Art 255 Photo Communication and Art 315 Photography, Goshen College

• Learn to count stops from dark to light.  If you can count on your fingers, you can do it. 
• Hold up your hand and spread your fingers. 
• In a NORMAL contrast scene your thumb represents the darkest area of the scene. 
• In a normal contrast scene the gray card reading would be the same as your middle finger.  This would be the reading by which to expose the scene because it is two stops less light than required when metering the darkest part of the scene (a gray card reading is not actually needed).
• In a normal scene your pinkie would represent the lightest highlights.
• Normal contrast is five stops (fingers) and four spaces between

  METERING

II. Meter the lightest part of the scene in which you wish to show textual detail. This reading will be needed in order to know how long to develop the film. The difference between this reading and the reading in the shadow indicates the contrast range in your scene. Keep a record of the both readings (darkest and lightest part of scene) to determine developing time.

NOTE #1: You'll need to use a spot meter or move in close enough to include ONLY the area being metered.  If you don't have spot meter you can select a nearby tone that visually looks exactly as dark as the distant shadow you need to meter.  Maybe meter a dark jacket or something placed nearby so that it looks about the same as a distant shadow area.  Judging the tone may be easier if you squint to eliminate color vision.  If a landscape includes a white building or some very white clouds, it may be feasible to meter off of a piece of white paper to determine the highlight.  Tipping the paper up and down can make a difference in the light it catches, so make it look similar to what you see in the distant scene.  If not using a spot meter, get the camera close enough to the tone so no other tone is seen in the viewfinder.  No need to be focused.

NOTE #2: All frames being developed together will need to be about the same contrast range in order for this system to be useful. Use very short films or individual sheet film so that each film has only one contrast range.
 

EXPOSE FOR THE SHADOWS (zone system rule)

Set camera for two stops less light (less exposure) than the shadow reading and take the picture. Example: If reading is f-11 at 1/125 second, take the shot at f-22 at 1/125 second or at f-ll at 1/500.  Film has the ability to capture information even though this portion is two stops darker than the camera setting.

II. If you metered more than 4 intervals (more contrast) you should reduce the developing time of the film (N -time). This decreases negative contrast. An example of N-1 would be a metered range of tones from f-4 to f-22 while keeping the same shutter speed (six or more finger situation).

III. If you metered less than 4 intervals between the lightest and darkest area, you will need to increase developing time (N+time). This increases negative contrast. An example of N+1 would be a metered range of tones from f-4 to f-11 while keeping the same shutter speed (four or less finger situation). 

How much to change the film processing TIME

Change the developing time 20% per stop when increasing or decreasing contrast. These are estimates.

Examples for less contrast:

N - 1 STOP would require 8 minutes if the normal time is 10

N - 2 STOPS would require 6 minutes if the normal time is 10

Examples for more contrast:

N + 1 STOP would require 12 minutes if the normal time is 10

N + 2 STOPS would require 14 minutes if the normal time is 10

See Upton, chapter 13.

GENERAL PRINCIPLE to use even when not using the Zone System 

If the light is bright and harsh, like a bright sunny day, overexpose and under develop for better negs. Set the camera to 50 or 25 when you are using 100 speed film. This will expose the shadows better. Process the film 20 to 40 percent less time to keep from stopping up the highlights in the negs.

If the light is very flat, like a very overcast day, underexpose and overdevelop for better negs. Set the camera to 200 when you are using 100 speed film. This will expose the shadows okay if the lighting is very soft and gray.  Process the film 20 percent longer to increase the density of the negatives in the highlight areas and improve the contrast range.

Compared to negs made conventionally, these will be a joy to print. Try it. 

WHY DOES IT WORK?
HIGH CONTRAST SCENES
Think about the light hitting the film.  Strong highlights penetrate down way down into the emulsion and expose lots of silver halide particles.  Weak light from shadows just barely exposes a few particles on the outer surface of the emulsion.

In a high contrast scene (metered automatically) the shadow areas get essentially no light because shadows lack enough light to get the silver even on the surface exposed.  However, by exposing within two stops of the darkest shadow (zone system rule) there will always be some light to expose a bit near the front surface of the film's emulsion (film allows for this much latitude).  Naturally the highlights will get very overexposed in this situation.  Therefore, cutting short the processing time corrects this by not allowing enough time for the developer to soak all the way into the emulsion of the film.  The overexposed part of the scene remains undeveloped.

LOW CONTRAST SCENES
By exposing within two stops of the darkest shadow (zone system rule) there will always be some light to expose a bit near the front surface of the film's emulsion (film allows for this much latitude).  In a low contrast scene this will leave the highlights somewhat underexposed, but even so, the developer will, if allowed to work long enough continue to work on the exposed particles until they darken the negative sufficiently.  The shadow areas of the film do not continue to develop during these extended times because the effected particle are all near the surface and do not require any amount of time for the developer to soak down to them.  This is why longer developing increases contrast.