Capturing Images

more in Capturing Images

The objective of all serious photography is to gain control of the camera and, to whatever extent possible, the environment in which it is operated. You will find it as equally important to position for light and background as to manipulate exposure functionality. When we got underway, exposure and composition plagued us for months. Creating the best exposure of a subject means learning to read light, not only intensity but also how it casts shadows, including the impact it will have on movement or color extremes. This will take some time and experience to grasp. In this synopsis, we try to summarize the fundamentals of various exposure techniques and provide hints on the basic rules governing good composition.

As previously stated, we would recommend that you don't let post-processing techniques let you get "sloppy" when it comes to taking the best exposure possible. If your camera body is so equipped, activating the Highlight Alert feature provides a quick visual confirmation of exposure problems. However, the histogram is the bible. Overexposure is skewed right ("blown" whites) and underexposure is skewed left ("blocked" blacks).

For now we would also recommend that you use Auto White Balance only, especially if it is a sunny day. The AWB setting is preferable to using one of the presets as they use fixed values for color temperature. If the ambient light is not at the specified value, the image will have a color cast that may render even enhancement impossible. It can be argued that Custom is the best choice, but this entails manually setting up an index using either a white or 18% grey card under a range of different lighting conditions. This is probably best left for later experimentation. However, see Ian Lyons at Computer-Darkroom if you pathologically want to attempt this technique early on. We generally shoot some quick test pictures before starting a session, using either the internal meter (a reflected light method) or a separate Incident Meter (a direct light method) to gauge the appropriate aperture and shutter speed for the prevailing lighting and movement conditions. A quick check of the histogram for "clipping" tells us whether any micro adjustments are necessary. Adjusting White Balance for "effect" is best left for downstream processing and is simple to adjust in most RAW converters.

To us this is an endless and completely subjective topic as most of our tastes differ radically when viewing what is essentially, at least at the professional level, an art form. There are, however, some basics to achieving a good perspective. The first is to divide the viewfinder into nine quadrants. The four intersecting "power points" are recommended as good subject placement locations as centered perspectives more often than not produce the least dynamic results. This concept is known as the "Rule Of Thirds." Second is to position at subject eye level and utilize a background with uniform tonality such as grassland, open water or sky. Less homogeneous back drops can often be enhanced by "opening up" to achieve a satisfying background blur. Positioning should attempt to eliminate foreground and background distractions such as habitat that will interfere with placing the subject in a dynamic perspective (branches and horizons are usually the major culprits). You should be particularly aware of "hotspots" such as wet surfaces or bare branches that generally produce harsh reflections in full light. Difficulties with distractions can often be eliminated by recomposing for a portrait of the subject. Capturing a head turn, especially with eye contact, is the pinnacle of success. Arthur Morris has produced an instructive article on this subject "Guidelines For Advanced Composition And Image Design," that should still be available in the Naturescapes Archives.

For beginners, there is nothing more daunting than understanding exposure. Generating the "best" exposure begins with metering. This is how the camera sensor visualizes light and interprets color. It is important to recognize from the outset that the built-in meters of digital cameras measure "reflected" light, interpreting all colors as midtones. However, colors are usually more vivid in nature and the tonal contrast between subject and backdrop is invariably quite stark. If we've learned anything since the advent of digital camera technology, it's that even though metering has slowly improved it can be mediocre, even at the best of times. A good quality camera body usually offers a number of metering choices, of which the most important for our purposes are Spot and Evaluative. Before we explain how to use each, it's best to review the three key fundamental settings that must be made to create an exposure: ISO; aperture; and, shutter speed.

To begin, you need to set an ISO value that's commensurate with the prevailing light and subject movement. You can now gain total creative control of the two remaining variables in Manual Mode or rely on the camera to determine the final one by fixing either aperture or shutter speed in Aperture Priority Mode or Shutter Priority Mode respectively. We're assuming you will bypass the fully automatic settings. After all, photography is all about taking control of the camera. All you need is a little practice. The following are some generalizations that will help you get started.

