Saturday, September 15, 2012

The Science of Photography -- Part One

People tend to draw a line between “art” and “science.” They think there is some kind of fence between the two subjects that trap people in either one of the other arena. I hear a lot about “left-brain” and “right-brain” as if that was a physiological explanation of the separation. Just as some people are right-handed or left-handed, they will often describe themselves as right-brained or left-brained.

Broad generalizations are often made in popular psychology about one side or the other having characteristic labels such as "logical" vs. "creative," ”analytical” vs. “intuitive,” “number” vs. “rhythm,” or “sequence” vs. “synthesis.” However, these labels need to be treated carefully. Although a lateral dominance is measurable, these characteristics are in fact existent in both sides, and experimental evidence provides little support for correlating the structural differences between the sides of the brain with functional differences. There is a lot more “excuse” than “science” to people who self limit themselves with such explanations.

Certainly I’ve dedicated most of my life, my career, and my education to “science.” And I really doubt I have much of a talent for art, although one must confirm definitions before making such limiting statements. I would likely fail that famous drawing test from the “Match Box School of Art,” although I suspect everyone who draws the pirate, even as a stick figure, gets accepted into the school as long as they can pay the tuition.

Besides, science has plenty of visualization and perspective and creativity. Much modern art is very scientific and well engineered buildings and bridges can be beautiful works of art.

I was brought up in a home where music was always being played and performed, and I’ve enjoyed music all my life as I’ve attempted to create some. I found my skills and talents were more in the area of capturing and recording music, but that has not slacked my appreciation and enjoyment nor my own personal playing.

There are several other artistic endeavors I’ve engaged in, including the art of writing which I’m attempting before your very eyes. I’ve recorded music and video, I’ve produced music and video, and I’ve created music and video. But I think the closest joining of art and science is in still photography. Photographs can be hung on the wall like any fine art and they seem to link the present with artists from long ago.

But, on the other hand -- or side of the brain -- photography and cameras are scientific instruments, and even the greatest artist must obtain knowledge and skill to use the instrument well. So it is a marriage of art and science, a beautiful marriage indeed.

I think photography is the closest, high-technology implemented “fine art” that I perform. After all, a photograph is very akin to a painting, and expressionism or other schools of art can be implemented in a photograph too. But, as you gentle readers know, my largest pool of skill and knowledge is in the scientific realm. So, with that introduction, let me start what I expect will be a very ambitious project where I tell you everything there is to know about camera science.

I suggest you get a comfortable chair. Possibly put on some soothing music. Now settle back for a long read as I describe the scientific principles behind photography. These are the principles that apply to both film and digital photography as I explain the basic rules of physics and how they apply to the photographic art.

Focus and Exposure

There are two primary attributes that must be manipulated and controlled in the production of any photograph, be it on film, or digital, or any other type of image capture using optics (lenses).

The first is focus. That is a function of the lens or set of lenses as they bend light and produce an image on the image sensor and the distance to the object being photographed. The sensor may be a light sensitive chemical coated on what we call “film” or a light sensitive sensor in what we refer to as “digital photography.”

Exposure describes the amount of light gathered relative to the sensitivity of the recording medium, either film or a sensor.

Controlling exposure is a combination of lens function (aperture) plus shutter function (speed) combined with the sensitivity of the sensor (ISO). Interestingly, exposure control can also affect focus. So lets start with exposure control and how lenses are designed and adjusted to effect the amount of light focused on the sensor.

Of course, the amount of light focused by the lens also depends on the amount of light on the subject, the thing -- person, scene, flower, etc. -- being photographed. And that opens another whole area of art and science such as the light from the sun vs. light from a lamp vs. flash, etc. And there are other scientific areas that photography involves such as the science of color and reflection and many other areas a fine artist attempts to control and capture when taking a photograph.

Both film and digital sensors can have varying degrees of sensitivity to light. In the case of film it depended on the chemical process and was described as a number standardized by the International Standards Organization called the “ISO Number.” (Older photographers will recall the ASA and DIN measurements which have been combined in the modern ISO standard in 1974.) With digital sensors it can be controlled electronically by adjusting amplifier gain and is also described with an ISO number.

But first, I want to focus (no pun intended) on the control of exposure. After all, a good photographer must know how to control exposure in order to correctly capture the great variation of light that may exist. In my personal opinion, everything starts with exposure control.

What a photographers must do is to set their exposure using a combination of shutter speeds and f/stops to get the correct amount of light on the film or sensor. The shutter speed regulates how long the sensor or film is exposed to light coming through the lens. The f/stop regulates how much light is allowed through the lens by varying the area of the hole the light comes through.

For any given film speed (ISO) and lighting combination there is one correct amount of light to properly expose the film. This amount of light can be achieved with many different combinations of f/stops and shutter speeds.

Despite being one of the exposure controls in photography, the f/stop remains a source of confusion and mystery to many photographers, even to some who use it all the time.  Although I take pride in being terse and laconic, I think what is needed here is a long-winded discussion of f/stop where I tell you everything there is to know about the topic. So lean back in that comfortable chair, here it comes.

(See part 2 for a continuation of the discussion.)

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