ONLINE DIGITAL PHOTOGRAPHY COURSE

LESSON 3 - DSLR Camera Techniques, Part 2
(Exposure Control - Using the Light Meter)
Article by Stephen J. Kristof
© 2010, all rights reserved


"O.K., so now I know how ISO, f-stop and shutter speed can independently impact exposure... But how on earth do I know what combination will provide a proper exposure?

This is where an invaluable feature called a "light meter" comes into play!

The Importance of the Light Meter

One enormous advantage that Digital Single Lens Reflex (DSLR) cameras have over their less expensive and easier to use "point-and-shoot" counterparts have is that DSLR's have the all-important light meter built-in and, most importantly, VISIBLE to the photographer. Without a visible and fully-interactive light meter, manual adjustments to any of the exposure controls are just guesses. While the pros do their fair share of "bracketing" (taking multiple shots at different exposure settings), they don't like to take blind guesses, because time is money

Instead, pro photographers use the light meter to help make an educated decision about what they believe will be the most suitable combination of exposure variables for a photo shoot's particular features and challenges. They will then often try some neighboring f-stops and/or shutter speeds on either side of their initial decision as a form of insurance, because occasionally these bracketed exposures provide a better image with, perhaps, improved color tones, richer darks, sharper contrast, brighter whites and/or better detail.

The avid photo enthusiast and the pro alike may also use their years of experience to occasionally ignore the reading that a light meter is providing when he or she realizes that the meter is limited in that particular situation. Overall, though, professional photographers rely on light meters to help them make these very important exposure decisions. They routinely use the camera's internal light meter as well as hand-held light meters that provide a more accurate measure of the ambient or incident light in the environment and image frame.

The internal light meter inside a DSLR will do a fine job of measuring the brightness or luminence of light reflected off the surface of an object (called "reflected" light), but does not do a good job of measuring the existing light that falls upon a entire shooting environment (called "ambient" or "incident" light).

On a hand-held light meter (left), the incident light creating the general ambience of the scene is often measured using a diffuser that looks either like a glass honeycomb or a half ping-pong ball; either one of which gathers the "general" lighting of the environment.

 

"I don't have a light meter like the one shown above, but my D-SLR does have an internal one. But, what do the numbers mean and how do I use it?"



How to Read and Use the D-SLR's Internal Light Meter

By now, you should realize that this section applies to the photography learner who wishes to explore MANUAL settings on the camera. The great thing about shooting using manual settings is that you regain control over various technical decisions that the camera would otherwise make for you, while empowering the creative scope of your photographic expression. Understand that the camera's full-auto setting as well as the various programmed settings (such as "backlight correction", "portrait", "sports", "dusk" and so-on) are nothing more than a set of instructions based on rather vague parameters that may or may not reflect that specific conditions or creative goals under which you are shooting at any particular moment.

In other words, the camera's auto mode may well result in a perfect exposure one time, but not the next. Understanding how the light meter works will allow you to make more informed decisions regarding your choice of ISO, shutter speed and f-stop settings that are ideal for the context. Moreover, you'll know how to use the light meter's recommendation based on YOUR goals rather than the camera's auto-interpretation of what it thinks is an ideal outcome.

Consider this example; you are strolling along a shoreline or pasture looking west over the expanse of sea or land that lies beyond. The sun begins to set and with it, the sky is ablaze in deep hues of orange, red, azure and even notes of purple. Fortunately, your camera is at the ready and as you dial the power wheel to the "auto" setting you anticipate just how stunning the image will be.

However, in spite of your best framing, your camera produces images that leave much to be desired, because when you review them on the bigger "viewfinder" of your computer monitor, your photos appear rather washed-out without the appealing rainbow of saturated colors.

"No problem," you think, "I'll go back tomorrow and if the sunset Gods are willing to put on another show, I'll use my camera's program mode for such a situation - the "dusk" or "sunset" setting."
 
The next day, the sunset does, indeed, cooperate and you do exactly what you had planned, using the program setting. Regrettably, when you review this second set of images on the viewfinder, you see that the sky has a bit more vibrance and color, but, again, not to the degree you had expected, nor do they approach what you see before you in the sky itself.

This is a very real and often-experienced disappointment that could easily have been corrected, given an understanding of how to properly read the camera's light meter and how to "override" or bracket its recommendations based on an expanding knowledge of exposure control and photographic techniques.

So, what went wrong?

Specifically, the camera's auto and program settings will widen the aperture and/or slow down the shutter speed, allowing more light into the camera to compensate for the darkening sky. The problem with this robotic decision is that the brighter exposure will invariably wash-out the beautiful colors in the sky, thus negating the "sunset" look you wanted to capture. Had you read the internal light meter reading, you would have realized that it would have been a good idea to purposely underexpose the image by closing the aperture somewhat or increasing the shutter speed. The decreased exposure would have enhanced the saturation of colors, leading to a spectacular sunset photograph.  Occasionally, the auto setting may do the opposite, basing an exposure decision on the sun itself (if visible and above the horizon).  In this case, the camera may respond by underexposing the image too much, thereby making the image far too dark.

The examples below compare the usual result of auto exposure (left) to that of a slightly underexposed manual exposure (right).

 

 

Most photographers that developed their skills using traditional film-based SLR cameras came to rely on the floating vertical needle that was the internal light meter.  Unfortunately, if you're in that group, don't expect that old relic to reappear anytime soon!

These photographers were (and continue to be) disappointed in the over-simplicity of today's horizontal LCD metering icon and many continue to miss the responsiveness, ease of reading and accuracy of the old needle.  In fact, the old 'relic' was a wonderful tool and its demise was a real loss.

Click here to begin the next course unit, DSLR Camera Techniques, Part 3 - Exposure Control and the Light Meter Revealed.  You will find some visual examples of today's digital internal light meters and see first-hand how they work.


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