If this series is focused on macro and close-up photography, why do I keep writing about flashes?
A reasonable question. Here’s what I’m thinking:
My camera’s sensor is noisy. Not just a little. When I use an ISO greater than 80, I start seeing levels of noise that make the image objectionable to me. I realize that not everyone is as much of a stickler as I am.
As the magnification of a lens goes up, the depth-of-field (DOF) that is in focus goes down. This can be offset somewhat by closing down your camera’s aperture, which brings back some DOF. But there’s a price: with a smaller aperture, less light gets through the lens and onto your camera’s sensor. So a flash is often helpful to bring some light back into the scene, while still allowing you to shoot with a lower, less noisy ISO.
Once you’ve decided that using a flash is worthwhile, learning to use it off-camera is a great investment into your photos.