Re: [Leica] 18% metering often wrong

[Five Senses Productions <fls@5senses.com>]

Thanks for your excellent review of metering.....now I have a few questions:

Not all films have a DR of 7 stops, right?  Where do you get this info for
each
film you use?

If a reflected meter is not as good as an incident meter for your
technique, how
do you meter a distant scene?  I ask this since a distant scene is too far
away to
actually stand in front of the subject with your meter....right?

I shoot transparency only, usually Fuji Velvia, Astia and Provia, AND Kodak
EPR 64, E100S, and E200.  What do recommend for my situation, shooting
with an M6?  How does one do all this calculation with an M6?  According to
your dissertation, I must carry an incident meter and set the M6 accordingly.

I understand that one can alter development with negative film, but if I shoot
transparency, how can I shoot a 3-SBR scene on 7-DR film and get a perfect
exposure?



At 12:00 PM 4/8/98 -0400, Mike Johnston wrote:
>I can see that we're going to have to do an article on metering. There are
>certainly a lot of misconceptions about it floating around.
>
>18% metering is not accurate metering. It is an approximation--even if your
>meter is calibrated to read middle gray, and you are "giving it" middle
gray to
>meter (such as a gray card, or the grass, or the back of your hand, etc.) 
>
>Why? 
>
>Picture it this way. Say your film will record 7 stops--visualize these as a
>line of 7 gray blocks in a row, with middle gray in the middle, three lighter
>tones approaching white on the "highlight" (right) side and three darker
tones
>approaching black on the "shadow" (left) side.
>
>The problem is that you must match this to a scene. The scene has a range of
>brightnesses as well, which, for the purposes of our illustration, you can
also
>visualize as a "stepped" series of grays--a line of gray blocks, black on one
>end, white on the other. 
>
>If you come upon a scene with a 7-stop range of subject luminances, you're
>fine. The row of gray "blocks" from the scene line up perfectly with the line
>of gray "blocks" that represents the film's range. The problem arises when
>you're _not_ dealing with 7-stop scenes. 
>
>First, let's use as an example a scene that has, say, an 11-stop SBR or
subject
>brightness range (this would be called a "contrasty subject"). If you simply
>find a middle gray area in that scene, meter that accurately, and expose your
>film, you can see what you've done if you "graph" it by lining up the two
rows
>of gray blocks one above the other, with the middle (middle gray) blocks
>matched up. Picture it in your mind. Is it clear that you will still fail to
>record on your film nearly two stops of range on either end of your film's
>density range? This means that some of the shadows will be empty black and
some
>of the highlights will be blank white (blocked up). 
>
>Now imagine a scene with a 3-stop SBR. Again, you find the middle gray in the
>scene and accurately meter it with your 18% meter. The trouble is, now the
>scene is of lower range than the film. So you have effectively "overexposed"
>the film, because you have given the lowest tone in the scene sufficient
>exposure to render it not as the first block on your film's density range,
but
>as the _third_ gray tone in your film's density range--one block to the
left of
>middle gray. 
>
>The basis of the classic Zone System (which is certainly not "extremely
>excellent" but contains a number of inherent errors), is to correct for this
>basically flawed situation by separating the shadow and highlight readings. 
>
>In the first case, with an 11-stop SBR and a 7-stop film DR, you would
need to
>meter the darkest tone in the scene and "place it" congruent with the darkest
>patch of gray in your film's DR. This would require, in our example here,
>nearly 2 stops more exposure than your 18% gray-card reading suggested. Then,
>you would have exposed the film correctly, such that shadow detail would be
>recorded. But your highlights would be way off the scale--3 to 4 stops
over and
>above the film's ability to record them. So what do you do? You curtail

>development to bring the highlight values back down into the film's
range. This
>is called "contraction." 
>
>This is the basis of the expression (coined, I believe, by Loyd Jones),
"Expose
>for the shadows, develop for the highlights." It is also the reason why any
>system which does not allow for individualized development of individual
>exposures is _not_ "The Zone System."   
>
>In the second case, with a 3-stop SBR and a 7-stop film DR, you would need to
>do exactly the same thing--meter the darkest tone in the scene and "place it"
>congruent with the darkest patch of gray in your film's DR. The difference is
>that this time, this results in _less_ exposure than your 18% gray-card
reading
>suggested. But now, the highlights would be registered on the film as a muddy
>middle gray! To compensate for this, you increase development to move the
>highlights back up to where the film wants them to be. This is "expansion."
>
>In the case of a 7-stop subject and a 7-stop film DR, metering a middle gray
>with a meter calibrated for middle gray should yield an accurate, near-ideal
>result. But whenever the subject brightness range varies from this ideal, a
>middle gray reading becomes more or less of an approximation. (This is
also the
>somewhat woeful situation that slide-film shooters are stuck with, because
they
>cannot adjust the DR of their films. They are saved somewhat by the fact that
>color can substitute for contrast in aesthetic effect--as an example,
consider
>that you can get away with a picture that has a large _green_ area that
has 18%
>reflectance next to a large _red_ area that has 18% reflectance, because the
>colors themselves "contrast" with each other, but you cannot get away with
the
>same trick in black-and-white, because the whole frame would be an
>undifferentiated middle gray.)
>
>The system that C.E. Kenneth Mees and Loyd [sic--that's how he spelled it]
>Jones devised in the 1930s is the one we still use today--the film assumes an
>SBR of 7 stops, which they discovered to be the average, and the range of
paper
>grades approximates the expansion and contraction of two stops of SBR either
>way, for correction after the fact of most (not all!) of the typical
departures
>from average. It's a servicable system for rollfilm shooting, assuming
averaged
>metering and averaged development. It works pretty well most of the time.
>
>The Zone System is a whole 'nuther level more accurate. The inaccuracy of the
>classic Zone System is simply that when you change the development of the
film
>to expand or contract its range, you also change its speed point, or the
place
>on the characteristic curve where shadow detail threshhold is reached. Plus,
>the adjustments--the "N numbers"--are not linked to anything real--they're
>simply arbitrary adjustments which hopefully the photographer will apply
>consistently, and learn. So the Zone System, while also serviceable, is
>actually a fairly crude approximation itself. Astute individuals will realize
>that Ansel Adams was already an experienced photographer by the time he
>formulated it, and astute photographers who employ the Zone System will have

>realized that it still requires the application of experience and
judgement.  
>
>Another weakeness of the Zone System is that it relies on reflected light
>meters, which are subject both to flare and to area-averaging. These
reflected
>light meters are _much_ more intuitive for most photographers to understand,
>and hence to use--which is why they're preferred, rather than because of any
>technical superiority--but incident light meters are technically superior
>assuming the photographer has the knowledge and the skill to use them...a big
>assumption.
>
>If you know how the materials really behave, you can expose any scene and
>develop any film and know in advance exactly what grade of paper you're going
>to print the negative on. Phil Davis's "Beyond the Zone System" is the most
>accurate practical exposure and development system in use today, because the
>speed point is automatically adjusted for development and the expansion and
>contraction is stepless and tied directly to the paper you're intending to
>print the negative on.
>
>As I quoted Phil in an earlier post, any exposure meter reading which is not
>based on a shadow reading is nothing but an approximation. It will be correct
>some of the time, and it will be incorrect (to a greater or lesser degree)
some
>of the time. I hope this has helped explain why.
>
>--Mike
>Copyright 1998 by Michael C. Johnston
> 


Francesco Sanfilippo,
Five Senses Productions
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