Botanical Macro Photography
Photographing plants in their natural settings takes a bit of practice. Plants can’t run away and hide, so they seem like easy targets. But most are always in motion, even in apparently still air. Flowers are often bright against a much darker background, presenting exposure challenges. Plants are often enmeshed in a tangle of other plants, making it hard to distinguish the subject from its surroundings. This article presents some techniques for getting good close-ups of plants.
Camera Types. There are several camera types in common use today:
This photo of bishop’s caps was taken with a point-and-shoot camera in macro mode. Each flower is only about a quarter inch across. The smaller sensor’s deeper depth of field is evident, because the house in the background is about 20 feet distant, and in relatively sharp focus.
ILCs produce better results than point-and-shoots, but require more practice and more expensive gizmos. This article is about ILCs. They come in two flavors: those with “full frame” sensors (same size as traditional 35 mm film) and those with smaller sensors about 2/3rds as large. Both have unique advantages and both produce great results. The smaller sensor gives you about a 50% increase in magnification and deeper depth of field. The larger sensor provides more resolution. I usually use a macro lens, a 60 or 100 mm, for close-ups. If I am close to the subject, I use flash to isolate the foreground subject, to freeze motion, to eliminate white balance problems for more accurate colors, and to bring out surface texture. Flash also avoids the need for a tripod.
But the results are less than perfect. Frequently the plant shows a bit of motion blur. Flash is supposed to freeze motion, so where does the blur come from? Turns out it is a result of how shutters work.
Shutters and flash. A shutter contains a curtain that opens to admit light to the sensor.
When you take a photo, the curtain slides aside to allow light to pass to the sensor. In reality, the curtain is composed of many overlapping segments so that it doesn’t take up much space when open.
But there’s a problem. The end of the sensor furthest away from the curtain gets light for a longer time than the other end does, so the exposure won’t be uniform. This is easily solved with two curtains though.
First, the camera opens one curtain completely while the second remains closed. Next, the first curtain closes while the second opens, so they are both moving in the same direction.
At the end of the exposure, the second curtain is closed, and each part of the sensor has received the same amount of light.
But curtains are mechanical, and mechanical things can only move so fast. It takes about 1/60th of a second to open or close. If a shorter exposure is needed, the curtains are operated a bit differently. Here, we get a 1/120th second exposure by starting to close the second curtain when the first is only half open. This moves a band of light across the sensor that illuminates each part for 1/120th of a second.
To get very short exposures, such as 1/1000th of a second, the two curtains are closer together, admitting only a narrow slice of light.
This approach works fine for natural light, but the rules change radically for flash. Xenon flash tubes produce a brief, intense flash lasting as little as 1/40,000th of a second. So if we set the camera to a 1/1000th second exposure, the flash fires for such a short time that the curtains barely move during the flash interval. Thus the flash illuminates only the narrow band the curtains are over at the moment of discharge. The result is a stripe of light against an otherwise black background. Not good.
Thus the camera must be set to an exposure time that is long enough for both curtains to be entirely open at the time the flash fires. This is somewhere between 1/60th of a second and an absolute minimum of 1/320th of a second, depending upon the camera. We’ll call this the minimum flash shutter time, or just the minimum. In a dark room, a minimum exposure doesn’t let in much of the natural light because there isn’t much around. But in a sunlit setting that’s a very long time. Using a flash in daylight produces two images in one: a minimum exposure made in natural light, plus a ≈1/10,000th second exposure from the flash. This can be a good thing if the subject is still, because the flash fills in the heavy shadows in a sunlit scene. But if the subject is in motion, this is bad. The minimum is enough time for the flowers to sway in the wind, so the photo shows motion blur, like this.
The first strategy to combat motion blur is to close down the aperture and admit less background light. Instead of shooting at, say, ƒ/8, shoot at ƒ/22. The camera should also be set on its minimum ISO, since this reduces light sensitivity and improves image quality. These steps accomplish three important goals at once. First, they reduce motion blur as we discussed. Second, they isolate the brightly lit subject from the darker, more distant background. Third, they increase depth of field: more of the close-up image is in focus. With macro lenses, depth of field is sharply limited, making it very hard to get much of the plant in focus. (Purists maintain that closing down the aperture that far introduces diffraction blur that limits sharpness, but this effect is modest relative to the benefits.)
Wait! We’ve set the ISO, the aperture, and the exposure time by hand. Isn’t that ... dare I ask? ... manual mode? And isn’t manual mode for fanatics? Well sort of, but manual mode is the simplest solution to the problem. When using flash we have to set the exposure time to whatever is recommended by the manufacturer, say 1/250th of a second. It is always best to use the manufacturer’s minimum recommended ISO, which typically varies from 50 to 200. All that leaves is the aperture, and we have already seen reasons to set that to a specific value as well.
