Collins Complete Photography Course. John Garrett
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Название: Collins Complete Photography Course
Автор: John Garrett
Издательство: HarperCollins
Жанр: Изобразительное искусство, фотография
isbn: 9780007372522
isbn:
Macro lenses are the sharpest you can buy. Most are about 55-60mm focal length, used with film; their focal length is effectively increased by 50 per cent on a digital camera. They are relatively inexpensive and you will probably be able to find a secondhand one at a good price on eBay.
Photographers keep to their favourite lenses over many years. It is often not so much that there is anything particularly special about that lens, but that it suits the way they see the world and the type of work they like to do.
Good-quality lenses, especially those with large apertures, can be very expensive. However, independent lens manufacturers such Sigma and Tamron make high-quality lenses for most DSLRs at about half the price of the camera manufacturers’ lenses.
Focusing modes
Your lens is focused via three modes that are selected from a switch on the camera body: S, C and M.
• S Single auto will automatically focus on the object that you point the camera at when you push the shutter button halfway down. It will fix that focus until you release the button or take a picture.
Reflex telephoto lenses have an internal mirror system and fixed aperture. Their creative characteristic is that they turn out-of-focus highlights into doughnut-like shapes.
A recent addition to some lenses is vibration reduction (VR), which allows you to shoot with lower shutter speeds and still get a sharp image. VR may be incorporated in the camera body instead of the lens.
• C In continuous auto, the camera will follow focus on a moving object when you keep your finger halfway down on the shutter button.
• M In manual mode the camera is focused by using the focusing ring on the lens. The focus indicator dot will light up when you are in focus.
Most DSLRs give you a choice of where to place your point of focus in the viewfinder. This could be a single point that you can move around the viewfinder and place where your subject is. Alternatively, you can group a number of the points together to cover a larger focus area in the viewfinder. This varies with different camera models.
Focusing modes
Focus lock
You will also have a focus lock on the camera. This may be a question of pressing the shutter release button halfway down, or there may be a separate button.
Exposure
The two devices that the camera uses to make an exposure are the aperture and shutter. Working in tandem, they determine the amount of light that creates the image when you release the shutter.
The aperture
A camera lens contains an iris diaphragm, based on the functioning of the iris in an eye. It is constructed of metal leaves that open and close, making a bigger or smaller aperture in the lens through which light enters the camera. The aperture thus controls the volume of light that’s allowed to reach the film or sensor.
The size of the aperture is calculated in f-stops. Confusingly, the smallest number on your lens, such as f/2, is the largest aperture, and the highest number, perhaps f/16, is the smallest. The reason for this is that these numbers are actually fractions, representing the focal length of the lens divided by the diameter measurement of the aperture.
The shutter
Located in the camera just in front of the film or sensor, the shutter controls the length of time that either is exposed to the light entering through the aperture. The main shutter speed settings are in steps, each of which halves or doubles the length of the exposure; for example, 1/250 second allows half the amount of light through the lens as 1/125 second, while 1/60 second allows twice as much.
Modern cameras have a large range of exposure time settings, from 30 full seconds to 1/8000 second. There is also a setting called either B or Bulb, which keeps the shutter open for as long as the shutter release button is held down (you will need a cable release or remote control to keep the shutter open for an extended period). Shutter speeds on the dial are in fractions of a second until they reach 1” second, the symbol “ denoting full seconds.
Your camera has different shooting modes: S (single), which takes a single frame each time you press the shutter release and C (continuous), which is a built-in motor drive that can take up to 6 frames per second (depending on your shutter speed) while the shutter button is held down or until the film is finished or the card is full. This continuous mode can be great to use when you are panning or trying to capture a fast-moving subject. Some cameras offer the option of low and high speed continuous shooting (CL and CH respectively).
Shooting modes
All these aperture and shutter combinations have produced the same exposure for this picture. If either element of the combinations were to be changed the image would be brighter or darker.
1/250 second atf/4
1/125 second at f/5.6
1/60 second at f/8
1/30 second at f/11
1/15 second at f/16
The aperture and shutter function in relationship to each other, because in order to maintain what you or your meter calculate to be accurate exposure, both the volume of light entering through the aperture and the length of time the film or sensor is exposed to that light must be adjusted. If you increase the volume of light by enlarging the aperture, to maintain the same exposure you have to shorten the shutter speed.
Exposure meters
The exposure is calculated by your DSLR or SLR camera’s built-in exposure meter. When you compose a picture in your viewfinder, the meter analyses the light reflected off the subject and calculates what it considers to be СКАЧАТЬ