Cameras and Photography
	Sir John Herschel, a 19th century astronomer and one of the first photographers, came up with the term 'photography' in 1839. The term is a combination of two Greek words -- 'photos' meaning light and 'graphein' meaning writing (or drawing). The term 'camer'a comes from camera obscura, Latin for 'dark room.' A traditional camera obscura was a dark room with light shining through a lens or tiny hole in the wall. Light passed through the hole, forming an upside-down real image on the opposite wall. Analogue Cameras A still film camera is made of three basic elements: an optical element (the lens), a chemical element (the film) and a mechanical element (the camera body itself). The only trick to photography is calibrating and combining these elements in such a way that they record a crisp, recognizable image. The Lens At its simplest, a lens is just a curved piece of glass or plastic. Its job is to take the beams of light bouncing off of an object and redirect them so they come together to form a real image. Film The chemical component in a traditional camera is film. A chemical record of the pattern of light by using a collection of tiny light-sensitive grains, spread out in a chemical suspension on a strip of plastic. When exposed to light, the grains undergo a chemical reaction. Once the roll is finished, the film is developed -- it is exposed to other chemicals, which react with the light-sensitive grains. In black and white film, the developer chemicals darken the grains that were exposed to light. This produces a negative, where lighter areas appear darker and darker areas appear lighter, which is then converted into a positive image in printing. Color film has three different layers of light-sensitive materials, which respond, in turn, to red, green and blue. When the film is developed, these layers are exposed to chemicals that dye the layers of film. When you overlay the color information from all three layers, you get a full-color negative. Body The components which allow you to control the access of light through the lens to the film. 2 Major factors; How much light is passing through the lens How long the film is exposed 1. Aperture To increase or decrease the amount of light passing through the lens, you have to change the size of the aperture -- the lens opening. This is the job of the iris diaphragm, a series of overlapping metal plates that can fold in on each other or expand out. Essentially, this mechanism works the same way as the iris in your eye -- it opens or closes in a circle, to shrink or expand the diameter of the lens. When the lens is smaller, it captures less light, and when it is larger, it captures more light. 2. Shutter speed Standard camera SLR 35mm -- optically corrects view through viewfinder using mirrors Digital Cameras The key difference between a digital camera and a film-based camera is that the digital camera has no film. Instead, it has a sensor that converts light into electrical charges. All the fun and interesting features of digital cameras come as a direct result of this shift from recording an image on film to recording the image in digital form. Sensor Technology There are two different sensors used on cameras today: CCD sensors - CCD sensors have been around longer. In general, CCDs have more pixels and work better in low light. However, they tend to be more expensive and they use a lot of power. CMOS sensors - CMOS sensors are lower resolution, use less power and do not work well in low light. If you are looking for an inexpensive, low-resolution camera, and plan to use it outdoors, a CMOS sensor would be a good choice. High-resolution cameras need a CCD sensor. Lens You will find four different types of lenses on digital cameras: Fixed-focus, fixed-zoom lenses - These are the kinds of lenses you find on disposable and inexpensive film cameras -- inexpensive and great for snapshots, but fairly limited. Optical-zoom lenses with automatic focus - similar to the lens on a video camcorder, you have "wide" and "telephoto" options and automatic focus. The camera may or may not let you switch to manual focus. Digital-zoom lenses - With digital zoom, the camera takes pixels from the center of the image sensor and "interpolates" them to make a full-size image. Depending on the resolution of the image and the sensor, this approach may create a grainy or fuzzy image. It turns out that you can do the same thing a digital zoom is doing on your own -- simply snap a picture and then cut out the center of the image in your image processing software. Replaceable lens systems - If you are familiar with high-end 35 mm cameras, then you are familiar with the concept of replaceable lenses. High-end digital cameras can use this same system, and in fact can use lenses from 35 mm cameras in some cases. Focal Length 35mm Equivalent View Typical Uses 5.4 mm 35 mm Things look smaller and farther away. Wide-angle shots, landscapes, large buildings, groups of people 7.7 mm 50 mm Things look about the same distance as what your eye sees. "Normal" shots of people and objects 16.2 mm 105 mm Things are magnified and appear closer. Telephoto shots, close-ups Optical Zoom vs. Digital Zoom In general terms, a zoom lens is any lens that has an adjustable focal length. Zoom doesn't always mean a close up. As you can see in the chart above, the "normal" view of the world for this particular camera is 7.7 mm. You can zoom out for a wide-angle view of the world, or you can zoom in for a closer view of the world. Digital cameras may have an optical zoom, a digital zoom, or both. An optical zoom actually changes the focal length of your lens. As a result, the image is magnified by the lens (sometimes called the optics, hence optical zoom). With greater magnification, the light is spread across the entire CCD sensor and all o f the pixels can be used. You can think of an optical zoom as a true zoom that will improve the quality of your pictures. A digital zoom is a computer trick that magnifies a portion of the information that hits the sensor. Let's say that you are shooting a picture with a 2X digital zoom. The camera will use half of the pixels at the center of the CCD sensor and ignore all the other pixels. Then it will use interpolation techniques to add detail to the photo. Although it may look like you are shooting a picture with twice the magnification, you can get the same results by shooting the photo without a zoom and blowing up the picture using your computer software. Resolution The amount of detail that the camera can capture is called the resolution, and it is measured in pixels. In general, the more pixels your camera has, the more detail it can capture. The more detail you have, the more you can blow up a picture before it becomes "grainy," and starts to look out-of-focus. Some typical resolutions that you find in digital cameras today include: 256x256 pixels - You find this resolution on cheap cameras, like those you would buy for a child. This resolution is so low that the picture quality is almost always unacceptable. This is 65,000 total pixels. 640x480 pixels - This is the low end on most "real" cameras. This resolution is great if you plan to e-mail most of your pictures to friends or post them on a Web site. This is 307,000 total pixels. 1216x912 pixels - If you are planning to print your images, and want them to look nice, this is a good resolution. This is a "megapixel" image size -- 1,109,000 total pixels. 1600x1200 pixels - This is "high resolution." Images taken with this resolution can be printed in larger sizes, like 8 inches x 10 inches, with good results. This is almost 2 million total pixels. You can find cameras today with up to 3 million pixels.
	Also see: How Cameras Work by Tom Harris How Digital Cameras Work by Karim Nice and Gerald Jay Gurevich
shiralee saul 2002	photography index >>