LIGHT METERING

LIGHT METERING

The very Basics ... or 18% gray
Metering systems are calibrated to a certain light value in order to gurantee constant exposure settings: 18% gray is commonly accepted because a typical scene seems reflect the same amount of light as this gray value. As a framework for comparison all these colors reflect light like 18% gray:

Usually this assumption works pretty good but if you expose a scene with a majority of bright colors/grays without compensation in spot or center-weighted mode the camera will darken the picture to 18% gray - the result is under-exposed. On the contrary a scene with lots of very dark colors/grays will be lightened up to this gray value - the result is over-exposed. The camera cannot differ between a white wall in shade or a gray wall in sunshine because the amount of incoming ligth is identical. Most cameras are blind in regard to colors - with just one exception (the Nikon F5) they analyse the world based on different light values.

Typical spots with risks for under-exposure:
• Beach
• Snow
• cloudy Sky

Examples with risks for over-exposure:
• Forest
• Lakes
• Dusk or dawn (lots of shadows)

Dependent on the situations you'll have to compensate up to 2 EV to longer or shorter shutter speeds (fixed aperture) or more or less f-stops (fixed shutter speed). Just "shifting the program" doesn't change the amount of light transmitted to the film.

Note: Print films are very tolerant to wrong exposure while slide films require an accurate metering result. 1-2 EV difference compared to the optimal setting doesn't make a difference with prints whereas a slide image is usually quality for the trash bin in such a case.

Typical scenes for Spot or Partial Metering
You should be aware of the followings points:
• Don't meter to the brightest spot of the scene - this would lead to underexposed
results. Try to find a place which has to be exposed right but always think of
the limitation of the metering system.
• Even spot or partial metering cover a substantial area of the picture (up to
9.5%). E.g. the partial metering in the big picture (slot canyon) above points to
a very bright spot but it surely contains some of the shadowed areas - in this
special case it leads to a correct result.
• Normally print films can process a range of around 7 EV=f-stops (slide film: up
to 5 EV) so you should choose spots which are a little bit darker than shown in
the pictures above. If the amount of contrast in a scene exceeds the limitations
of the film your main subject will be outshined or a "skyline"-effect will
occure. You can use the latter as a stylistic element like in the picture to the
lower left (looks better projected than scanned).

Trick:
You can gain 1 EV by pre-exposing the film:
o switch to multi-exposure mode (#2)
o pre-expose with a high-shutter speed and small aperture to a blank paper
(e.g. 1/2000s, f/22)
o expose your picture (non-compensated)

"Black" will probably not as dense as normal but there shouldn't be any further side-effects.

Typical scenes for Center-weighted Metering
Try to find a larger area which has to be exposed right and -again- think of the limitation of the metering system. In critical situations try to compensate manually which can be well controlled in this mode or change to spot metering.

Typical scenes for Matrix or Multi-zone Metering
Multi-zone metering systems are very easy to use. In primitive cases just POINT & SHOOT. Manual compensation isn't very reliable with difficult scenes because you simply don't know exactly how the camera calculates the settings. After some usage you may get a certain feeling for its reactions in certain situations.