Use Exposure to Enhance Deep Shadows

Boatyard, Maine: The sun was low in the sky and created a strong contrast lighting situation. If this scene had been read with evaluative (pattern) metering the shadow area would have become lighter but all the draama of the light and color would have been lost. To make this exposure in camera a spot meter reading was made off the yellow hull in the background and locked.

While there may be times when you want to expose so that the detail in shadows is “open” and reveals detail, deep, texture- and detail-less shadows can play an important role in composition.  Such shadows can also take on a life of their own and have shape and volume that can be as important to the composition as the visible content itself. They also can break the rectangular frame by spilling into the edges and making curved, triangular and truncated edges.

For this to work the scene contrast must be rather high, or high enough to have no detail or content within shadows when exposure is made to properly expose the highlight areas.

Exposure readings should be made from the brighter or brightest part of the frame alone, with the shadow removed from consideration.  This generally means use of spot metering pattern, or, if the brightness spreads through the frame enough, center-weighted averaging. If need be, a minus exposure compensation can be applied as well.

Tools to Use: Spot metering pattern; exposure lock; exposure compensation.

Artifacts, Cologne, Germany: Made outside the Roman-Germanic Museum in late day light, these artifacts and a post-war building in the background caught the last rays of light. Exposure was made with spot metering off the bright foreground column, which “drove down” the tonal values of the surrounding shadow areas. Standing there I could see detail in the entire frame, but by metering the brightest areas I created an abstract of light and form in the frame. You might want to bracket for insurance and perhaps add +1 exposure compensation when metering bright white areas.

Photos copyright George Schaub

Center-Weighted Metering Pattern

Center-weighted averaging is a bit more “old fashioned” in that it is how light was read, for the most part, before advanced microprocessors got into the mix. The light is read from all parts of the viewfinder, with 70% of the light reading coming from the center of the frame and the remaining 30% of the calculation from the edges of the frame. It is called “averaging” because it takes in all the various brightness levels and then averages them to what is called a “middle gray” exposure reading. This is the basis for much of how metering and translating light value works, so is worth some consideration.

When the metering system receives light from the scene it attempts to average the exposure values so that the bright areas record as bright and the shadows as dark, in essence arranging the light values along a scale of light and dark. Let's say you are working with a scene where there is a range of values, from the bright white in clouds to the deep shadow of a valley. If you read the clouds alone with a spot meter they might read f/11. The edge of the valley might read f/8; the shadow area reads f/5.6. An averaged exposure would be f/8. This “places” the brightest clouds as a highlight, the edge of the formation as the middle value and the deep shadow as quite dark. Thus, exposing at around f/8 places the brightness values as they appear in the scene.

Because the pupil of the camera (the lens opening) is fixed at the moment of exposure, there is no leeway for adjusting to various levels of brightness within the frame. This means that one exposure time has to handle all the lights and darks in a scene, and try to get detail from them all. This is, as you can imagine, a delicate situation. How it is handled is to arrive at an exposure that allows in just enough light to bring detail into the dark areas (the shadows) and not get overwhelmed by the bright areas (the highlights.) This is usually an average of the two intensities of light. The average reading sorts out the lights and darks accordingly so some records as brighter than the average and some darker than the average, as it should be.

Although the exposure system is quite sophisticated you too have to do your part. In essence, the information you “feed” the brain of the meter is the information it acts upon. In exposure that means making a reading by pointing the camera and sometimes locking exposure values to get it right.

For example, let’s say light values EV 11, EV 7 and EV 9 exist in the scene. A change in 1 EV (exposure value) is one stop difference. The average of these three readings is EV 9, which we’ll call f/11 at 1/125 second. That’s the reading the meter will recommend and set for you. EV 9 then becomes the middle gray of the light to dark brightness value, or tonal scale of that image. In essence, the meter has read and set up a range of tones that will be recorded. With EV 9 as the middle gray, EV 11 records as a brighter value and EV 7 as a darker value.

If, however, the reading was made incorrectly and the middle gray was set at EV 7 (which you would get if you just read the shadow areas) then the EV 11 (quite bright) value would record as very bright, and result in overexposure. Conversely, if the middle gray were EV 11 (created if you just read the highlight area) then the EV 7 reading would become much darker than it appears to your eye. All the values work in lock step, so making a bright value a middle gray makes all the dark values darker (and perhaps underexposed, where no detail is seen) and making a dark value middle gray can cause all the bright values to become quite overexposed.

