In the olden days of film and much simpler cameras, it was easy to know when you were increasing or decreasing the shutter speed and/or aperture by one ‘stop’ because this was done by twisting a dial or knob that was labelled by full stops and often had detents at each stop as well - so a ‘stop’ usually really was a stop. ;-)
However, with digital cameras that only have a numeric readout it's not so obvious when one is changing exposure by a full stop or not.
So, if you ever wanted to know what's a full, half, or third stop, below is a chart for you. Click on it for a more readable size.
The scale used for f stop settings starts with 1 (focal length = diameter of the lens opening).
Further illuminating reading on this and related topics, such as EV, can be found at these links...