Ring flash. There is another problem with macro. In most cameras, the built-in flash is positioned for normal use, not close-ups. Built-in flashes may wash out their subject, or may even be partially eclipsed by some macro lenses. Add-on flashes may be sharply angled away from the camera’s line of sight. (If you have such a flash, you can mitigate this with a diffuser.) Ring flashes with xenon flash tubes are a better alternative. A ring flash mounts a couple of flash units aside the end of the lens. The light from these units is exactly where you need it, and most ring flashes allow you to adjust the intensity of each flash separately. You can use light from only one flash to emphasize texture, for example, when photographing coins. For plants, I get very nice results with both flashes enabled.
Ring flashes are a bit awkward and a bit fragile. But for macro they excel. I settled on a Sigma unit rather than a similar Nikon, for three reasons:
(Update: The Sigma flash is no longer available, and when mine wore out, I got a closely similar Meike MK-14EXT TTL Macro Ring Flash. It works very nicely too.)
LED-based flash units are cheaper, but they produce a much smaller amount of light for a longer period to get the same total amount of illumination. This means they cannot freeze motion like a xenon flash. LED flash units may fire for as long as 1/5 second, easily enough for camera or subject motion to cause blur, and weak enough so that outside light overpowers the flash. Hence they are unsuitable for this kind of work.
Focus. Many macro photographers prefer manual focus, since depth of field is so limited that careful attention to focus is critical. I pretty much agree with this, but I rely on autofocus nonetheless. I disable the autofocus function that focuses when the shutter button is half-pressed though. Instead, I press a separate button to focus, called AF on Nikon bodies. This brings the lens close to where I want it. Then I simply move the entire camera back and forth a short distance to select the most suitable focal plane. Occasionally I can be seen, head bobbing back and forth like a cobra’s, trying to follow a swaying plant.
Macro lenses. Why bother with macro? The features necessary to reliably identify plants are usually small, even on large plants like trees, and there is no substitute for a clear, magnified image. Besides, there is a great deal of beauty just below the usual threshold of our attention, and close-ups reveal it. About 99 out of every 100 of the photos I take employ a macro lens.
Most macro lenses magnify about the same amount: 1:1, meaning the image on the sensor is actual size. So how do you choose a lens? Nikon makes four sizes, for example: 40, 60, 105, and 200 mm. These focal lengths determine how far you must be from your subject to achieve a given degree of magnification, not how much magnification you can achieve. Most people prefer the 105 mm, but I usually shoot with this 60 mm Nikon Micro-Nikkor lens.
It means that the closest point of focus is about 3 inches from the end of the lens, a problem if your subject is a white-faced hornet’s nest. But it also means that the light from the flash is so close to the subject that it swamps background light, producing perfectly frozen images. Also, a 60 mm is wide enough to double as a normal shooting lens. A 105 mm lens increases the closest shooting distance to a foot or so. A 200 mm increases it further, to several feet, at the expense of added weight.
Extension tubes. These hollow tubes of various lengths move your lens further away from the image sensor, providing more magnification. However, depth of field is even more limited, and the optics are imperfect, so I don’t use extension rings in the field. But if you are photographing small items such as seeds indoors, you can use extension rings to get higher levels of magnification. (How can a hollow tube have imperfect optics? It can’t. But lenses are designed to function optimally at a fixed distance from the sensor, so some distortion is introduced when you alter this distance.)
Macro focusing rails. You can obtain finer control over focus using macro focusing rails, adjustable screw drives upon which you mount the camera. Don’t scrimp through—inexpensive macro rails like this one from Adorama lack precise enough control.
The Cognisys StackShot Macro Rail Package is at present the Rolls Royce of macro rails, a precisely controlled motorized macro rail that can be operated by the included controller or by host software on a computer.
You program it by picking a starting and ending focus distance, and an increment between. The StackShot then takes multiple photos, even 100 or more, moving ahead a tiny distance between each. The resulting images are loaded into a computer and focus stacked, using software such as ZereneStacker. This means that the subject must be absolutely static during the sequence of photos. That rules out most herbaceous plants and even mosses, which wilt quickly. Grasses, seeds, and lichens often work well. This isn’t a great choice for field use, since it is awkward to set up, and requires AC power unless you rig up a battery source. I use it at home.
Depth of field. Getting the “right amount” of depth of field is a challenge for all photographers. A portrait photographer might choose narrow depth of field intentionally, to highlight a person’s eyes while softening their face. A sports photographer might do the same, getting a soccer player in sharp focus while softening the audience in the background. But for macro photographers, there is never enough depth of field. This is the biggest single limitation on macro photography, and the reason why even higher magnification lenses are rarely sold. The closer you are to the subject, the more limited the range of distances that appear in perfect focus. With a 60 mm lens on a full frame sensor, you may only have a centimeter or two of depth that is in focus. (Longer lenses improve on this a bit.)
You can improve depth of field in several ways:
Exposure. Flowers are meant to attract pollinators, and most of the tricks plants use to do that attract our attention too. But those bright flowers against a dark background also confuse the exposure meter. Cameras usually calculate exposure based on the entire scene, but for flower photos it is usually best to enable “spot metering” and center the spot over a flower. Typically, I:
Here’s where it gets tricky though. When you spot meter on a target, you are telling your camera “this is the item that should come out in the middle of the brightness range,” not “this is something bright.” That means that if the flower fills the whole region the meter is watching, you will underexpose the flower and way underexpose the background. If you see underexposed photos, you can turn up the exposure compensation, use center-weighted metering instead of spot metering, or spot meter on a spot that also includes some background. (Center-weighted metering is simply a bigger spot.) There is no substitute for practice here.
