When you talk about photography, we basically have 3 controls : Aperture, Shutter Speed and ISO speed.
Before we get into technical jargon.. let's understand Aperture, Shutter Speeed and ISO in simple terms..
Let's take look at the functioning of your Eye.. When you are in bright sunlight, eye lids come closer to reduce the amount of light that can go inside.. When you are inside dark movie theater, eye lids wide open.. This is behavior is nothing but controlling Aperture based on the need..
Let's say, you are looking directly at bright sun in the afternoon.. you would not able view the sun directly for longer.. if you do, you go blurred... so you look at sun for a while and then close your eye... so it's Shutter Speed that determine when to close your eye...
Now comes the ISO Speed.. Human's eye cannot see properly in the night but Cat can see in night.. Then we can say that Cat's ISO Speed (or Sensitivity) is more than Human's ISO Speed (or Sensitivity)..
Let's talk about camera functioning now..
Camera is box with a lens at one end and light sensitive film or digital sensor at the other end. A lens will have a diaphragm that opens and closes to allow the light to pass through. The amount of light which can be passed through lens is called "aperture".
When the light crosses this diaphragm, the shutter exposes this light to a digital film for consistent amount of time; the amount of time is determined by "shutter speed".
'ISO speed' determines the sensitivity of the digital sensor. The higher the ISO speed the faster the camera collects light but it also adds more noise to the photograph than the lower speeds. Increasing ISO speed is nothing but increasing processing speed of digital sensor.
More about each of these controls now... Let's also discuss about purpose of each of this control.
1. Aperture:
Aperture size is usually measured in f-numbers or f-stops. The smaller the f-stop number, the larger the lens opening; the larger the f-stop, the smaller the lens opening. The aperture (f-stop) determines the amount of area which is in camera's focus.
The f-stop is a fraction that indicates the diameter of the aperture. The f stands for the focal length of the lens, the slash (/) means divided by, and the number represents the stop in use. For example, if you were shooting with a 100mm lens and with an an aperture of f/2, the diameter of the actual lens opening would be 50mm. Here, 50 (focal length of the lens) divided by 2 (stop) equals 50 (diameter of lens opening). So smaller the f-stop number, the larger the lens opening; the larger the f-stop, the smaller the lens opening. An aperture of f/1.4 will have very very focus, while f/32 is extremely narrow focus. If the aperture is set to large value, the surroundings which are not in camera's focus get blurred. Aperture can be used to draw attention to one subject (like the flower on the right) by blurring the background with a wide aperture (low f/stop). Aperture can also be used to focus everything in a picture with a narrow aperture (high f/stop).
Adjustment to the aperture controls the depth of field, the distance range over which objects are acceptably sharp; such adjustments generally need to be compensated by changes in the shutter speed.
2. Shutter Speed:
As discussed above, shutter speed determines amount of time the light coming from the lens is allowed to stay on the sensitive film. Shutter speed (more literally exposure time) is measured in seconds, but often marked in reciprocal seconds. A typical exposure time for photographs taken in sunlight is 1/125th of a second, typically marked as 125 on a shutter speed setting dial. Very short shutter speeds are used to freeze fast-moving subjects, for example at sporting events. Short shutter speed for example can be used to freeze subjects in midair with a fast speed or it can be used to blur water with a slow speed i.e., short shutter speed is suitable for capturing water falls with high speed. High shutter speeds are often used in low light conditions, extending the time until the shutter closes, and increasing the amount of light gathered. Very long shutter speeds are used to intentionally blur a moving subject for artistic effect. High shutter speed means lens closes fast.
3. ISO Speed:
The common span of ISO speed is 100 to 800. If you are trying to take pictures in dim light without a tripod, you might want to raise the ISO speed in order to get a picture that's not blurry. Most of the time you should keep it at a lower ISO speed if there is enough light, but it makes a big difference when there isn't. Note that, ISO speed and Shutter Speed are related. When you increase the ISO from 100 to 200, you are cutting down the amount time required to capture the scene on the digital sensor by half. So when you change the ISO from 100 to 200, your shutter speed may change from 1/125s to 1/250s.
What is Depth of Field?
It's the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.
In the following figure, the area within the depth of field appears sharp, while the areas in front of and beyond the depth of field appear blurry.
Let's take a look at another image...
What is Exposure?
Amount of light which needs to be captured on digital sensor is called "
exposure".
Exposure can be treated as a function of Aperture and Shutter speed because both of these can control the amount of light. Various parts in a scene can have different light intensities. For example, if you are wearing a bright white shirt, your shirt has more light intensity than your face. If the exposure is set based on your shirt, your face will look dark. If exposure is set based on your face, your shirt color may washed out. Camera finds best average light intensity for the scene and digital film gets exposed to the light based on this intensity. If the light is too much then the picture will be washed out. If the light is not enough ten then picture will be too dark.
As discussed, exposure is the amount of light collected by digital film. Cameras have light meters which measure the light in the given shot and set an ideal exposure automatically. If you control this, you can get creative picture some times.
Look at the following image to know about the trick of exposure:
http://www.twin-pixels.com/wp-content/uploads/exposure-tutorial-7.jpg
The two values – shutter speed and aperture are intertwined. To get the correct exposure, both have to be set correctly – that is, if you increase the exposure time then you need to decrease the aperture. Exposure can be treated as function of all these.
For the given exposure, a fast shutter speed requires a larger aperture (smaller
f-number). Similarly, a slow shutter speed, a longer length of time, can be compensated by a smaller aperture (larger f-number).
What is 'Rule of Thirds' or '2/3rd Rule'?
In this rule, objects in the snap are given 2/3rd or 1/3rd of the area. Usually, objects are confined to 1/3rd of the area. Instead of having objects like 'crime convicts' in the middle, it's good cover the space in which the object is located. For example: If you are covering birthday cake with candles, confine it to 1/3rd of the space and leave the remaining space blank instead of covering just cake in the middle. If you are covering an ant, confine it to1/3rd of the area, and, use the remaining space to cover the direction in which it's heading.
Applying Rule of Thirds Vertically:
If your snap is covering both water and the sky and if you want to give emphasis to water then it should get 2/3rd portion of the snap. If your snap is covering water, hills and sky then you may want to give 1/3rd portion to each.
Applying Rule of Thirds Horizontally:
If you snap is covering an object (Tree, Person, etc), you may want to keep it in the 'left most' or 'right most' 1/3rd portion of the snap.
Few Tips:
- Capture the non-obvious things. Try different things. [Ex: Capturing just one Eye and blurring other eye, Capturing hands but not faces, etc]
- Create things [Ex: Sprinkling water on flowers, etc]
- Camera Flash is strict NO-NO. It takes-out naturality from the snap. If you really need to use flash (in case of insufficient light), cover it with light paper, etc.
References:
http://www.twin-pixels.com/photography-understand-exposure/
http://photo.net/learn/basic-photo-tips/aperture-shutterspeed-iso/
http://www.picturecorrect.com/photographytips/ExposureBasics.htm
http://photo.net/learn/basic-photo-tips/aperture-shutterspeed-iso/
http://www.betterphoto.com/article.asp?id=135
http://en.wikipedia.org/wiki/Depth_of_field
