Lighting & Composition

Photographing Flowers: Focus and Sharpness

Being “in focus” is only one aspect of whether a flower photo appears sharp. I’ll get to the other factors that lead to the appearance of sharpness in a moment, but first I’d like to step back for a second and ask whether sharpness is always a good thing.

Logically speaking, there are three possibilities: a flower image can be end-to-end sharp, it can be unsharp everywhere, or the image can combine areas of sharpness with areas that don’t seem sharp. Furthermore, even overall sharpness is not an absolute, but rather a matter of degree. It’s not uncommon for us to say to ourselves, “This photo looks a bit sharper than this other one.”

In other words, to some extent sharpness is subjective.

My idea when photographing this calla lily was to make the flower seem sharp— particularly its calyx, the sex organ in the middle of the flower—but to make sure the flower appeared isolated compared to the background. Placed against a white background, the flower appears almost architectural, with flowing and undulating curves. Photo: 300mm, 36mm extension tube, 1/10 of a second at f/16 and ISO 400, tripod mounted

There are famous photographers who have believed that only completely end-to-end “tack sharp” photos are true art. But I don’t subscribe to this viewpoint. Sharpness is not a moral issue. Furthermore, unsharpness itself can be an attractive compositional element, particularly when it comes to flowers.

But you should know how to make flower photos sharp, and if you choose not to make them sharp, it should be exactly that—a choice.

With this perspective in mind—that sharpness, or lack thereof, is one of the visual elements you can and should control when making portraits of flowers— let’s take a look at focus, sharpness, and the causes of unsharpness.

With this close-up view of an iris, I wanted a “conventional” high depth-of-field view with the petals of the flower all in focus, so I stopped the lens down as far as I could to f/40. Photo: 105mm macro, 10 seconds at f/40 and ISO 200, tripod mounted

Obviously, if you don’t focus precisely, you risk losing sharpness. Flower macro photography can present particularly difficult focusing conditions, so you may wish to use a magnifying eyepiece to help you see whether your target area is actually in focus.

If you want your photo to be unsharp, throwing the camera completely out-of-focus is a good way to go about it.

As I previously explained, stopping down the lens to a smaller f-stop increases the depth-of-field, and therefore increases the range of distances within a photo that are in focus. You may wish to bear in mind, however, that the optimal optical sharpness of most lenses is from 2 to 4 f-stops from the maximum aperture. So, for example, a lens that opens to f/2.8 at its widest aperture will be optically sharpest at between f/5.6 and f/11, not when it is stopped all the way down to f/36. In other words, increasing the depth-of- field can lead to loss of optical sharpness due to diffraction, although in my tests I don’t tend to find the loss of optical sharpness that large an issue.

This is the same calla lily as the one shown above, except I posed it on a black background before photographing it. It is interesting to compare how the different backgrounds affect the look and mood of the photos. With the black background, the flower seems more mysterious, as if the lily was revealing hidden secrets. Photo: 300mm, 36mm extension tube, 1/4 of a second at f/16 and ISO 200, tripod mounted

Motion—either of the camera or your subject— leads to blurring. This can sometimes be an interesting effect, but if you want to avoid it you’ll need to use a good tripod, work to avoid camera shake, and avoid flowers in a breeze—or use a fast shutter speed.

The optical quality of your lens of course impacts sharpness, and if you are looking for unsharpness you can use this to your advantage in many ways. Special purpose lenses such as the Lensbaby are engineered to allow sharpness only at a “sweet spot”—with attractive out-of-focus areas taking up the rest of the photo.

You can also put a filter coated with Vaseline over your lens, or shoot through something in the foreground such as moving grass or translucent fabric.

Oddly enough, one of the best ways to make an element in a photo seem really sharp is to use selective focus—meaning to set your lens aperture and focus point so that just the desired element is in focus. The contrast between an element that is in focus and a background that is not tends to make the in-focus element look sharper than it would if the entire photo were in-focus.

The out-of-focus areas in a photo have a quality all their own that is sometimes referred to as bokeh. Whether you use selective focus or throw an entire image out-of-focus, the quality of the bokeh in a photo varies widely depending mostly on the lighting and the construction of your lens. Of course, if you intentionally shoot through fabric or some other substance to create a soft effect, the nature of what you are shooting through also controls the look of out-of-focus areas.

Selective focus on this strawberry flower conveys the sense that the strawberry is in the process of forming; a partially in-focus image with the “sweet spot” of focus carefully chosen tells this story better than a fully in-focus image would have. Photo: Lensbaby, +10 close-up filter, 1/200 of a second without an aperture ring at ISO 200 (effective aperture f/2.0), hand held

Excerpted from Photographing Flowers: Exploring Macro Worlds with Harold Davis by Harold Davis © 2012 Taylor and Francis All Rights Reserved

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