Raw shooting. Lots of people insist that the exposure and composition should be perfect before you shoot. Balderdash! I’m often huffing up a trail, hanging off a tree over a sharp drop, balancing on a squishy boardwalk over a bog, or walking with my dog on her leash in one hand and a walking stick in the other. My wife is a hiker, intent on covering ground, not fussing over botanical photographs. So I’ve learned to shoot from the hip, figuratively at least, and sometimes literally. I always shoot in raw mode. The much increased dynamic range of raw mode provides much greater control when I use Adobe Lightroom later to compensate for what I didn’t get right in the field.
Pixels. I haven’t said a word about pixel counts because everybody lusts after megapixels, but few of us need them. They are good for when you need to blow images up to poster size or larger, something most of us have little call for. But high resolution is also useful for increasing magnification, or cropping out parts of an image that are distracting. So I get as many megapixels as I can afford. Here is a photo of a flowering grass and a full-resolution crop from it.
Carrying gear. A heavy camera gets old fast after hanging around your neck for a few hours, and it flops around as you walk. Backpacks are too slow to deploy if you take a lot of photos. Neck bags just add weight. There are harnesses that hold the camera closer against your body, which I have not tried. My preference is a well-engineered belt holster called a SpiderPro Single Camera System. You screw a metal pin into a plate that attaches to the tripod mount, and use the pin to hang the camera, upside-down and pointing backwards, from your hip. This sounds almost comically awkward, but it works unbelievably well. In one fast motion I can remove the camera from the holster and pick it up, where it is then facing forward for a shot. This also means that the back of the camera is facing forward when it is holstered, so if the camera brushes against obstacles it is much less likely to be damaged. I have used this holster extensively and I am a big fan.
Composition. My goal is to help people identify plants, so I try to capture at least two identifying characteristics in each photo. This ties together important features in the viewer’s mind. For example, leaves plus the pattern by which they connect to stems, or older and younger leaves, or flowers and the supporting structure under the flowers. I also try to isolate the plant from its surroundings, though this is often nearly impossible. Sometimes surroundings help. An acorn or pine needle might serve as a aid to determining the size of a mushroom. But too much simply confuses the eye. Try to take side views, not just top views. Take at least twice as many photos as you need and discard half.
Because depth of field is so limited, try to find camera orientations that put several features of interest in the same plane of focus. A triplet of flowers, taken from an angle that puts all three in focus, might look more appealing than a spray of flowers that are mostly blurred.
Picking up roots. Sometimes the simplest solution to a difficult shot is to pluck the plant and put it somewhere that lets you photograph it. There are times when this is the only practical solution. But it almost always produces disappointing results. Plants continuously hoover up water from their roots and pass it out through pores in the leaves, in a process called transpiration. It is this internal water pressure that keeps the plant rigid. Most plants quickly sag when picked or uprooted, looking deflated and sad. They don’t look like themselves any more. So I do this only as a last resort, for example, when there is something important about the roots, or when the plant is best imaged by a scanner.
Mushroom identification demands attention to detail. You need to capture the top and bottom of caps, and the stem structure. Sometimes the buried part of the fruiting body is important, or a cross-section, or even the color of a bruise. Sometimes it is necessary to take caps home, place them on a sheet of paper, and let them dry so they drop their spores. The color or even the microscopic shape of the spores helps with IDs. All of which means that you are disturbing the mushrooms you are encountering. I have seen mushroom hunters leave depressing trails of carelessly kicked apart mushroom mounds. Take only what you need for ID (or for dinner, if you are an experienced forager).
Lichens have a clever protective layer that blocks excess light when there is too much or when it is too dry, to protect delicate photosynthetic machinery inside. In this state their colors are muted. During or after rains, this layer turns transparent, and lichen colors are more pronounced. Lichens are also more easily found in late winter or early spring, when there is less vegetation of other kinds. Mosses are also at their best after rains; they dessicate and fade during dry spells.
Scanners. Flatbed scanners are suitable for only a few types of plant photos. The problem is that scanners have very narrow depth of field, so the plant must be squished up against the glass to image well. This so badly distorts many plants that the result is disappointing at best. Scanning works for some grasses, a few small plants, some mosses, flowers too tiny to photograph by macro, and many seeds. Choose a contrasting background. I used a plastic backing sheet from a spiral bound notebook.
Summary. You can take surprisingly good macro shots with a point-and-shoot camera. You can take great ones with an ILC, a macro lens, and the built-in flash. Start by shooting with flash in manual mode at ƒ/22 for closeups. For normal shots, like bushes or trees, shooting in automatic mode is as good a place to start as any—this is a separate topic for another day. If you want the best possible results, add a ring flash.