Well shooting manual allows you to make the decisions, not your camera. Ever wondered why when you are shooting in a dark room your images are blurry? Because you are letting your camera choose your settings. Are you getting very grainy images in some shots? That’s your camera making decisions for you. Do you want to learn how to shoot stars at night, or light trails from cars streaking down a freeway? Then you have to take back creative control.
So let me see if I can break this down simply for you.
The first thing you need to understand is how a basic camera records light.
There are 3 elements which go in to determining how much light is recorded in any exposure you make:
APERTURE: This relates to the size of the hole which opens up in your lens to let light in. Normally Aperture is denoted as an F-number and describes how wide the lens is opening up to let light in. F22 is a fairly small aperture in your lens and won’t let a lot of light in, where as a good quality lens may open up to F1.2 which will be a very wide aperture and lets a lot of light in.
SHUTTER SPEED: This relates to the length of time which the shutter opens within the body of the camera to expose the film or the sensor to the light coming in through the lens aperture. When you hear that click after pressing the shutter button, that is the sound of your shutter opening and closing to allow light to hit your sensor so it can capture an image. Shutter speed is given in increments of time from 1/8000 of a second being a very fast shutter which doesn’t let a lot of light through, to 30 seconds which would expose the sensor to light for a long period of time.
ISO: This relates to you camera sensor, or your film stock. In the old days of shooting film people understood this well. If you knew you would be shooting on a bright sunny day you would buy less sensitive film, namely 100 speed. If you were going to be shooting in a low light situation you would buy 1600 speed film because it was very sensitive and captured more light coming in. The digital age has kept these numbers and we now talk about setting the sensitivity of our sensor for different lighting situations as our ISO number. The common ISO range is from 100 to 6400 in most modern cameras and the important thing to remember is that the higher your ISO number, the more sensitive your sensor is to light coming in.