Proper Exposure

There is no such thing as a precise definition of proper exposure because it is an inherently subjective matter. This is because an image is properly exposed if and only if the exposure is the way you, as the artist/photographer, want it to be.

Yes, I know, in and of itself, this is not very helpful, but it is nonetheless true.

Keep in mind, that as the photographer, you are the creative artist making the images, and that necessarily means that it is you, and only you, who should have the final word on how the image looks. This is not to say that there are not photographic or image standards; rather, it means that as the artist in charge you are the one who chooses how to apply (or disregard) them.

Be that as it may, most photographers who are attempting to create images that approximate what they saw generally think of proper exposure as recording the amount of light required for the image to exhibit good detail in the darkest shadows and in the brightest non-specular areas. (Specular areas are pure white regions that contain no detail, such as highlights on a reflective metal surface.)

For a number of the photographers, especially those who did not shoot reversal (slide) film, exposure is not a conscious issue because they just set the camera to auto and shoot. This can work reasonably well when there is relatively little contrast within the frame and the scene/subject is mid-toned. The reason for this is that virtually all light meters provide settings based upon the assumption that your subject is a mid-tone. That means your meter assumes your subject is reflecting the same amount of light as an 18% gray card would reflect, even when using evaluative, sometimes called matrix, metering (which I do virtually all of the time).

Not surprisingly, this is often not the case. Consider, for example, that you are photographing a breeding plumaged Laughing Gull on a white sand beach or against a bright sky. Your meter will give you a reading that is likely to blow out the whites in the gull, sand, or sky; or darken the image to such an extent that the black hood and mantle of the gull will be featureless. (The differing results depend upon the lighting and the size of the subject in the frame, among other factors.) Further compounding the situation is the fact that the quality level of much of today’s photography has become decidedly mediocre as a result, in significant part, of inexpensive cameras, the ease with which camera processed images (JPEGs) can be uploaded and distributed, and the failure of many photographers to want to improve the quality of their work.

There is also the all-too-common attitude that most, if not all, photographic problems can be fixed in Photoshop. While it is true that Photoshop and other image editing software are wonderful for enhancing images, it is just as true that few problems can be fully corrected in them and those that can require much more time and effort than getting it right in the camera. For example, if I were to over expose an image to the point that little or no detail were recorded in highlight areas, there is nothing that any program can do to recover data that were not recorded. Likewise, if I were to underexpose an image but not so severely as to have no detail, correcting the exposure with software would almost certainly result in a significant increase in noise. (Noise comes in two types: color and luminance. Color noise is the presence of off-color pixels while luminance noise is the presence of overly bright or overly dark pixels.) Always keep in mind that a basic rule of digital photography is to rely on Photoshop, or any other image processing software, as little as possible!

Achieving a proper exposure is a matter of balancing the three exposure variables: ISO, shutter speed, and aperture. However, achieving the desired result requires knowing what you want and balancing these variables in order to achieve this end.

I suggest that you first decide on the ISO you want to use.

Most of my photography is of birds and, typically, I want to capture them doing something. This means I need to stop their action. This is one area in which digital is far superior to film. With film, I almost never used an ISO higher than 200. With digital, my normal ISO setting is 500, and I am not reluctant to shoot at an ISO of 6400. Although these higher settings can produce noise, it is relatively minor given the cameras I use (Canons 7D and 1D Mark IV). The reason I choose such a high ISO is so I can shoot at a small aperture to increase the depth of field. (Depth of field is the portion of the image, front to back, that is in focus.)

I often want my subjects to be large in the frame. One of the realities of this is that the larger the subject in the frame, the more shallow the depth of field. This is especially true when you use long lenses with teleconverters, as I frequently do. Thus, I use a relatively high ISO in order to allow me to use a smaller aperture with its associated greater depth of field.

However, if I were shooting a stream and wanted to create an image in which only the water was out of focus, I would use a low ISO. This way, even with a small aperture, which would cause the non-moving parts of the image to be in focus, the moving water would be blurred with a slow shutter speed. (This, of course, would require that the camera be mounted on a tripod.)

As you can see, there is no formula for choosing an ISO. You, as the photographer, must know what you want to create and then select the ISO most likely to help you achieve it.

Once I have decided on my ISO, I then have to decide the camera mode I want to use. Usually, for the work I do, this is AV, which stands for aperture value. What this means is that I determine the aperture I want to use, and the camera then decides which shutter speed to use. Just keep in mind that, as the photographer, I have the option of altering the camera’s choice.

For example, if I am shooting a mid-toned scene/subject in full sunlight, I am likely to use the settings the camera offers. On the other hand, on a cloudy/overcast day, the camera is likely to select settings that will underexpose lighter than mid-toned scenes/subjects so I add light via the camera’s exposure compensation function. Conversely, on a cloudy/overcast day, the camera is likely to select settings that will overexpose darker than mid-toned scenes/subjects so I subtract light via the camera’s exposure compensation function. How much light I add or subtract depends upon the conditions and the size of the subject in the frame. When I shot film, I would make my best guess and then take a series of photos making some a little brighter than I thought would work and some a little darker. I then had to wait until I received the developed film back to see if I made the right choice, and with no realistic option to correct any mistake.

Digital photography makes this a much easier process because of the histogram function included in most of today’s digital cameras. Thus, after I made my best guess/judgment, I check the histogram to see if I was correct. If so, fine; if not, I make another adjustment and check it again. (I will explain how to read and use histograms in a future posting.)

Again, my goal in shooting birds usually is to capture them doing something (not just sitting there), and often against a non-distracting background. A good way to do this is to shoot against a smooth, pleasing, mid-toned background. However, if this background is close to the subject and I use a small aperture, I run the risk of having enough detail in the background for it to become a distraction. Thus, I like to have a significant separation (20 feet or more) between my background and my subject. As a result, I prefer to shoot with an aperture of f11 to f16, depending on the lens, subject, and other factors. Paramount among these other factors is shutter speed, because I still want to freeze the subject’s action. If, for some reason, I cannot separate the subject from the background, I will use a larger aperture (smaller f number) to reduce the detail in the background.

Again, you as the artist/photographer have to decide what it is you want to achieve and then choose the aperture most likely to produce these results.

Not surprisingly, choosing a shutter speed is no different.

If you are trying to freeze a bird in flight without panning (moving the camera to keep the subject in the same position within the frame), you typically need a shutter speed of 1/2500 of a second or faster! In other words, you may have to raise your ISO and/or open your aperture depending on the light. However, by panning you can slow the shutter to freeze the action so long as you are able to keep the subject in focus. While this has been made significantly easier with state of the art autofocus technology, it still requires practice and choosing a shutter speed that will facilitate the desired result.

For panning flight shots, I like to have a shutter speed of at least 1/2500 of a second.

I also do a fair amount of bird photography from blinds. In such situations, I prefer to create a limited number of perches in front of pleasing backgrounds and near feeding or water features. In situations such as these, I will often use a shutter as slow as 1/125 of a second.

Again, one of the big advantages of digital photography is the ability to take an image and almost immediately review it. True, to see it well it must first be downloaded to a computer, but the LCDs on the back of mid to high-end DSLRs give a reasonable in-the-field view so that you should be able to get a decent sense of whether or not you are using a faster enough shutter speed.

In conclusion, you and only you are the artist/photographer and, as such, it is your responsibility to balance the exposure variables of ISO, aperture, and shutter speed to achieve the exposure you desire.