There are a couple trains of thought about the use of depth of field in macro photography. One camp insists that one should stop the lens aperture down to gain the most depth of field so that the entire image is as “in focus” as possible. The other camp insists that a very shallow depth of field works well to isolate a subject. I tend to follow the second example although there are good reasons to use both. Let’s take a look at them.
Shallow depth of field can isolate the subject by putting the background and foreground out of focus. We achieve this by shooting at wide apertures (f4for example) and focusing precisely on the subject. The focus point is critical. When photographing an insect you need to focus on the eye generally, with flowers quite often it will be the petals but in other instances it might be the stamens. Let’s look at a few examples:
I think most of you would agree that the first image with the lovely out of focus background is the best image, but is this always the case? The closer we get to the subject when doing macro photography the less depth of field we have for a given aperture. On very small subjects this often means that the tip of a stamen might be sharp but everything else is out of focus and guess what, this doesn’t always work. We are in a position of compromising the sharpness of the subject with the softness of the background. The choice of background can make a huge difference here as well as the focal length of the lens. I’ll cover this in another article.
When would we want to use the maximum depth of field possible (small apertures)? If it is important to have the complete subject sharp and the subject has depth you might be forced to shoot at small apertures to achieve this. By watching the background closely at least you can minimize the distraction. Dark backgrounds and light backgrounds can help immensely as can very simple backgrounds. Another option is to show as little of the background as possible by getting in really close to the subject.
A few other options are possible; if you can keep the camera plane parallel to the subject you may not require as much depth of field. If you do require that little bit of extra depth of field watch the background carefully and be willing to shift the camera a fraction to make the background work for you. Consider the background a compositional element even though it’s not your main subject. The photograph of the yellow Brittlebush flower shows this well. Special rails are available for this purpose although they tend to be bulky and expensive.
A last thought. What I have been discussing with macro work also holds true with almost all other photography and especially photography with long telephoto lenses. Take a look at those amazing sports photographs that the pros are shooting of ML baseball or many of the excellent wildlife images; they have very soft backgrounds isolating the subject by using limited depth of field. Here are a few examples.