Photography Basics

I have a point and shoot Canon s100 camera with handful of manual functions. Mostly I take pictures in the "auto" setting but I wanted to learn the basics so that in case of moving objects or dim-lit areas, I can take nice pictures. Below are few notes from my experimentation.

It seems to me that exposure determines the quality of a photo. Exposure is a combination of aperture, shutter speed and light sensitivity of the sensor (ISO setting). A picture is great if it has the right combination of these 3 key components. Let's take a look at them one by one.
Aperture determines depth. It controls the opening (cone angle) through which light enters. Narrow aperture means more parallel light enters the cone resulting in sharp focus. Wide aperture means less parallel light is admitted resulting in sharp focus only on what the lens is focusing on. Rest of the image is little blurry. Apertures are specified as f-number or f-stops for ex. f/2.0, f/2.8 etc. Lower number means wider aperture. Below are few pictures in  apertures f/2.0, f/4.0 and f/8.0.



Shutter Speed
Shutter speed is the time for which the shutter is open. This controls the amount of light reaching the camera. Its usually denoted as 1/200s, 1/500s etc. Exposure with a shutter speed of 1/250s and f/8 is the same as with 1/500s and f/5.6 however the picture would be different. Below are few pictures with varying shutter speeds.






ISO Speed
ISO setting controls how sensitive the camera sensor is to the light that reaches it. Higher ISO setting means more sensitivity. Higher setting allows you to take photos in darker conditions without flash but it also creates more noise reducing the image quality. The values are measured as 100, 200, 400 etc. ISO200 is twice as sensitive as ISO100 and 4 times less sensitive than ISO800. Every time the ISO setting is doubled, the exposure is halved. It is generally recommended to keep the ISO setting to its lowest and manipulate the shutter speed and aperture. Below are few pictures in varying ISO speeds.