How can you control photographic exposure? You have three ways - adjust the shutter speed, the aperture or the light sensitivity. With film photography, you have just two degrees of freedom within the camera settings: aperture and shutter speed. The third variable, sensitivity, is a characteristic of the film, not the camera. (The light sensitivity of film is rated as an ISO number, with higher numbers indicating more light sensitivity.) Once you've made your choice to use film of a given sensitivity - say ISO 100 - this variable is locked down until you change to a different film. There are workarounds, such as push processing, but the results aren't always satisfactory.
One of the characteristics distinguishing the digital image sensor from film is its variable sensitivity to light. Thus, with digital photography, sensitivity becomes a camera controllable variable, alongside aperture and shutter speed. This means that when you shoot digital, you have a third degree of freedom to play with in deciding the best exposure.
This won’t matter much to you if you always set your camera to Auto, but it might explain why more of your pictures are keepers since you started shooting digital. On Auto, the camera will pick the best combination of exposure variables to ensure the best possible picture. With a film camera, that means setting the best shutter speed and aperture combination. Often though, the limitation is the film speed – you have slow daylight film in the camera but you want to take some indoor shots, for example. Since the film camera has no way of altering film speed, it does the best it can, but the results are often photos that are underexposed because the camera was pushed beyond the limits of its maximum aperture setting or blurred because the shutter speed it picked was set too slow for hand-held shots. The third degree of freedom available to a digital camera means that the camera can also boost ISO sensitivity, so a proper exposure can be calculated under more lighting conditions – dark or light.
If you are an advanced shooter, you probably know about the aperture-priority and shutter-priority settings on your camera, and when it’s most appropriate to choose one or the other. If you want to control depth of field, aperture priority is the mode to use, since you dial in the aperture setting to match the depth of focus you want to achieve, and the camera calculates the proper shutter speed for a correct exposure. Likewise, if you are shooting fast moving subjects, you’d pick shutter priority, which lets you choose a specific shutter speed – say 1/1000 sec. - with the camera calculating the correct aperture setting for a proper exposure. Both of these scenarios can be enhanced now that you can also vary the ISO setting - shot by shot if need be.
Landscape photographers often want a photograph that’s razor sharp from foreground grass to distant horizon, and thus choose very small aperture settings to maximize depth of field. Nature photographers using extreme telephoto lenses will choose small aperture settings for a similar reason – to maximize depth of field (which tends to be quite shallow at high telephoto settings). Because less light comes through the lens set to a small aperture, the shutter has to be open longer to make the proper exposure, and of course that creates camera steadiness problems. Using a tripod might be a solution for landscape photographers, but might not be so workable for nature photographers who have moving subjects like birds or roving animals. By setting the digital camera to a higher ISO, you can have your small aperture and a faster shutter speed.
With shutter-priority, the same benefits exist. Say you are shooting your daughter’s volleyball game, and in order to stop the action, you need to use a fast shutter speed. If the gymnasium lighting isn’t bright enough, you may have to use a wide open aperture, which means the focusing will be very shallow. Boost the ISO, and you can stop down the aperture, to keep more of the action in focus, and still use a fast shutter speed.
High ISO used to be synonymous with increased digital noise, and while that can still be an issue, camera makers have made great progress in either taming the noise, or making it look less objectionable, more like the visible film grain of high ISO film stocks. It’s a variable worth exploring.
One of the characteristics distinguishing the digital image sensor from film is its variable sensitivity to light. Thus, with digital photography, sensitivity becomes a camera controllable variable, alongside aperture and shutter speed. This means that when you shoot digital, you have a third degree of freedom to play with in deciding the best exposure.
This won’t matter much to you if you always set your camera to Auto, but it might explain why more of your pictures are keepers since you started shooting digital. On Auto, the camera will pick the best combination of exposure variables to ensure the best possible picture. With a film camera, that means setting the best shutter speed and aperture combination. Often though, the limitation is the film speed – you have slow daylight film in the camera but you want to take some indoor shots, for example. Since the film camera has no way of altering film speed, it does the best it can, but the results are often photos that are underexposed because the camera was pushed beyond the limits of its maximum aperture setting or blurred because the shutter speed it picked was set too slow for hand-held shots. The third degree of freedom available to a digital camera means that the camera can also boost ISO sensitivity, so a proper exposure can be calculated under more lighting conditions – dark or light.
If you are an advanced shooter, you probably know about the aperture-priority and shutter-priority settings on your camera, and when it’s most appropriate to choose one or the other. If you want to control depth of field, aperture priority is the mode to use, since you dial in the aperture setting to match the depth of focus you want to achieve, and the camera calculates the proper shutter speed for a correct exposure. Likewise, if you are shooting fast moving subjects, you’d pick shutter priority, which lets you choose a specific shutter speed – say 1/1000 sec. - with the camera calculating the correct aperture setting for a proper exposure. Both of these scenarios can be enhanced now that you can also vary the ISO setting - shot by shot if need be.
Landscape photographers often want a photograph that’s razor sharp from foreground grass to distant horizon, and thus choose very small aperture settings to maximize depth of field. Nature photographers using extreme telephoto lenses will choose small aperture settings for a similar reason – to maximize depth of field (which tends to be quite shallow at high telephoto settings). Because less light comes through the lens set to a small aperture, the shutter has to be open longer to make the proper exposure, and of course that creates camera steadiness problems. Using a tripod might be a solution for landscape photographers, but might not be so workable for nature photographers who have moving subjects like birds or roving animals. By setting the digital camera to a higher ISO, you can have your small aperture and a faster shutter speed.
With shutter-priority, the same benefits exist. Say you are shooting your daughter’s volleyball game, and in order to stop the action, you need to use a fast shutter speed. If the gymnasium lighting isn’t bright enough, you may have to use a wide open aperture, which means the focusing will be very shallow. Boost the ISO, and you can stop down the aperture, to keep more of the action in focus, and still use a fast shutter speed.
High ISO used to be synonymous with increased digital noise, and while that can still be an issue, camera makers have made great progress in either taming the noise, or making it look less objectionable, more like the visible film grain of high ISO film stocks. It’s a variable worth exploring.
Atom Feed (xml)
No comments:
Post a Comment