Know your limits
The exposure settings you use will also be dictated by what you’re happy to accept in terms of blur, noise and so on…
■ If you do this for a living, you soon learn what results you can accept in terms of motion blur, depth of field and noise – and what you can’t. Even if you don’t, it’s worth deciding what you’re able to live with for the three settings. But (and this is where auto-exposure and auto-ISO fail to deliver), there are variables, even within each setting. Here are five crucial questions, the answers to which it’s worth working out before you go out shooting:
How slow can you shoot hand-held?
It depends on how steady you are, which is something you can work on to improve, but also on the focal length of the lens. It’s easier to hold steady with a wide-angle lens than with a telephoto, because the telephoto magnifies everything, including your twitches. 1/30 sec with a standard focal length of 50mm should be reliably sharp. In addition, Nikon’s vibration reduction system in some lenses will give you perhaps a two-step improvement, so that’d be 1/8 sec in the case of a 50mm lens – but of course that will only address camera shake, not subject movement.
What shutter speed freezes what movement?
There are so many variables here, from how fast something is actually moving to how fast it’s moving across the frame (this depends on the focal length, its distance from you, and on whether it is moving towards you or crossing in front of you). You need to get used to thinking in terms of speed across the frame.
What aperture gives just-reasonable depth of field?
Take a regular subject in a regular crop, such as two people talking a few metres from the camera and framed with a standard lens so that they fill a third or half of the frame. How much needs to be sharply focused and how much can be blurred? An aperture of f/5.6 is a usually a good starting point.
How much depth from the smallest aperture?
When you’re aiming for deep focus, it’s more usual to think of it the other way round. Knowing that you want full depth of field, it’s usual practice to start with your lens stopped down, to f/16 or f/22, and then find the camera position that allows front-to-back sharpness. Knowing roughly what this will be from experience saves time.
How much noise can you tolerate?
Even here there are variables, because noise is at its most visible on very smooth mid- and mid-to-dark-toned areas. If it’s a detailed scene, you will be able to tolerate more noise than if you’re shooting a clear sky, smooth skin or a blank wall. And if you display the image small, that too will hide the noise.
1/30 sec at f/2, ISO1250 I wanted to use selective focusing here. An aperture of f/2 ensured sharp focus on the statue. I knew from experience that at 1/30 sec I’m safe from camera shake. That left just the ISO for adjustment.