[Leica] exposure rules

[Erwin Puts <imxputs@knoware.nl>]

>Kevin wrote:
>Tonight I was shooting over by my favorite broken down pier.  There's a
>rotted out metal row boat I placed in the foreground, water in the mid to
>background, and rotted piers in the background (nice reflections in the mid
>ground).  So the frame from bottom to top was: boat resting in the mud,
>water (seen through the boat as well), reflections, and pylons.  The boat
>spot metered at about EV 7, the water around 10 (late in the day with heavy
>overcast so the color was steel gray), the pylons and reflections around 7
>or 8.  I was using E100S.
>So the question is,  what would you expose for?
>I decided I wanted very little if any detail in the boat hull so that
>started me off at EV 9.  This also put the water at zone VI or more.
>Conversely, I suppose I could have decided that I wanted the water a little
>hot and put it at zone VI and arrived at pretty much the same exposure.
>So Ted (or anyone else), if you're reading, what do you mean by metering for
>the highlights?  If the hottest reading in the scene is the water at EV 10,
>what exposure value do you shoot?
>PS.  For whatever it's worth, I spot read a gray card at just under EV 9.
>*
>Eric wrote to answer this question:
>It would help to not think in EV at all. With an incident meter, EV would
>be whatever the meter says. You use Zones if you're taking reflective meter
>readings. So say you're shooting a bride with a white dress. You meter the
>bright part of the dress at about Zone VII and leave it. Don't bother
>metering the shadows. Let them go where they may. Slide film demands you
>keep the highlights from blowing out. Lack of detail in the highlights
>kills slides faster than about anything else.

First of all: EV (exposure value) has nothing  to do with incident or
reflective metering. Any exposure meter gives you EV readings at both
methods. EV is nice if you need to do contrast analysis. That works in
incident and reflective modes. If you measure on the bright side an EV of
16 and on the dark side one of 9 you know that you have a seven stops
brightness range. You can measure the bright light and the shadow side with
an incidence meter (from the object to the light source). You can also
measure the light part of the object with a reflective (spot) meter and the
dark part with a spot meter in EV's. Same technique. What  to use when is a
matter of preference and experience.
If you measure a light source with an incident meter you only measure the
luminance level of the light falling ON the object.  (presented to you in
EV's or aperture/speed combinations, which is efectively the same).
The meter being calibrated as it is, assumes that the luminance level
should be translated to a standard luminance level that will peg the 18%
gray reflection values somewhere in the middle of the characteristic curve.
Mostly the meter is right.

Now if you do an analysis of the absolute brightness (reflection) of a
scene and its brightness distribution, you do a series of spotmeterings.
ANY reading from whatever part of the scene is interpreted by the meter as
a 18% reflection value. Metering for the highlights is just this: make a
reading of the brightest part of the scene you wish to have detail and
OVERexpose by 1 or two stops relative to the metered value. Example: you do
a highlight reading at EV 16. The meter, truthfully will interpret this as
a 18% gray card reading and suggests a EV 16 in order to have that part of
the scene rendered as grey. THAT is the crucial idea. You do not want grey
but white: so you overexpose: how much depends on film etc.

Now for the boat scene. If the greycard reading is EV9, then the zone V is
also 9. The boat then (at 7) will be in Zone III (that is darkish). The
water at 10 is zone VI, that is a lighter shade of grey. I do not see ANY
highlights here. They would be in Zone VIII or even IX, that is EV's 11 or
12. In the scene presented there is no highlight measured and so none to
compensate for. If you are measuring a brightness range from 7 to 10 with
the greycard to 9, you have a very lowcontrast picture. A good transparancy
should take 4 stops (EV 6 to 10) in the detailed shadows and highlights
with the greycard reading at 8.5. Overall contrast is higher of course.


Erwin