Moving Beyond Automatic Mode

Transcription

1 Moving Beyond Automatic Mode When most people start digital photography, they almost always leave the camera on Automatic Mode This makes all the decisions for them and they believe this will give the best chance of capturing the image. They are also concerned that if they tried one of the other modes, it would mess up what could otherwise be a good photo. Almost all Point & Shoot cameras, and many DSLRs have different automated Scene Modes (Portrait, Landscape, Macro, Sunset, Sports, etc.) that give you a little more control and maybe a little more ability to be creative, within some fairly safe boundaries. Exposure Triangle Aperture, Shutter speed, and ISO. These elements share a reciprocal or interdependent relationship when you change one, it has an effect on the other/s. Aperture a HOLE through which light is admitted. Shutter speed controls HOW LONG THE LIGHT IS ADMITTED ISO is a measure of the SENSITIVITY of the sensor or film to light Page 1 of 6

2 1. Aperture. Moving Beyond Automatic Mode Aperture controls HOW MUCH LIGHT IS ADMITTED. In photography, this is usually measured in f/stops, represented by a number. Contrary to what you might imagine, the smaller the f/ number, the bigger the opening or aperture. e.g. An aperture of f/2.8 is wider open than an aperture of f/11. The wider the opening or aperture, the more light hits the film or sensor. The more light that hits the film or sensor, the less time is required for a correct exposure. The more light that gets in, the faster your shutter speed can be When you open or close a lens aperture, you double of halve the area that allows light to enter. This in turn doubles or halves the exposure. For example f/8 allows twice as much light as f/11 and f/5.6 will allow twice as much again and so on. f/11 f/8 Aperture can also have an effect on Depth of Field (or DOF). DOF is the area of sharpness in the image. In landscape photography there is usually a deep DOF, with everything in focus, from foreground elements, mid ground elements, and background elements. In portrait photography, a shallow DOF is often used, with only the eyes in sharp focus, and everything in front of and behind the eyes slightly out of focus. More on Depth of field later! Page 2 of 6

3 2. Shutter Speed The shutter on the camera allows light to enter and strike the film/sensor. Shutter speed controls HOW LONG THE LIGHT IS ADMITTED. Faster shutter speeds stop action, slower shutter speeds blur action. It is the length of time a shutter is open; the total exposure is proportional to the duration of light reaching the sensor. There are three factors that affect the shutter speed: the scene luminance, the ISO sensitivity and the aperture size. You can trade off shutter speed and aperture by using units of stops. A stop up and down on each will halve or double the amount of light regulated by each. For any given total exposure, or exposure value, a fast shutter speed requires a larger aperture (smaller f number). Similarly, a slow shutter speed, a longer length of time, can be compensated by a smaller aperture (larger f number). Shutter speed is measured in seconds. Shutter speed can also effect the sharpness of your pictures due to camera shake. The longer the focal length, the more pronounced camera shake will be. In general, the longer the focal length (300mm is a longer focal length than 50mm, for instance), the more camera shake will blur images (and not in a good way). The general rule of thumb is to set a shutter speed that is at least the reciprocal of the focal length. If you have a 50mm lens, use of shutter speed of at least 1/50th second. For a focal length of 300mm, choose a shutter speed of at least 1/300 second. Page 3 of 6

4 3. ISO ISO is a measure of the sensitivity of the sensor or film to light. The lower the ISO (100, for example), the less sensitive the film or sensor is to light (and longer the exposure time is). The higher the ISO is (1600, for example), the more sensitive the sensor or film is (and shorter the exposure time is). A digital camera has the ISO rating to indicate the level of sensitivity to light. The normal setting is ISO 100. The most common ISO settings are ISO 200, ISO 400, ISO 800 and ISO 1600 or even ISO 3200 on some DSLRs. ISO sensitivity works pretty much the way a microphone and amplifier does. If you try to record with a microphone and your voice is loud and clear, you won't need too much amplification to obtain a good recording; but if your voice is extremely thin, you'll have to crank up the volume to register it. Obviously other sounds will be amplified as well, and there will be audible noise The same goes for digital cameras. The sensor must use a higher sensitivity under low light conditions. The price is image noise. Top end cameras are usually good performers in the image noise department, but any compact and ultra compact camera will have a very bad performance with high ISO sensitivities and even at low ISO numbers in shade areas there will be luminance noise. ISO effect the Image Quality (IQ). Lower ISO generally offers much better IQ, while higher ISO usually leads to more digital noise and image degradation. Fortunately, many new cameras have much improved high ISO performance. Understanding these elements and their relationship to the other gives us more creative control of our photography and helps our images turn out they way WE want them too, rather than how the camera thinks they should turn out. Page 4 of 6

5 The Sunny 16 Rule An approximately correct exposure will be obtained on a sunny day using ISO 100, an aperture of f/16 and a shutter speed of 1/100th of a second. This is called the sunny 16 rule: at an aperture of f/16 on a sunny day, a suitable shutter speed will be one over the sensor sensitivity. Exposure Compensation When you use the Manual mode you are in command of the exposure. In semi automatic modes P, Av and Tv you choose only some of the parameters and the camera sets everything else. In such cases you can still have control of the exposure using the Exposure Compensation control if you have one. The A or Av (Aperture Priority) mode There is a mode that allows the photographer to set the aperture and then expose the photograph automatically. This mode is called "Av" (aperture priority) and it is useful when you want to control the depth of field or the amount of light entering the sensor. Using the Av mode in a macro photograph of a flower, you may decide to set the aperture at f/11 to have a wider depth of field; you would choose a value of f/11 and the camera will set the ISO sensitivity and shutter speed to expose the photo. Even if you don't like the setting of the camera, you can adjust the exposure to over expose or under expose the photograph to your taste. In the same case, if you want only a small part of the flower focused and everything else blurred you should use the maximum aperture (e.g. f/2.8). That will have two benefits: enhanced Bokeh and faster shutter speed that would be really useful if you are hand holding the camera. Page 5 of 6

6 The S or Tv (Shutter Priority) Mode The photographer chooses the Shutter speed and the camera adjusts the other settings to keep the exposure correct. You ll probably use this mode the most when making decisions about moving subjects. If you re taking shots of birds in flight, a higher shutter speed allows you to freeze the action, requiring a shutter speed of, say, 1/1000 sec for slower moving birds (geese), or 1/2000 sec or higher for really fast subjects. High Shutter Speed Low Shutter Speed On the other hand, if you want to blur the action a little, as in a shot of a stream or waterfall, you ll want to slow down the Shutter speed a bit, from maybe 1/2 sec to even several seconds. If you re shooting hand held rather than using a tripod, remember to keep the shutter speed at a reciprocal of the focal length (1/50sec for a 50mm lens, for instance). The higher the shutter speed, the less chance of camera shake. The P (Program) Mode This is actually an automatic mode of the camera. The camera takes all the guess work (and control and creativity) from the photographer and makes all the decisions, and adjusts aperture, shutter speed and ISO automatically. Many photographers leave their camera set on Program mode and never look back. The benefit of Program mode over full AUTOMATIC mode is that you can override some of the settings that you can t in AUTOMATIC mode. If your camera has a dial on the top of the front grip, you can quickly change aperture or shutter speed, and the camera will compensate the other settings to keep exposure correct. Page 6 of 6