RE: Eclair Cameras: RE: RE: Light Meter Issues

[Wade Ramsey <wramsey@bju.edu>]

> All I know is that I set the built in light meter accurately with this=20
comparative method.  I use the Sekonic L-228 Zoom meter to take a=20
reading of a brightly lit surface like a white wall, and then I set the=20
camera's potentiometer to the middle diode after setting the F-Stop....<

Mike Welle,

I just caught up with some of this ACL meter thread, about a month late!  

Let me just comment that since you are reading the white wall with your spot meter and calibrating the ACL to the same white wall, that works fine.  Any tone will work if you are calibrating the ACL to an accurate reflected meter reading of the SAME SURFACE.   The use of a gray card would simply give you the correct exposure for shooting an average type scene in that illumination.  For calibration any surface will work.  White walls give a higher reading and are easier to calibrate to in dimmer light.  

The problem with any TTL meter is that, like any reflected meter, it is simply averaging the overall luminance of the scene.  It doesn't know what part of the scene is important and what is not.  Consequently, if the scene happens to be a subject in front of a white barn the meter will read high and underexpose the flesh tone.  If the flesh tone is in front of a black barn it will tend to overexpose the flesh.  No fault of the meter, it just sees light energy.  You have to aim it at what's important.  In those cases, zooming the lens in to read only a gray card in the position of the subject will give you the correct exposure for the flesh tone and the barn in the background will be white or black, respectively, as it should be.  All TTL or other type reflected meters are calibrated for a mid tone, which is about 18 percent reflectance.

The use of an incident meter solves most of these problems, if it is practical to use it.  It reads illumination, not luminance, and gives the correct exposure for any subject that is in that illumination.  It isn't affected by backgrounds, etc.  The down side of this is that you have to use your judgment on unusual subjects.  For example, if the subject is something that is almost white, the incident meter will give an exposure that will probably be too light for your taste--you'd rather underexpose that subject about a stop to see detail in it (a reflected or TTL meter, on the other hand, will probably underexpose it too much.)  If the subject is very dark, say a black cat in a coal bin, you'll probably want to overexpose it so the details show.  The incident meter will make it very dark, the reflected meter may make it too light.  

Of course, these problems can be severe when shooting reversal, not so much with neg.



Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614

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