A sunset scene is a classic shot for center-weighted metering. The intent is not to get detail in the ground but to use it as a form that offsets the sky and defines the horizon line. The simplest approach to sunset shots where you want to have a rich sky is to use center-weighted metering, aim the camera at the sky (not the sun!), lock exposure and shoot. Use this method and you’ll never miss a dazzling sunset again.

This might seem quite confusing in the abstract, but working with the camera and making readings exclusively from certain brightness values in the scene, and observing results, will quickly show you how this system works. In fact, you can even make use of this knowledge to create very expressive exposures.

The key to center-weighted reading is to "bias the exposure" towards the highlight. In other words, point the camera towards the highlight area (including other areas as well) and make the reading from that area. This is especially true if the highlight area sits at the corner or out of the center of your framing.

Photo and text copyright George Schaub 2010. In this scene the camera was set on center-weighted metering pattern, pointed towards the brighter area in the upper right, and then exposure was locked and the image reframed to the compositon you see here. Matrix or evaluative would have undoubtedly overexposed the highlights in this scene.

Looking at Scene Contrast

The main issue in making good exposures in high contrast scenes is learning the difference between how your eye “sees” and handles contrast and how the sensor “sees” and records brightness values. Contrast is defined as the difference between the brightest and darkest areas in a scene. In photography the areas that define a usable contrast range are those in which you can see and record detail and tonal values; the compositional decisions often involve how you treat those brightness areas that fall outside this range.

For example, if you photograph a white car in bright light you would want texture and tonal value in the car body and details and perhaps even in the tire tread. But you might not care about the details in the asphalt that sits in the shadow of the car. Or, if you’re taking a portrait in bright light you’ll want good skin tones values in your subject but may not care about information (details) in the shadow he or she casts. When we talk about a usable contrast range we are talking about those areas that you want to record and not those that may also be in the scene but that can fall into tone without detail, like a deep shadow. We can call this usable range of values the "significant" tones, with the brightest in which you want texture the significant highlight and the darkest in which you want detail the significant shadow.

If you take an exposure reading of just the significant highlight you are placing that highlight on the middle of the recording scale—-in essence, you are telling the exposure system that you want the highlight to record darker than it appears in the scene.

And, if you take a reading of just the significant shadow area (like in the image shown here) you will be recording it as brighter than it appears in the scene. This throws off the balance of brightness values in recordings where there are both bright and dark values. If you make a reading of and record the darker areas alone it will cause the brighter areas to “burn up” and become overexposed, just like the side of the building here.

If you want to make a quick test of how making readings from the lighter or darker parts of the scene affects your results, set up a bracketing sequence at +/-2 EV and take three pictures of a brightly lit scene with shadows and highlights. One exposure may average the two values, one will expose for the highlights and one for the shadows. You’ll see how making exposures for just a certain part of the brightness scale affects the other areas.

Photo and text copyright George Schaub 2010. Exposure here was read from the shadow areas. The result in a high contrast scene such as this is fairly substantial overexposure of the highlights, never a good thing in digital (or film) photography.

Exposure: Film and Digital

Exposure is the change caused by light when it strikes a photosensitive material. It has two factors—time (or duration of exposure) and intensity (the volume of light striking that material.) In both film and digital systems the time of exposure is indicated by the shutter speed, the amount of time that the gate through which light travels after it leaves the lens remains open. The volume of the light that gets through in that time period depends on the size of the diameter of the opening in the lens, known as the aperture number or f-stop. Exposure is like turning on a faucet and letting water flow through a pipe. If we leave the tap open for a longer period of time more water will flow through. If we enlarge the pipe more water can run through in that same period of time.

Exposure is calibrated with a system of stops, or the modern equivalent, EV (exposure value). If the total amount of light doubles or halves there is a change of one stop, or one exposure value. A 1 stop or 1 EV change can be made by halving or doubling the exposure time (shutter speed, for example changing from 1/15 to 1/30 second, or from 1/30 to 1/15 second). It can also be changed by opening or closing the lens diameter by one f-stop (for example, by going from f/11 to f/8 or from f/8 to f/11).

This system allows us to expose with the same amount of light and alter image effects by balancing the changes we make in aperture and shutter speed. If we use a faster shutter speed we can freeze motion; if we use a narrower lens opening we can increase depth of field. As long as we maintain a balance between the two (change the shutter speed in proportion to how we change the aperture—one going up one stop and the other down one stop) we maintain the same overall exposure. This setup is called “equivalent exposure” and is the basis for many creative techniques used in photography.

This exposure system holds true for both film and digital photographic systems, as do the image effects they create. As mentioned, the physics of photography do not change because we have gone from a film to a digital medium.