SHUTTER SPEED
Shutter speed is a photography term that indicates the length of time the shutter is open to allow light exposure to the film or image sensor. Used in conjunction with aperture size (f-stops), shutter speed determines total exposure and can be changed to create different effects. Shutter speed is measured in seconds, typically fractions of seconds.
Shutter speed is adjusted automatically when a camera is being used in automatic mode. However, shutter speed can be adjusted manually on most SLR film and digital cameras. Conditions that typically account for determining shutter speed include lighting and movement. A slower shutter speed is used in low lighting, while a short, or quick, shutter speed is typically used to capture moving objects. To create dramatic effects, such as intentional blurring or other artistic effects, the shutter speed may be adjusted to atypical speeds for the given conditions.
The shutter speed of most cameras can be adjusted in increments from 1 second to 1/1000 of a second, but longer and shorter exposure times can be achieved on some cameras. There are some rules of thumb for setting shutter speed, such as slower settings in low light and quicker settings for fast-moving subjects, but determining shutter speed for the desired effects is more a matter of trial and error.
To adjust shutter speed, you must first set your camera to a manual setting. Most cameras today will have a digital display viewable on the screen in the viewfinder. Most displays omit the 1 and display only the denominator of the fraction. For example, a shutter speed of 1/125 will be displayed as 125, while 1/500 will be displayed as 500 on screen. A setting of 125 is slower than a setting of 500.
While adjusting the shutter speed in various conditions and for various subjects will change the overall effect of the image, experimenting with apertures and sensitivity (ISO) along with shutter speed settings is essential to understanding the full impact specific settings can have on the overall photograph.
APERTURE
Aperture is one of those words that scares a lot of people. It's something that a lot of us know is there but don't want to deal with. After all, that's why we bought an automatic camera. But aperture is something that every photographer should be aware of, amateur or not. It is one of the cameras functions that set out limitations for every photo we take.
The aperture in a camera is a function of the lens. It works the same way that the iris of our eye works. If you haven't already experienced this phenomenon in science class then grab a flash light and go to a mirror. First turn out all the lights and wait for a few seconds. Turn the lights back on and look into the mirror. Your pupils should be wide open. Now, quickly, shine the flashlight right into your eyes. The pupils will close up pretty quick. This is because your eye is monitoring how much light it lets in, taking only what it needs.
This is the exact primary function of a lens's aperture. An automatic camera will have a light sensor that measures how much light is entering the lens. In a situation where there is a lot of light it will close the aperture to a finer point because it doesn't want to over expose the picture. For photos taken in doors or even at night, the aperture will be opened up.
This function of the aperture works hand in hand with the camera's shutter. Imagine that the camera has an option to keep the shutter open-thereby exposing the film or CCD to light-for anywhere from a hundredth of a second to an entire second. That means the shutter can open and close really fast or really slowly. If too much light enters the camera during any one of these scenarios the picture would be exposed too much. Now let's get back to the aperture. If the camera's aperture is opened wide then a lot of light can get in and the shutter won't have to be open as long. Conversely, if the aperture is closed to a fine point then not as much light gets in and the shutter will have to be open longer.
Before the days of automatic exposures a photographer had to do a bit of math to determine the best way to balance these things. These days the camera does most of the work for you. But it isn't always right! Why? Because the aperture also affects the focus.
Imagine a billion rays of light racing into a lens. The narrower the opening, the more focused those rays will become. In practical terms this means if you took a picture of a person with a wide open aperture then the person may be in focus, but everything in front of them and behind them may be blurry. The more the aperture is closed, the finer the light entering the camera becomes and, in turn, more things get focused. All of a sudden the person is sharp as is the fence behind them and the tree, etc.
The aperture, therefore, acts as both a technical means of taking a photo and a way of adjusting the pictures aesthetics.
Note as well that in photography numbers known as F-stops represents the aperture. The higher the F-stop is, the more the aperture is closed.
ISO SENSITIVITY
ISO is the number indicating a digital camera sensors sensitivity to light. The higher the sensitivity, the less light is needed to make an exposure.
Digital cameras automatically select the ISO but most have a setting to change it manually. Auto ISO generally works best for bright scenes.
Shooting at a lower ISO number requires more light than shooting at a higher number. Lower numbers result in images with the least visible noise, which is desirable. The higher the number, the more noise.
The amount and degree of noise varies from camera to camera. Noise, when present, can be seen throughout a photo but usually appears most in dark areas.
Digital single lens reflex cameras produce images with the lowest noise at all ISO numbers compared to compact cameras. This is because they have larger sensors. However, some consumer digital cameras do better than others when it comes to noise.
ISO SETTINGS
AUTO ISO - digital camera automatically sets the ISO speed according the the brightness of the scene, increasing or decreasing the sensitivity. User has no control over which ISO number is used.
ISO 80 - for taking photos in bright light; excellent for close-ups, landscape, and portraits. Produces fine detail and image quality.
ISO 100 - for extra sensitivity with little, if any, reduced image quality.
ISO 200 - cloudy and overcast days. Acceptable image quality, with some visible noise.
ISO 400 - suitable for indoor photography whether or not a flash is used. Useful for "stop-action" and sports photographs. Most compact digital cameras produce high to very high image noise.
ISO 800, 1600 and above - useful for taking photos in very low light, or outside in good light when increased shutter speeds are required. Results can be disappointing when shooting at these high numbers with compact digital cameras, so take test photos before photographing an important event.
High Auto ISO mode - the camera uses automatically chooses a very high ISO number. If the camera has a High ISO mode, it is usually a fixed number, such as ISO 3200. The camera may also automatically reduce the size of images shot in High ISO mode.