ISO choice is simply a function of the quantity of available light given subject movement. For Canon users, an ISO of 200-320 is sufficient for wildlife photography in clear and sunny conditions where motion is not a mitigating factor. Under these conditions, we usually start at the higher setting and quickly check the histogram. A flight shot, under similar lighting, is best achieved at a high shutter speed which in turn usually demands a higher ISO setting. Here we generally start with a value of 400 or slightly higher. If light is really low, such as only early dawn or late dusk can produce, a setting of 800 or higher is recommended. However, high settings in some camera bodies can produce a soft or "grainy" image known as "noise." In our experience, this is usually not a problem with the Canon product line offered today. Most modern "prosumer" camera bodies such as the Canon EOS 5D Mark III have ISO settings up to 25,600 or higher, including an Auto ISO feature. Moreover, noise issues are now relatively easy to resolve through the use of Photoshop plug-ins such as Topaz Labs DeNoise 5.1. Notwithstanding, experimentation is the key to success.

The aperture choice or size of the opening that emits light onto the camera sensor is described by a series of "f-stops" associated with the focal length of the lens you are using. An example of full f-stop increments would be 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 and 22. Most quality digital cameras provide f-stops between the above numbers, usually in 1/3 or 1/2 stop increments. Thus you may find f/6.3 and f/7.1 between f/5.6 and f/8. In general, your aperture choice depends on the amount of subject sharpness or depth of field you are trying to create. The lowest number represents a fully "open" setting, emitting the maximum amount of light and creates the least depth of field. As you "stop down" by choosing progressively higher f-stop numbers, the opening narrows, creating a greater depth of field. Conversely, as you "open up" by choosing smaller f-stop numbers, less depth of field is produced, creating background blur. This, of course, is exactly what you are attempting to achieve when photographing birds in a contrived "perch" setting where the subject must be sharply defined on a background that significantly reduces detail, a subject we treat in our Field Tips synopsis. In general, f/8 is a neutral setting producing good results in most static situations. Moving one or two full stops higher or lower produces greater or reduced depth of field respectively. This of course depends on how far away the subject is and the magnification of the lens you are using. If the subject is close and you are using a long lens to compose a portrait, you will have to stop down quite a bit to create sufficient depth of field to capture detail from nose to ear. The rule of thumb is that depth of field is roughly equivalent to 1/3 in front and 2/3 behind the focus point. If you are photographing a small bird with a long tail that faces away from your camera position, it is probably wise to choose a higher f-stop in order to capture more tail detail. Experimenting at varying distances with different subject sizes and orientations will soon make your choice of aperture a much more intuitive exercise.

Choice of shutter speed, or length of time the available light is allowed to remain on the camera sensor, is simply a function of motion and the degree to which you can hold the camera steady. How fast is fast? In the worst conditions where light is low and the subject is relatively comatose, you can get away with a slow shutter speed, usually in the order of 1/50 to 1/150 of a second. However, you will need extremely steady hands or a tripod at these levels. Flight shots, on the other hand, must by necessity freeze motion and require settings usually in the order of 1/1250 to 1/2000 of a second to achieve a good result. Again, a little experimentation will soon make these decisions obvious.

As we have said repeatedly, finding the right combination for all three settings to produce the best exposure possible takes practice. There is little solace in recognizing that most bird and wildlife photography involves trade-offs as the available light invariably doesn't match the movement or depth of field issues you are trying to solve. Flash can compensate somewhat but is often problematic to implement "in-habitat" unless positioning is relatively easy to achieve. As we consider flash a stressor, we tend to restrict its use.

For those wanting a quick start, under exacting conditions, "sunny sixteen" is a good rule-of-thumb to keep in your back pocket. Here you set aperture to f/16 and shutter speed to 1/ISO providing it is a sunny day, the subject is a midtone color and your shadow is directly in front of you. If the subject is predominantly black or white, you would use f/11 and f/22 respectively. This is an old rule that stands up well when you want to analyse a quick test shot and continue to make hasty adjustments in the interest of time.

