When you start out with macro photography, there are two problems that can easily get annoying.
The first problem is getting a decent depth of field. The more your lens magnifies a subject, the more narrow the depth of field will be. That means you want to shoot at the smallest aperture you can.
The other problem is motion blur. Both the camera and the subject might move. Because you are photographing small subjects, even very small movements will blur the picture noticeably. That means you will want the shortest shutter times you can get.
The combination of small aperture and short shutter time, means you need a lot of light. The easy answer to getting a lot of light is flash.
Using a flash adds its own set of problems. You can see where this is going: The chief cause of problems is solutions! However, we aren't looking for perfect solutions. If we did, we'd spiral down into solution hell. Rather, we are looking for problems we can live with.
What are the problems with flash? The ones we have to deal with. There are two. The first is that we need to direct the light to where it does some good. As long as we are shooting hand held, the easiest way to do that, is to take the flash off the camera, and hold it in your hand. You can use a cable, or a remote controller. I use a remote controller. It's handy for many things besides macro photography.
The second problem is that when we add flash, we suddenly have to deal with two, very different types of light sources. A flash unit provides a strong, very short pulse of light. We also have ambient light, the light we normally have all around us.
When we take a picture using flash, we will get two different exposures from those two sources. The flash pulse is very short, maybe 1/5000s, or even shorter. This means, if the flash was the only light source, the resulting image will have no perceptible motion blur. We might not freeze a speeding bullet with an ordinary flash, but we can eliminate camera shake and stop the motion of an insect. No problem.
Ambient light is another matter. The ambient light will not be strong enough to give us the short exposure time and small aperture we want. On the other hand, it may be strong enough to cause a blurry image. Not good.
If the ambient light is mostly a source of problems, what if we can get rid of it? We know the ambient light will affect the exposure as long as the shutter is open. We also know the wider the aperture (the smaller the f-number), the more ambient light we will get.
Thus, if we use a short exposure time, and a small aperture, we'll get rid of as much of the ambient light as possible. We can't use shorter times than the flash sync can handle, which usually is 1/250s. Small aperture means high f-number, so we'd like to shoot around f18 to f22. Great news, because this gives us the wide depth of field we also want.
Yay!
By now you should not be surprised if I tell you I shot the fly above at 1/250s, f18, ISO 100. I used a Tamron 60mm 2.0 macro lens and a Canon 60D. The flash pulse is so short it is not affected at all by the shutter time, but a lot of the ambient light is cut. This eliminates camera shake and motion blur.
Bumblebee at at 1/250s, f22, ISO 200. This is the only one of the pictures taken with the flash mounted on the camera. This means I had to work at a slightly greater distance from the subject. Afterwards, I cropped the picture a bit tighter than I usually do.
Fly at at 1/250s, f18, ISO 200.
I should mention that you will need to do some post processing, because straight out of the camera, pictures like these often look rather dark. I usually crop the pictures, increase exposure, edge sharpen, increase definition, and sometimes increase saturation. I often add a bit of vignetting to darken the corners.
Ants at at 1/250s, f18, ISO 100.
All of these pictures were taken the same day, during two walks. And, all of the pictures were taken in flower beds. All you need is a DSLR with a macro lens, a flash, and a cable or remote control unit.
Best of all, I had fun doing it!
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