F-stops, also known as f-numbers, are a measure of the light-gathering ability of an optical system such as a camera lens. The f-stop is calculated by dividing the systems focal length by the diameter of the entrance pupil. The f-stop is a key factor in determining the depth of field, diffraction, and exposure of a photograph. The aperture controls the amount of light that enters the camera lens, and it’s measured in f-stops. The f-stop number refers to the width of the aperture opening, and it is expressed as a ratio of the focal length to the diameter of the aperture.

Here are some key points to understand about f-stops:

• F-stops control the size of the opening in the lens, which regulates the amount of light that can pass through the lens at a given shutter speed.
• A small aperture (high f-stop number) lets in less light than a larger one (low f-stop number), so it would take longer for the same quantity of light to pass through to the sensor.
• Each f-stop represents a halving or doubling of the amount of light that enters the camera.
• The aperture setting is traditionally adjusted in discrete steps, known as f-stops, and each stop is marked with its corresponding f-number, which represents a halving of the light intensity from the previous stop.
• The f-number is dimensionless and is usually expressed using a lower-case hooked f with the format f/N, where N is the f-number.
• The aperture setting is one of the three fundamental components that make up the exposure triangle in photography, along with shutter speed and ISO.
• The f-stop not only helps you get a proper exposure, but it also helps establish the look and feel of your photo by determining the depth of field.
• F-stops are also used to quantify ratios of light or exposure, with each added stop meaning a factor of two, and each subtracted stop meaning a factor of one-half.
• On modern cameras, f-number is often divided more finely than steps of one stop, with steps of one-third stop (1⁄3 EV) being the most common.

In summary, f-stops are a measure of the light-gathering ability of an optical system, and they control the size of the opening in the lens, which regulates the amount of light that can pass through the lens at a given shutter speed. The f-stop is a key factor in determining the depth of field, diffraction, and exposure of a photograph.