Have you ever wondered what many refer to f-stops or f-number...Well I am going to explain how these terms apply to you. All lenses have a variable or constant aperture. A variable aperture for example would be f/3.5-4.5. What that means is that at the lower end of the zoom, it starts at 3.5 and as you zoom in more, it gradually increases until it finally maxes out at 4.5. A constant aperture for example would be f/4. This means that throughout the zoom range, it remains constant at f/4. What do all these numbers mean to you?
First off the the f-stop goes from 1,1.4,2,2.8,4,5.6,8,11,16,22...going from f/1-2 is 1 stop and going from f/1-1.4 is .5 stops
These numbers simply mean how much light the lens can let in. What this means is that f/1 gathers twice as much light as f/2 and three times as much light as f/4.
Most prime lenses (lenses that have a fixed focal length ex: 50mm) have a lower f-stop and therefore can let in much more light. Also since it can not zoom in and out, it has a constant aperture.
Most zoom lenses (lenses that can zoom in and out ex: 18-55mm) have either a constant or variable aperture. Constant aperture zoom lenses are more expensive than variable aperture.
You can always increase your f-stop, but if your lens says f/4, it can't go down to f/2.8..
In a later post, I will give techniques on how to use iso, aperture, and shutter speed to achieve the pictures you want...