The Goldilocks Principle in Photography
In the children's story of the Three Bears, Goldilocks repeatedly finds that one possible choice, whether it be beds, chairs or porridge, is too big or too much, another is too small, but the third choice in between these is just right. I've been noticing how the same principle holds true for a number of choices at the heart of photography.
First though, let's acknowledge that the influence of this principle isn't limited to fairy tales and photography. It's a subtext influencing choices often in daily life. That's clearly why the story of Goldilocks has remained so popular all the years. The moral and practical implication of choosing what is "just right" is a common theme. But what got me thinking is the degree to which such choices lie at the very core of photography. An appreciation of this basic theme can help make you a better photographer.
If I'm trying to capture the sunrise over Mt. Rainier with a field of alpine wildflowers in the foreground I want to achieve the greatest depth of field possible. If the wind isn't perfectly calm though, there is such a thing as too much depth of field. Maximum depth of field requires stopping the lens aperture way down and increasing the exposure time to compensate. But if the shutter remains open any time at all, some of those beautiful wildflowers are sure to move in the wind and spoil the shot. On the other end of the range of choices though, a shutter speed fast enough to ensure any possible motion will be frozen in time also guarantees I can't use an aperture small enough to get the depth of field I want. Unless I can afford to come back on another day when there is no wind, a compromise is necessary. One aperture is too small as it will result in motion blur. Another aperture is too big as it won't give me enough depth of field. What is needed is an aperture that is "just right," one that will hopefully optimize all these variables.
Of course on a digital camera you can also change a third variable: the ISO setting. Every sensor has a native ISO" that reflects its true sensitivity to light, and this value will certainly be at or close to the slowest ISO the camera is capable of. Many modern cameras do remarkably well at higher ISO settings too, allowing the user to break the two-variable reciprocity relationship between shutter speed and aperture. To a point, you can have good depth of field and a fast shutter speed simply by increasing the ISO sensitivity. But there are limits. At some point, every camera will suffer from enough noise to make shooting at that stratospherically high ISO more bother than it's worth. Yes, you can capture the image with everything in focus, and without motion blur from the wind, but at the cost of a grainy image from high ISO noise. Of course sometimes photographers will shoot at the slowest ISO their camera is capable of simply because they think they have to. But this may so slow that they deprive themselves of a workable range of options for aperture and shutter speed. By raising the ISO at least some, their options for these other two exposure variables greatly increases. In other words, some ISO settings may be too small for the task at hand, while others may be too big. What is needed is an ISO sensitivity that is "just right," yielding high quality results still free from noise while providing exposure flexibility and working latitude.
A good image must also have sufficient resolution. An image shot with an inexpensive point and shoot camera may be good enough for many uses but will likely fall short of professional standards for the discriminating viewer. It simply won't have enough megapixels to record the detail needed. But cameras with the highest megapixel counts are also the most expensive cameras. It costs a lot to produce such sensors as well as the chips and circuitry necessary to process and store the images it produces. Everyone's needs and budget won't be the same of course, but no matter what yours may be, there's likely some number of megapixels that will be too low to get you good enough images, and also some megapixel count that will at least stretch your budget. And of course some range of megapixels that will be "just right" for your situation and needs.
The physical sensor size matters too. There are limits to how many megapixels can be crammed into any given space. Eventually the wavelength of light itself becomes a limiting factor. All things being equal, a larger sensor will be capable of higher resolution images than a smaller sensor will be. This is both due to how many photosites can be fit on the head of a pin, but also due to the quality of signal that can be recorded by photosites of differing sizes. Bigger ones capture more light and are therefore more immune to random signal noise than smaller ones crowded onto smaller sensors. And bigger sensors tend to result in bigger, heavier cameras. If all your shooting is done in the studio, size and weight may not be a factor, but if you have to lug that camera up a mountain trail to get the shot you are after, saving weight can be extremely welcome. Exactly what size sensor or what size and weight camera best fits your needs is something only you can work out, but once again, there will be some that are too small, some too big, and hopefully at least something that will be "just right."
There are numerous other examples as well. Small memory cards are cheap but require constant swapping out as they fill up with while larger ones are more expensive per gigabyte. Small gamut color profiles such as sRGB can be easy to work with yet large gamut ones such as ProPhoto RGB can produce more vivid results but can be harder to stay out of trouble while using. You get the idea. No doubt you can think of more if ponder it a while.
Everything in photography seems to be a tradeoff. There's simply no such thing as an inexpensive, compact camera capable of world class results under all conditions. Especially those of us that shoot mostly outdoors have a lot of factors beyond our control to contend with, and thus a lot of tradeoffs to solve. These factors all have consequences. While they may pale in comparison with being eaten by three bears who find you in their house eating their porridge and sleeping in their bed, they are real enough when you're trying to get good images. Understanding the tradeoffs that govern the photographic process and how picking a possible answer for one influences your choices for other decisions is an important part being a successful photographer.