As an instructor of over 400 photography workshops, lectures and seminars for almost eleven years, I’ve witnessed a practically unanimous change from film photography to digital photography as the choice of the image capture medium. Rarely do I see a roll of film or film cameras in the hands of my many attendees. It’s practically nonexistent and the debate once associated over the fate of film at the hands of digital is dead too.
Photographers have come to accept digital is here to stay, it’s an evolution, not a revolution and in that acceptance, most photographers lost focus of how equipment has evolved with this now common medium of capture. As an example, a new photographer will never know that an aperture ring with numbered aperture values (F/stops) once existed on lenses. Most of the more veteran photographers haven’t noticed the ring is missing and if they have, they just take it for granted as they’ve become accustomed to all the values and settings along with “chimping” and viewing the histograms on their LCD displays and the LCD panels on the camera tops for verification of those settings.
The irony of all the displays, from the rear LCD screen to the top of the camera screen and even the screen in the viewfinder is that the effect it’s had on photographers parallels how society tends to lose its customs, values and traditions as new family generations adapt to their surroundings—similar to a sociological pattern change, humans adapt.
This adaptation has caused photographers to forget the meaning of that aperture ring and why the ring had values like 1.4, 2.8, 5.6 and even 8 and eleven. That ring, and the actual numerical values are all based on the Inverse Square Law.
Now it’s not uncommon if you ask any photographer, even top professionals, on the spot, to explain the Inverse Square Law that they will stop to think and most of the time tap dance their way out of the conversation though they truly understand and practice that physics law we apply to photography. I myself stumble when unexpectedly asked to cite the Inverse Square Law verbatim, but I have a method that always bails me out—the aperture ring on my lens. The problem is all my new lenses have no aperture rings except the lenses for my Leica M-8 digital rangefinder.
Regardless whether you own a Leica lens or a lens with an aperture ring, the concept is simple, aperture values are based on the Inverse Square Law and that is why a lens has a few numbers with decimal point values like 1.8, 2.8, and 5.6 and not 2, 3, 5 as whole number values.
In the old film days, we’d look at our lenses and always understand that the difference between F/2.8 and F/4 is one stop of more light (50-percent brighter) in one direction and 50-percent less light in another direction (darker). While those aperture values helped us understand light passing through a lenses and striking the film plane, we also understood that the higher the aperture value the more depth-of-field we’d gain in our images and smaller the aperture value, the less depth-of-field we’d gain from the focus point.
Yet there was another purpose of that aperture value ring on our lenses, it could actually help you calculate the effects of the Inverse Square Law simply by looking at the dial and understanding the correlation of those numbers with the subject to light distance or the light to background distance. As an example, if I had my model four feet from the main light source illuminating her for my photograph and decided she was one stop too dark in the exposure, I’d merely move the light in so that the distance between my model and the light source was two-feet, eight inches (think F/2.8). If the condition was in reverse where my model was too bright by one aperture value at four feet, I’d simply move my subject from the light source so the distance would equal five-feet, six-inches (think F/5.6). This in fact is the Inverse Square Law. In fact if my subject was two full aperture values too bright, I’d ensure the distance between my subject would change from the original value of four-feet to eight-feet (F/8.0).
The same holds true for controlling our backgrounds, if we have our model four-feet from the main light source and the model is four-feet from the background, and expose correctly for the model, the background is then receiving two stops or aperture values less of light to illuminate it as it’s eight feet from the light source in total distance. If I decided I wanted to brighten the background one F/stop, I’d simply keep the same distance from the main light source to my subject, four-feet in this case, but ensure that the background is now five-feet, six-inches from my main light source and of course if I wanted the background another F/stop darker from the original eight-foot distance, I’d make sure my background was eleven-feet from my main light source.
Now that aperture rings are almost gone from lenses, we see on our digital camera LCD screens aperture values like 5, 6.3, 7.1, 9, 10, etc. and unfortunately the correlation of those numerical values and the Inverse Square Law seems forgotten.