F-Stop is NOT an f-word
What exactly is an f-stop anyway?
The term f-stop is sometimes confusing due to its multiple meanings. In photographic terms it can mean the size of a lens aperture or an EV (Exposure value) of light.
Lens aperture -corresponds to the aperture opening of the lens. The smaller the number the bigger the aperture opening. An f/2.8 has a bigger opening then f/8. When you open up a lens by one stop you allows twice as much light into the camera.
The list below shows a typical progression of f-stops. For those techies out there it corresponds to the sequence of the powers of the square root of 2.
f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32
EV (Exposure value) – represents a doubling or a halving of the light exposure either by stopping up or down of the lens aperture or by changing the shutter speed.
By speeding up or slowing down the shutter speed you effectively increase or decrease the amount of light that will enter the camera.
The shutter speed times are actually a fraction of a second. A speed of 1/125 (or simply 125th) really means 125th of a second.