Archived posting to the Leica Users Group, 1999/12/22

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Subject: [Leica] Incident light measuremeent
From: Frank Dernie <FrankDernie@compuserve.com>
Date: Wed, 22 Dec 1999 06:35:50 -0500

Bernard wrote
"As a matter of fact, reflected light metering can and will be *much*
more relevant than incident light values. Just think about high key, low
key and anything else in which you have to make a real choice or
otherwise force events. Who cares how much light hits your object. You
need to know the range of light your object(s) are returning to you, so
you can determine what parts you want on the linear part of the
film-curve, and what parts you choose to live without. This goes for any
premeditated shot of anything at all. It's reflected metering that give
you real spot-on information. Incident metering is only nice for very
average subject and for when you're in an unimaginative mood."


I can not argue with more experienced guys but would like to make a few
points.
1) incident measurement measures the light impinged on the subject.
Knowledge of the actual reflectance is not necessary to get  a correct
exposure. It is still possible to manipulate the exposure to emphasise as
one wishes typically if the scene contrast exceeds that of the film in use.
2) Basic physical laws mean that an incident meter will give a correct
exposure (manipulate to emphasise as required etc). A relected meter will
in principle not, unless either the experience of the photographer, or the
accuracy of the matrix metering algoritm intervenes.
3) The best photographers I know well use incident measurement FWIW, this
is not to denigrate those that don't, just a comment on the, probably
atypical, pros I know. Few use autofocus very much either!
4) IMHO because cameras now have meters built in reflected light
measurement is so prevalent that many photographers today either never knew
(younger ones!) or have forgotten incident light techniques.
5) OTOH I do not normally practice what I preach here. I am an amateur who
has been taking photographs for nearly 40 years now, starting with entirely
guessed exposure and I have sufficient experience to use my M6 meter and
manipulate according to prevailing conditions. But if I am being very
serious I always use incident measurement. My photographs have many
shortcomings but poor exposure is not normally one of them!

Hope I make some  sense Frank