Now that you have a basic understanding of the three prime variables that must be determined to create an exposure, it's time to add a fourth dimension - metering. In our opinion, all the foibles of exposure center on metering. Depending on the situation, we use three metering techniques to help establish our exposure settings.

The first, and a method we always use in snow or on subjects where a gray tone is prominent in the frame, is the Spot meter. This is an incredibly easy process to implement yet counterintuitive to understand. We start by setting the ISO and shutter speed for the prevailing light and subject movement. As the Spot meter utilizes roughly 3% of the total frame and is center oriented, the objective is to meter off a neutral color on or near the subject and then adjust the aperture until the meter as seen through the viewfinder is centered. Alternatively, you can meter off a dark or light color and underexpose or overexpose starting at 2/3 of a stop respectively. The trick is to learn what colors work best. Here's an example. A male Plains Bison is standing in a light yellow grassland setting in full sunlight. You could meter off the neutral brown of his hump (zero the meter), off his black behind (underexpose by 2/3) or on the light grass (overexpose by 2/3). So what's counterintuitive? By underexposing a dark color you're simply telling the exposure algorithm to lighten up a bit! This makes sense as the Spot meter interprets any color as a midtone. Although the process is easy, it does require practice, especially for determining the appropriate color to meter. We find this method best for relatively static situations where we have a bit of time to experiment with test exposures.

A Spot meter is built-in and measures reflected light, requiring a good sense of color to use successfully. An easier method is to employ an external Incident meter that measures the direct light that falls on a subject. Incident metering eliminates the need to recognize and adjust for tonality differences as direct light measurement renders the midtones and contrast exactly as seen. There are many Incident meters on the market with varying degrees of functionality. The Sekonic M358 is a cost effective choice that does the job in spades. And it's easy to use. Simply input ISO for the prevailing light, aim the instrument in the direction of the subject with the measurement globe facing you and take a light reading. Turning the dial will give you an array of appropriate aperture and shutter speed selections. Choose the one combination that is appropriate for the situation and input into the camera. Here's an example of just how easy this is. On a clear and sunny day, under front light conditions, we guarantee the Incident Meter at ISO 200 will recommend 1/800th of a second shutter speed at an aperture setting of f/8. This will give you a perfect exposure for most relatively static situations and once experienced you won't have to take this light reading again. Moreover, if you suddenly want more depth of field and stop down to say f/11, simply count the clicks on the aperture wheel to achieve this and move the shutter speed wheel the same number of clicks in the opposite direction. This will again produce the correct exposure. Alternatively, if you want more shutter speed, adjust the dial the appropriate number of clicks then move the aperture wheel the same number of clicks in the opposite direction. What could be simpler!

A third method, and the one we employ most often, is Evaluative metering, Here we use either Aperture Priority Mode or Shutter Priority Mode and employ the Exposure Compensation feature to fine tune our settings. This is a technique that is essentially the opposite of the one we use when Spot metering. Here's an example. A white Mute Swan is basking in full sunlight in a water setting. We've chosen ISO 320 and f/8 in Aperture Priority Mode and need to meter for the camera to determine the appropriate shutter speed. Like the Spot Meter, Evaluative also measures reflected light but now utilizes the entire screen. It's an algorithm that searches its data base for a shutter speed setting that is appropriate for the color array it is trying to interpolate to a set of midtone values. Here's the rub! It can't adjust for the harsh reflection off the white, forcing you to underexpose 1/3 to a full stop using the Exposure Compensation wheel to ensure you capture the feather detail in the swan. Conversely, if the Swan were black, you would need to overexpose by a similar amount. If the subject and setting are mostly neutral in color, no compensation would be required. It's a method we have used with good success but again requires practice.

As you can see, digital exposure theory has few variables and some nuances but the basics are fairly easy to grasp. Moreover, there is absolutely no reason to begin using an enhancement program such as Adobe Elements, Photoshop or Lightroom until you can master producing good exposures.

more in Capturing Images