The four basic exposure strategies.
In the field, landscape photography can be broadly divided into two tasks, the job of finding a compelling composition, one that is worth photographing, and the equally testing matter of exposing the newly discovered scene correctly.
In photography circles, the issue of composition is a particularly popular conversation point, with the rule of thirds, leading lines, symmetry and patterns all being examples of strategies that one might employ in pursuit of a masterpiece. The subject of exposure, by contrast, is a decidedly less glamorous topic and is often abjectly branded as a ‘technical discussion’.
A tough composition but an even tougher exposure.
However, let’s assume for a moment that you are walking in the great outdoors and stumble across a shaft of light that is illuminating the world’s finest example of the rule of thirds; What do you do? What is your strategy when it comes to exposing for this compositional marvel?
The first step, of course, is to understand what is meant by a ‘correctly exposed’ photo. A correctly exposed photo is one that manages to capture all the detail in a scene with no overexposed highlights or underexposed shadows. All the information on offer is captured, in its entirety, within a single image.
The trouble is that the ideal exposure is often not possible. Landscape photographers in particular are frequently faced with satiations where the highlights and shadows in a scene far exceed those that their camera can capture in a single frame. To account for this difficulty, what is needed is a set of strategies that allow photographers to cope with various lighting scenarios all of which ultimately result in the prized ‘correctly exposed’ photo.
Strategy 1: Low contrast scenes – Let the camera handle it.
A low contrast histogram with all the available information fitting comfortably within the diagram's limits.
In many instances, modern cameras are more than capable of relieving photographers of any exposure-angst. Provided that the scene in front of you doesn’t contain very bright highlights or very deep shadows, there is a good chance that the camera’s own light metering system will do a perfectly good job of calculating the correct exposure values for you.
Low contrast scenes are characterised by a histogram that features all the data bunched together in the middle of the graph. If it happens that data in the histogram is off to one side, then a small amount of exposure compensation should be all it takes to get the histogram correctly positioned in the centre, and the photo properly exposed.
It is worth noting that if the data does not fit comfortably within the bounds of the histogram, then the scene you are trying to photograph is not a low contrast candidate.
An example of a low contrast scene with no significant highlight or shadow areas.
Strategy 2: Higher contrast scenes – Protect the highlights.
An example of a higher contrast scene histogram with some highlight information being lost on the right edge of the diagram. This is a perfect candidate for highlight protection techniques.
As the difference in brightness between the highlights and shadows grows, so the task of correctly exposing becomes a more challenging undertaking. The camera’s metering system is likely to start making significant calculation errors as the image data begins to fill or even slightly exceed the bounds of the histogram.
Under these circumstances, the preeminent thinking is to protect the highlights, ensuring that the data on the right-hand side of the histogram (the highlight data) stays within the right-hand limit.
Doing so may mean that some of the shadow detail is lost as it falls below the lower limits of the histogram, but having a few black pixels in the photo is widely seen as more favourable than areas of the image being white and completely overexposed.
A higher contrast scene featuring deep foreground shadow areas; the result of a highlight protection strategy.
Strategy 3: High contrast scenes – Use an ND or double up.
With a moderate amount of information loss in the highlights, and a lot of shadow detail present (making highlight preservation techniques ineffective) this histogram is well suited to strategy three.
Sacrificing shadow detail can only get one so far, though. As contrast increases even further stil and image data spills out beyond the boundaries of the histogram, large tracks of the photo will begin to turn black if photographers persist with highlight-preservation techniques. Instead, what is required is a way to improve upon the native capabilities of the camera so that all the detail can once again be captured. There are two common ways to do this:
- Photographers can make use of neutral density (ND) filters. ND filters allow part of a scene to be selectively darkened while the rest remains unaltered. This makes it possible (in certain situations) for the highlights in a scene to be darkened while the shadows remain unchanged. This may be all it takes to see the image data within the bounds of the histogram once more.
- The alternative is to take two photos, one correctly exposing for the highlights and the other correctly exposing for the shadows. Using layers and masks in Photoshop, it is then a relatively straightforward exercise to blend the two images and to produce a final product with all the detail present.
The important thing to remember, though, is that both methods work best when the highlights and shadows present in a scene are only just beyond that which the camera can capture on its own. Anything more and these rather crude blending techniques will result in obvious transition zones or, worse, a photo with a fake look to it.
Graduated neutral density filters can be a valuable tool when dealing with high contrast scenarios.
Strategy 4: Extremely high contrast scenes – It’s time for HDR.
With enormous amounts of data lost in the highlights and a strong shadow component too, this histogram represents an extremely high contrast scenario.
If a fake look makes your stomach turn, then high dynamic range (HDR) photos have the potential to make you feel outright nauseous. However, there comes a point where the contrast present within a scene exceeds that which even two photos can contain. In these extreme situations, multiple images are required, with each one having a different exposure setting, something that makes image blending a far more intricate affair.
A typical example of an HDR process includes taking three photos, one 1-stop underexposed, one ‘normally’ exposed and one 1-stops overexposed using a camera’s Auto Exposure Bracketing (AEB) function. The three images store an enormous amount of image data with a tonal range that extends well beyond that which any single image might contain. Applications such as Adobe Lightroom’s HDR Photo Merge facility can then be used to combine the images into a single data-rich file.
Since HDR files, in most cases, include far more data than a camera can capture and, occasionally, even more than the human eye can resolve, working with the files can be an artistic balancing act. There is a fine line between creating an HDR image that looks compelling and one that looks like the product of 60s psychedelia.
The product of a high dynamic range strategy with the foreground shadow almost entirely eliminated despite the existence of very bright highlights.
Parting thoughts.
If there are two things to take away from this superficial dive into exposure strategies, it is the following. First, it is not how bright or dimly lit a scene is that determines how one goes about exposing; rather, it is how much contrast is on display. Sure, overall light intensity determines the aperture and shutter speed settings that one might use but it is contrast which will determine what detail can be captured and what can’t.
Second, taking the perfect exposure is just as much about selecting the correct exposure settings in the field as it is about knowing what can be done with those exposures once you’re back at the computer. In many cases today, getting the perfect shot means many hours spent finding the scene and many hours in front of the screen.
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