Among the least understood technical aspects of photography, at least for novices, is aperture. Yet aperture has profound effects on the resulting image. Consider the following series of photos, each taken with a macro setup of an MP-E lens on a Canon dSLR camera, focused at the foremost tip of an ant head head shot at increasingly smaller apertures:
What’s going on?
Most lenses contain a diaphragm that can constrict from full open down to a little hole, controlling the amount of light that travels through the lens on its way to the film or sensor. The size of the hole is called the aperture. It is measured as a fraction, such that an increase in the denominator signals a decrease in aperture. F/8 is four times smaller than f/2.
As the aperture is decreased (or “stopped down”) the amount of light decreases, allowing a photographer to make use of slower shutter speeds. Relevant to insect photography, smaller apertures also extend focal depth. More of the subject appears in focus, a key property considering the razor-thin focal planes that plague the tiny realm of macro. Here’s an example using a lady beetle:
Most insect photographers shoot at small apertures (around f/9 to f/16 or so), maximizing focus over the broadest depth possible. This is mostly where I work too, as a deep focal plane is ideal for illustrating behavior, morphology, and other aspects of biology.
Yet for aesthetics we should also consider the blurry, dreamy realm at the full-open end of the spectrum. One of my favorite photographers, Rick Lieder, works exclusively wide open using ambient light, and his results are stunning.