PHOTOOG Photography writings by Olivier Giroux

25Sep/080

Photography 101 : Master the half-press

Modern cameras are bristling with buttons, but when it comes down to it there is only one you need to master: the shutter release. How hard can mastering one button be? When this button is the only one that actually does something, it might deserve some attention.

There are two independent computers in your camera. The most obvious one allows you to browse pictures and menus on the rear LCD, but it is more of an accessory to the camera because it doesn’t operate the camera. The main computer coordinates your camera’s critical operations: exposure metering, automatic focus, flash calculations, image capture.

You interact with the main computer by providing decision hints and by triggering its action. Hints are varied and can be as simple as “you decide”, for example when using picture styles or “green” mode. All actions are triggered by partially or fully depressing the shutter release – this distinction is the key to control your camera effectively.

The main computer’s operational tasks are split into two phases. In the first phase it prepares to take a picture by focusing the lens and measuring the luminance of the subject to determine exposure parameters. Then in the second phase, the picture is captured by activating the aperture, mirror and shutter mechanisms.

Many novice users do not perceive these two phases separately because both are triggered immediately when the shutter release is depressed fully and quickly (e.g. by hammering the button). To insert a pause between the two phases, only depress the shutter release partially (you’ll feel a light stop) and then hold it down. This is called the “half-press”, and while it is maintained the computed settings of the main computer are locked-in. Further pressure from a half-press position will execute the second phase and take the picture with these settings.

Why would you want to pause after the first phase? There are several advantages.

First, this gives you a chance to review the computer’s choices before committing them to a picture. The most important choice you should evaluate is focus. Did the camera actually focus on the subject you intend to photograph? If it chose wrong, let go of the shutter release and repeat the half-press, the camera will try again.

Second, you get a chance to re-frame the image with current settings before taking the picture. Most cameras have 5 or 9 focus points you can choose from for off-center compositions, but many debutant photographers are uncomfortable with focus point selection and elect not to use them. Also, seasoned photographers know the center point is typically the most sensitive and accurate under difficult conditions. For simplicity, you may want to always focus with the center point irrespective of the framing you want in your picture – the half-press enables this.

Third, some operations of the camera take time and add delays that get in the way of capturing a fleeting moment. Focusing the lens, for instance, can take a few seconds under some conditions. If you predict a photo-opportunity is imminent, you can pre-focus the lens with a half-press and hold until the moment arrives. Obviously this works best for stationary subjects.

Fourth, when you can predict a photo-opportunity but not exactly where it will occur, use your camera’s continuous-focus option. When continuous-focus is enabled the half-press locks in all settings except focus, which is then re-evaluated at high frequency for as long as you hold the half-press. You must follow your subject’s sideways motion but the camera will track its distance automatically to keep it in focus.

Finally, if you are using a lens with an image-stabilization function (IS or VR) then it too operates continuously while holding the half-press. The VR mechanism needs a second or two to engage fully, during which time it learns how your hand is moving. It benefits greatly from holding the half-press for that amount of time before taking a picture, so it is worth integrating this pause into your shooting habits.

Note that the benefits of the half-press aren’t reserved for DSLR users, most pocket cameras also support it with most of the same benefits.

Your camera is full of features that claim to deliver improved image quality, but the truth is that there is no feature with benefits more compelling than the half-press. Nor are the other features as easy to master as using a single button. At a minimum you should be able to reduce the chance of coming home with blurry pictures of your vacation, and that’s the whole point of using this camera in the first place.

I hope you enjoyed this article, there will be more coming.

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