Back to the beginning of A Short Course in Macro Photography

Illumination   Magnification   Focus

Macro Illumination

If you've spent time shooting bug macros, you've discovered the near-necessity of flash illumination as your primary light source, especially as your reproduction size approaches 1:1 or greater. There are several reasons why flash may be the most practical option:

The use of a small aperture--likely f11, f16 (or beyond) if shooting near life-size** subjects
Macro lenses lose light as focus is racked to maximum reproduction size
You're (likely) shooting a fast-moving subject
You may be using extension tubes that dramatically reduce the amount of light striking the image plane

So What's Up with this Lifesize Stuff?
**"lifesize" refers to the 1:1 ratio comparing size of the image striking the image sensor (or film plane) and the size of the subject, itself.
In other words, you achieve lifesize if shooting a subject that is the same size physically as the width it occupies on the image sensor. For example, if the subject happens to be the same size as the image sensor, upon viewing or print-out, the subject spans the entire length of the displayed image file on your screen or printed image without any cropping, regardless of screen size or enlargement size.

The Challenge of Available Light versus Flash

Simply, there is just barely enough light on our sweet planet to get the job done if you need a small aperture and high magnification.

For example: Even on a sunny summer day, you end up cranking up the ISO just to get f11 at a workable shutter speed when shooting macro. Here's a shot at f10 at ISO500 at 1/640. For this shot, I had the camera on a tripod and awaited some activity:

Available light butterfly and bee

So again: bright sun on a July day--so the sun's high in the sky--and with a macro lens as you turn the focus toward minimum distance, less light strikes the image sensor. As a result, one of your exposure variables gets compromised, likely it's a combination of aperture and ISO. That's how this shot ended up being shot at ISO 500. That relatively high ISO begins to compromise the quality of your image, both in terms of image noise and color fidelity. Bear in mind that this shot isn't even really macro and I was hitting the wall. Imagine the challenge of using an extension tube and wanting f16. You'd almost need zero wind and a dead bug. When you use flash for macro, suddenly your exposure options are no longer limited. Any aperture, any ISO, and the shutter speed, although now limited by your camera’s flash synchronization, is no longer a concern because the flash will likely freeze all motion, almost regardless of subject motion, even at a pokey 1/250th.

So flash seems to be all good, or is it?

Next: So what's wrong with flash?