Lighting For Macro
Apart from focusing, another significant challenge with macro photography is that it can be hard to see what you are doing. Lighting, too, can be a pain.
The depth of field for macro is inherently shallow. As such, you'll probably be shooting most close-up images with the lens cranked down at or near the smallest aperture available to help get as much in focus as possible. And it's hard to get very much light that can get through that tiny opening.
First, let's consider what this means for achieving an acceptable exposure. Obviously, for shooting, you're going to need a stable tripod to avoid camera shake while the shutter is open. But while you may be able to keep your camera from moving this way, your subject may not be so cooperative. Even the slightest breeze can ruin an image when your entire field of view is measured in inches at best. Everything gets magnified, and if anything moves during the shutter, you will probably be able to see it in the result. The obvious answer is to add more light to compensate.
My personal first choice for more light is the use of a reflector disc. These things come in various diameters and cleverly fold up to one-third of their expanded size for transport. By popping one open and positioning it appropriately, you can often bounce some light into the shadows and save the shot. Depending on the situation, this may not be enough, and you'll have to add artificial light.
If you try using a built-in camera flash, or one directly mounted to the camera hot-shoe, you'll probably find yourself with a new problem. Well, perhaps several of them.
Whatever you are shooting won't be very far away from either your lens or your flash. Angle the flash down slightly to fully illuminate your subject, and your lens could end up casting a shadow on the lower half. Not every lens and flash will result in this issue, but many will. By using a flash bracket to relocate the flash head forward or higher up, you can avoid the shadow. Or for flexibility, handhold the flash. Either way, you'll need an appropriate linkage to synchronize the flash output with the shutter release. You'll need a cable to connect the flash and hot shoe electronically, or an IR or radiofrequency system to bridge the gap. The exact solution depends on your camera and flash, but don't wait until you're out in the field to work out the details.
Another potential problem has to do with coverage. Known as the "inverse square law," light levels decrease based on the square of the distance as it spreads to cover a wider area. So regardless of how much light falls on your subject, your background will receive less. Let's suppose that what you are shooting is one foot away, and the background two. Being twice as far away, only one-quarter of the output reaching your subject will hit the background. By definition, an exposure "stop" is a halving or doubling of brightness, so this decrease in background lighting equates to two full stops of exposure loss.
If you've ever wondered why so many macro shots have black backgrounds, this is why. Such concerns aren't apparent in everyday life where the sun is the primary source of illumination. A foot or two one way or the other is irrelevant, given that the sun is 93 million miles away from every subject and terrestrial background. Of course, it's not possible to hold your camera flash at that distance, and it wouldn't be bright enough to do much good even if you could. But by remoting the flash as far off as possible, you can minimize the influence of the inverse square law.
If you have the time and gear available, you could consider employing more than one flash or light source. Such setups used to require a lot of math to calculate light levels for each flash, but modern TTL ("through the Lens") metering simplifies things. You'll have to spend some time upfront learning how all this fancy flash gear works, but once you do, the added flexibility could be just what you need to save the shot. If you're looking for an easy way to get into working with more than one light, consider starting with one light and a reflector. Ease your way in.
But there's a second way in which lighting for macro can be challenging. Using an extension tube, macro lens, or even a longer focal length, you'll lose light through extension. I said earlier that light from your camera flash falls off with the square of the distance. So, too, does the light entering the front element of your lens on its way to the camera sensor. Loss through extension is the reason why long telephoto lenses have such big front elements, while shorter lenses with the same maximum aperture can be smaller. When you add an extension tube on the back of that lens, you'll lose even more. Teleconverters will cost you light, too, by focusing in on just the central ring of light that first entered your lens. High magnification inherently makes for dark viewfinders. Start with an f/4 lens and add a 2x teleconverter, and you'll be down to a maximum of f/8. That's too dark to autofocus in most cases, and it's dark enough to make manual focusing challenging as well.
One option is to add a light source that remains on while you compose. Flashes and strobes fire only briefly when the shutter fires. Simply by shining a flashlight on your subject, though, and you can brighten things up long enough to see what you're doing before you press the shutter release. If you're planning to use a reflector disc, you've got a head start, assuming the light you are reflecting off it comes from the sun or another stable source.
Long ago, I bought a halogen work lamp from the hardware store for use with indoor macro. It put out a great deal of light, but also a lot of heat. I guess I had to sweat for my art. Halogen light has an oddly green color cast, but that was easy to compensate for via white balance. These days, you can do the same thing with a compact LCD light panel. Cool in more ways than one.
You find that you can see better by composing on Live View. Many newer cameras change the display in real-time as you adjust the ISO. Even if you choose not to shoot at a ridiculously high ISO, there's nothing that says you can't temporarily boost things to get set up, then set the ISO to something more reasonable to shoot. Oh, the wonders of modern technology.