Expose for the shadows, ....

The instruction to "Expose for the shadows, develop for the highlights." simply guides us to expose the negative long enough to activate the silver halide in the most dimly lit parts of the scene FOR WHICH WE WISH DETAIL ON THE PRINT. The wonderful old SEI Exposure Photometer allowed one to measure either the darkest part of the scene in which some texture is desired (Zone II) , or the lightest (Zone VIII+). It allowed exposure settings for ASA speeds from 1 to 32,000, f/stops from 1 to 32, and shutter speeds from 2 hours and 40 minutes to 1/500,000 second.

If the blue bar represents the range of light in the scene, the negatives will have the following characteristics.

		In this example, too little exposure is given and the lower values in the scene produce zero density in the negative. Most of this negative will be clear, only the middle and high values being recorded.
		By adding exposure, the darkest areas are moved into an area of the curve where differences in exposure create more significant differences in density, thus more contrast or "separation". The clouds are still printable.
		Adding more exposure assures that the shadow areas have the maximum separation. This is wonderful, EXCEPT that the high values in the scene are now bunched together or "blocked" because differences in light make no differences in the negative density. The clouds are now gone and we have a "bald" sky.

The trick is to provide enough exposure to get all of the desired information recorded. If you provide too little light (exposure), areas of the negative will have no "activated" emulsion, and, when developed and fixed, will be clear and void of information. This might lead to a suggestion that you always provide an excess of light (exposure), but each film has a limited ability to react to increased exposure and a saturation point can be reached.

Color and black-and-white negative films tend to have a range which varies somewhat with the film speed, slower films having finer grain and narrower ranges. Each require a different attitude toward exposure.

Historically, it has been good practice to make the least dense negative which included all of the desired data. Increases in exposure tend to exaggerate grain in silver emulsions. Oddly, just the opposite is true for chromogenic (color based, color film and Ilford XP2 Super B&W) emulsions, wherein increased exposure tends to minimize grain. Having said all that, there is still only one BEST exposure for every negative. Your job is to find it!

The image below was made, in the late '70s, from the Vernal Falls Bridge in Yosemite National Park, with a Minox IIIs, and AgfaPan 25 film. It represents my worst nightmare. With a luminance range of ten plus stops, near and far objects, motion that needs to be precisely stopped, AND the requirement for a fine grained film.

In addition, this image illustrates the limitations of the f/16 Rule - "In bright sunlight, normal exposure is 1/ISO at f/16".

In the scene at the left, dark base of the rock meters EV 7 while sunlit white water highlights show EV 171/3. If the exposure is made using the f/16 Rule, placing Zone V at EV 142/3, everything below EV 112/3 (Zone II) will show no texture in the negative and print as pure black. This is fine for scenes with a 6 to 7 stop range and little important shadow detail and is ideal for color reversal film, where overexposure is the worst evil. With negative film, and especially black-and-white, the best, and equally antique, rule is "Expose for the shadows, develop for the highlights." If texture is desired in the dark rocks in the Yosemite scene, an exposure placing Zone V in the EV 11-12 range is required. This is nearly 4 stops more exposure than suggested by the f/16 Rule! Your placement of Zone V will be conditioned by the development scheme (plus, normal, or minus) chosen PRIOR TO exposure as part of the visualization process! It does add a whole new challenge in that - the high values now are hopefully not beyond the shoulder of the film (as here), and control over the appearance of the water is severely limited, and exposure AND development become critical, the latter affecting the former.

BE WARY OF SUNLIT READINGS OF GRAY CARDS! Only a small change in the angle, WILL alter the reading SIGNIFICANTLY! As can be seen, a full 2 stop range was recorded by only slightly moving the card. Reflectivity from the surface of the paper is the culprit! The overhead clear blue sky gives about the same result as the sunlit Gray Card, as will an incident light meter, ...and the f/16 Rule.

So how do you know how much exposure is needed to activate the silver halide in a particular film? The manufacturer will give you a hint, but you should experiment for yourself to find the correct Film Speed for your equipment and technique.