David Pogue's Digital Photography: The Missing Manual

Use a Manual Mode?

All SLRs, and some fancier compact cameras, offer the mystifying but ultimately rewarding modes labeled P, A, S, and M. They're designed to give you much more manual control over the exposure of each shot than you'd get in a scene mode or auto mode.

You can read much more about these manual modes in the next two chapters. But here's a quick rundown:

• P (program mode). Program mode is a lot like auto, really; the camera chooses the aperture size and shutter speed on its own, ensuring a correctly exposed photo almost every time.

  The difference is that you can override a few of the choices the camera usually makes itself—like white balance, ISO, drive (burst) mode, and, most useful of all, whether or not the flash goes off. If you have an SLR, in particular, you can think of P mode as, "Just like auto, except I get to say when the flash fires." It's terrific.

  Note

  Not to split your head open or anything, but there's also something called program shift mode on some SLRs. Once you've half pressed the shutter button in P mode, the camera displays the shutter speed and aperture that it would like to use—but it permits you to tweak either of those settings; it compensates by adjusting the other setting, exactly as in A or S modes (described next). The steps vary by camera, but it might entail half pressing the shutter button while you turn a control dial.

• S (shutter-priority mode). A famous semiautomatic feature. You adjust the shutter speed, usually by turning a dial (on an SLR) or pressing the arrow buttons (on a compact)—but as you do so, the camera helps you out by adjusting the aperture size (f-stop) to compensate for the change in shutter speed. That way, you don't have to worry that you'll wind up with a crazy exposure. Details on Use Stabilization.

• A (aperture-priority mode). Just the opposite. You adjust the aperture size, and the camera compensates by changing the shutter speed. Details on Where to Find It.

• M (manual mode). For veteran shutterbugs only. In fully manual mode, the camera doesn't compensate for anything. You can change the shutter speed and aperture size completely independently, potentially creating absolutely hideous exposures, and the camera simply sits back and keeps its little mouth shut. It makes no attempt to warn you that at f22 and 1/500th of a second, shot indoors at night without the flash, your photo will look like a slab of onyx in a coal mine at midnight.