[...] > What I need, is to find a web site / document / book that can > get me off the ground, > with explaining what ISO/shutter/aperture/exposure/etc.. are, > how how they relate to each other, and affect each other, and > the picture > [...]
Most beginners' photography books should teach you that in a few pages, with some shooting exercises. You also need to learn about exposure metering, in particular the difference between incident and reflected light readings, and their pros and cons. Michael Freeman has been writing such books for many, many years and they seem to work well - try something like his The Complete Guide to Digital Photography. Here's a quick overview. Exposure determines how much light hits the sensor. The ISO number is a measure of how sensitive to light the sensor is. The higher the number, the more sensitive it is. The more sensitive it is, the less light you need to record the correct exposure. The ISO numbers usually double - each doubling represents twice the sensitivity, and a corresponding halving of the amount of light needed to hit the sensor. In bright sunlight you typically use a lower sensitivity than you would in deep shade or at night - it gives you more options for setting your aperture and shutter speed. The amount of light that hits the sensor is determined jointly by the size of the hole which lets light into the camera, and how long you keep the hole open. The size of the hole is set using the aperture and measured in f stops, such as 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 etc. The smaller the number, the larger the hole and the more light you let into the camera. Each number in the series above represents a halving of the area of the hole. So f/1.4 is twice the area of f/2, which is twice the area of f/2.8 etc. (More accurately, the aperture is the hole; the thing that determines the size of the hole is the diaphragm.) How long you keep the hole open is set by the shutter speed, which is normally measured in fractions of a second, but can also be much longer than a second. Usually the speeds run from about 1/30th, 1/60th, ..., 1/4000th of a second. Once again, each step represents a halving of the amount of time the hole is open. The amount of light in a scene is measured with a light meter. Meters built into the camera measure the amount of light reflected from the scene, and make an assumption that the scene reflects 18% of the light falling on it. This assumption provides a reference point, but can fool the meter under certain conditions. The other main type of meter is an incident meter. These are usually hand-held separately from the camera, and measure the amount of light that's falling on the subject. Both types of meter give you the same type of reading. For the meter to work properly you have to set it to the same ISO number as your sensor. The meter reading gives you an exposure value, or EV. You can set various combinations of f-stop and shutter speed on your camera to let in the correct amount of light to match the EV. For example, 1/1000 sec at f/8 lets in the same amount of light as 1/250 at f/16. If you change one without changing the other you are likely to under- or over-expose. Under-exposure means you haven't let in enough light, and the picture looks too dark or muddy; over-exposure means you've let in too much and the picture looks too bright and washed out. A good deal of the creative control in photography lies in how you combine the aperture and shutter speed, and this is where you need to start experimenting to understand the theory. Varying the shutter speed makes moving subjects more or less blurred in the picture. Varying the aperture determines how much is in focus in front of and behind the object you've focused on. So a larger aperture (smaller number) means less is in focus and you can get a nicely blurred background; a smaller aperture (larger number) means more is in focus, and you tend to get a sharper picture. Here endeth the first lesson. It's now playtime. Bob -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
