Advantages of SLR Photography
For people who have mastered using an SLR in manual mode, the opportunities for better technical shots and creative approaches to difficult lighting situations offer a big advantage not found in other cameras. Better control of aperture and shutter speed gives SLR users an unrivaled flexibility and adaptability in challenging shooting circumstances. The better lenses available, plus the ability to swap out lenses as shooting conditions change, give the 35mm SLR user a distinct edge over those shooting with less sophisticated equipment.
Another feature of automatic SLR cameras is preset shooting programs or program modes. The most fully automatic of them, often referred to as full program mode, selects the aperture and shutter speed, switches on the camera's built-in flash unit if necessary, and focuses the lens. All you have to do is snap the shutter.
Other common automatic program modes include the following:
When not in fully automatic mode, SLR cameras offer two different methods for setting exposure. Aperture priority allows the user to set the aperture, after which the camera automatically sets the appropriate shutter speed. This priority setting allows you to control depth of field.
Shutter priority lets you choose the shutter speed you'd like to use, and the camera takes care of the aperture. This priority setting is good for times when you want greater control over how action scenes are shot, such as using a fast shutter speed for stopping action or a slower speed for blurring it.
Another feature on many SLRs is exposure compensation control. This allows complete control over the camera's autoexposure system and makes it possible to set the camera to over- or underexpose your image by up to two or three stops in either direction. Exposure compensation is good for working in backlit situations to shed more light on foreground subjects, or for other times when you want to use a different exposure than the camera's metering system suggests.
This technology, which was introduced in the 1980s, helps eliminate blurry images and is probably the most popular feature on SLR cameras. There are two types of autofocus systems: active and passive.
Passive autofocus uses the light rays that pass through the lens to measure the contrast and adjust the focus until it's as sharp as it can be. The more focus points a camera has, the faster and more easily it will focus.
Active autofocus systems work by sending a beam of infrared light from an emitter on the camera body. A sensor then measures the distance from camera to subject according to the length of time it takes for the infrared light to bounce back from the subject. Active autofocus works in the dark and can handle pictures with few high-contrast areas to focus on, but it can also be fooled by objects closer to the camera and by reflective surfaces like window glass. Most SLRs have passive autofocus capability, which you need to handle the variety of lenses that go on the camera.
SLR autoexposure systems measure the brightness of the scene and then set the shutter speed and the aperture accordingly for the correct exposure. Some systems use a sensor on the front of the camera. Most SLRs, how-ever, use through-the-lens metering, which is more precise and increases the accuracy of the exposure. TTL metering systems use several methods to measure light:
Center-weighted metering takes a reading from the center of the viewfinder.
Matrix or evaluative metering divides the picture area into a grid and then analyzes the contrast and brightness in each part of the grid to come up with a suggested exposure.
Spot metering takes a reading from a small circular area in the viewfinder and then sets the exposure for the entire picture based on this reading.
The specific metering system varies depending on the camera model. Center weighting is the most common, with matrix metering and spot metering usually available on more expensive models. Some cameras offer all three, allowing the photographer to choose the metering method that best suits the situation. Spot metering, for example, is great for scenes with lots of contrast, as it allows you to take a series of readings from specific areas of a picture and then decide which readings you want to use for the effect you're trying to achieve.
Also called a motor drive, this mechanism automatically moves the film through the camera each time the shutter is clicked. On many automatic film SLRs, it can be set to allow you to fire the shutter once every time you push the shutter release button, or continuously for several frames — as long as you don't run out of film — while you hold the shutter release button down. Digital SLRs have basically the same feature, a “burst” mode that allows you to capture multiple pictures with one firing of the shutter release button.
These are common features in automatic film SLR cameras. Drop in the cassette, pull the film leader across to the correct spot (if necessary), close the back, and the film advances to the first frame. Most systems also set the film speed automatically to make sure it's exposed correctly.
Auto rewind is activated when the roll is complete and the camera senses that it can't pull any more film out of the cassette. The camera then automatically activates a motor that rewinds the film. Film can also be rewound before all the frames are exposed by pressing a film rewind button.
