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

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Subject: Re: LUG[Leica] Incident light measuremeent
From: Eric Welch <ewelch@neteze.com>
Date: Wed, 22 Dec 1999 09:44:06 -0800

sometime around 12/22/99 3:35 AM, Frank Dernie at FrankDernie@compuserve.com
was heard  to write:


> 1) incident measurement measures the light impinged on the subject.
> Knowledge of the actual reflectance is not necessary to get  a correct
> exposure. 

First of all, this is an incorrect assumption.

> one wishes typically if the scene contrast exceeds that of the film in use.

Not in any accurate way without knowing how much light a surface is
relecting. Not if you want an accurate exposure for the
 given sujbect. Incident meters give you a generic good exposure, ignoring
the reflectance of the subject.

> 2) Basic physical laws mean that an incident meter will give a correct
> exposure 

Again, this is pure speculation. How can phsical law prove what you have in
mind for the resulting photograph? It cannot be accounted for.

> in principle not, unless either the experience of the photographer, or the
> accuracy of the matrix metering algoritm intervenes.

Matrix is irrelevant to this topic. But experience is required, yes.

The question of accuracy, for average situations of average lighting, with
an average range of tones, yes, an incident meter will do a good job. But
for difficult light, in difficult sitautions a reflected meter matched with
experience will always out-do an incident meter.

- --

Eric Welch
Carlsbad, CA
http://www.neteze.com/ewelch

Cynicism often masquerades for sophistication in our society, but more often
than not it's merely an indicator of resentment.