In the already absurdly problematic world of ‘exposure’, it seems almost cruel that the first tone adjustment slider to confront the Lightroom user is itself called Exposure. As if there isn’t already enough said about aperture, shutter speed and ISO, now there is a fourth exposure control to be concerned with and the obvious question must be, How does this Exposure adjustment fit into the much-publicised domain of the exposure triangle?
Before you begin fiddling, as one might, it is essential to understand that Lightroom’s Exposure adjustment, as well as its close relative, Contrast, are unlike all other tone adjustments. Uniquely, changes to these two adjustment sliders influence every single pixel contained within the unwitting image, a marked difference from the other lesser sliders which have their pixel-pushing powers explicitly restricted. The Whites adjustment slider, for example, has its authority limited to only the very brightest pixels in a photo and the Blacks slider, likewise, affects only the very darkest. The global pixel reach of the Exposure and Contrast adjustments is so unique, in fact, that Adobe bestows upon the two sliders the great privilege of sitting atop a thin grey line in the Tone adjustment group.
Being a cut above the rest, in this case, is more than merely symbolic, though. As a global adjustment, Lightroom’s Exposure slider exhibits significant parallels with exposure in the aperture, shutter speed and ISO sense of the word. Increasing your exposure by way of rotating any of the Aperture, Shutter Speed or ISO knobs that adorn your camera has the effect of increasing the brightness of the resulting picture as a whole. Visually, at least, the same generally brightened result could be retroactively achieved by moving Lightroom’s Exposure adjustment slider to the right once that image has found its way into the computer.
As uncomplicated as the explanation may perhaps seem, photography is never quite that straightforward. The trouble is that adjusting a camera’s exposure settings at the moment of shooting does considerably more to a photograph than simply manipulate its brightness. Varying the aperture has the further effect of altering depth of field while shutter speed impacts upon the way that any motion present in the scene is captured. In reality, the camera setting that best mimics the illuminating exploits of Lightroom’s Exposure adjustment is ISO. Changing a camera’s ISO has no noticeable bearing on the composition of a photograph whatsoever; it only effects the all-round brightness. For a particular aperture and shutter-speed setting, dialling up the ISO makes the resulting image brighter and dialling it down makes it darker, precisely the same action as the enigmatic Exposure slider, and the relationship doesn’t end there.
The similarities between Lightroom’s Exposure adjustment and ISO extend further to include the shortcomings of both parameters as well. Raising a camera’s ISO has the less-than-desirable side effect of elevating the level of noise within an image and the same is true when increasing the exposure in Lightroom too. Noise always steals a march when something other than the presence of more photons is responsible for making a picture brighter. In some sense, the humble slider and the camera’s ISO are in the business of artificially influencing brightness. They both have the cunning and wizardry necessary to make things lighter when the light itself has gone unchanged; a feat which translates directly into noise.
Noise is a contentious subject in photography circles; one often cited when comparing the products of one manufacturer to those of another. The increased post-processing latitude that cameras with improved noise performance create is beyond dispute. However, if we work under the assumption that we all wish to get the most from the cameras that we own, then comparing one model to another is all a bit meaningless. The truth is that any increase in exposure resulting from tinkering with Lightroom’s Exposure slider is a step away from image quality, regardless of any specific camera’s technological prowess. Nothing supersedes getting the exposure right when the camera is in your hand and it is this point that sits at the heart of questions attempting to relate the Exposure slider to the venerable exposure triangle.
Lightroom’s Exposure slider can, for all intents and purposes, be viewed as little more than a retrospective ISO adjustment. It is a tool jam-packed with all the same pixel-brightening goodness of the original ISO setting along with all its nasty side effects too. The overarching goal whenever one takes a photograph is to meet the exposure and compositional requirements necessary to capture a scene, while using the lowest possible ISO setting. Achieving this rather lofty goal ensures that you have created an image which represents the very best that your camera can produce. Any effort to make up for missing this goal by using the Exposure slider comes at the unnecessary cost of quality. Consequently, for all those making their first steps into the world of image processing, be it using Adobe Lightroom or any other application for that matter, my advice is, as far as possible, to steer clear of the Exposure slider. It looks like a saving grace but really isn’t one at all!