Close-up: Lighting for Macro
Small apertures and high magnification leads to dark viewfinders and long shutter speeds. No doubt about it, shooting macro brings with it a need to concern yourself with lighting. I've mentioned previously the benefits of having a good solid tripod so you can keep your camera still during while the shutter is open, but it's worth spending some time considering your lighting options as well. For a natural look, your best bet is natural light. Even if your subject doesn't move around though, you can improve your images by modifying the light nature provides.
A diffuser is a large metal hoop covered in translucent nylon. Folding it up is probably worth a PhotoTip in its own right, but I'll differ that for another day. To correctly use one, hold it as close as possible to your subject (but outside the frame). Used this way it will diffuse the light passing through it to create softer shadows and more even illumination. Held further away, it merely casts a shadow on your subject which is generally not what you want.
A reflector is constructed the same way as a diffuser but is covered with either solid white or silver/gold material instead of translucent cloth. This allows you to reflect additional light on your subject by aiming it like a mirror. The white side generally will look more natural but regardless of which side you prefer, it can often be best to start with the metallic side to simplify the aiming process. If you have a reflector with a gold or soft gold finish you can use it to add some warmth to your subject. Be careful not to overdo it though. One useful technique is to aim it in such a way that the light form it barely glances off the subject rather than shining directly on it. Hold it in such a way that the light it is casting is pointed parallel to the plane of the subject and just touches it rather than being pointed perpendicular to it.
With both diffusers and reflectors you will be thankful your camera is on a tripod so you have your hands free to modify the lighting.
I only ocasionally use flash for outdoor macro. The light from a flash (or any source for that matter) decreases the further it travels and spreads. Quantitatively, the decrease is inversely proportional to the square of the distance it travels. For example, if you hold a flash two feet from your subject (remember that macro working distances are short) and the background is another two feet behind that (a total of four feet from the flash), the background will be twice as far away as the subject is (four feet is twice two feet). This will make the light falling on the background be only one fourth that which falls on the subject (one over the square of the ratio of the distances). As you probably know, a stop in photography is the halving or doubling of one of the variables affecting exposure. So, if the light on the background is only one fourth that on the subject, then it is two stops darker (one half would be one stop, and one quarter is two stops). Since we really only have five total stops to deal with for the most part, and if we expose our subject as medium toned, you can see that the background will be pretty much falling into shadow.
Rarely in daylight will your subject be properly exposed but the background be black or nearly so. This is because the sun is a lot farther away that a flash would be so the ratio of distances problem pretty much disappears. You can learn from this and hold the flash further away yourself. If, instead of only two feet, the flash were four feet from the subject and the background still two feet beyond that (for a total of six feet now), the background would only be half again as far away (six divided by four) instead of twice as far. Again squaring this we find that the light on the background would now be one over 2.25 that on the subject, or just less than half (about one stop instead of two). Nikon makes the SC-17 cord to allow you to take the flash off camera and other manufactures make similar cables. Wireless flash extenders are also becoming more popular. Nikon released the SU-4 some while back and newer flashes such as the SB-800 feather built-in wireless flash capability.
You may be familiar with ring lights, flash heads that feature bulbs on both sides of, or completely surrounding the camera lens. For coins and stamps, using one can help create even illumination over the subject. For nature work though, the light ends up looking equally flat and even creating a situation that doesn't look, well, ... natural. I've never been a fan of ring flashes and don't own one.
For indoor shooting a great solution is to use a halogen shop light. I bought one at a large local hardware store with two 500-watt bulbs for less than $50. It certainly generates a lot of heat, but it puts out a lot of light as well. I can set it up some distance from the subject and it will still put out plenty of light to shoot by. Since the light is continuous, the viewfinder image will be a lot brighter than without so it also makes focusing easier too. On film, you may need to worry about the proper filtration to compensate for the color of the light (probably a bit on the green side), but with digital it is easy to pre-white balance and ignore the whole issue.
Next week, we'll look at options for macro flash brackets.