In order to understand what F stop is, let me tell you that even though working on auto mode gives you the simplicity to take photos in a breeze when you switch it to manual you have so much more control. In manual mode you are able to choose the settings for the aperture, shutter speed, and ISO. Out of the 3, aperture is probably the most important one to capture a great photo.
You might be asking what is aperture? It’s the hole in the center of your lens in which light passes through. Aperture is one of the 2 components that make up the exposure, the shutter speed is the other one.
When the aperture is larger there is more light that comes in causing the image to be brighter and the smaller it is the darker the image is.
Another important effect that aperture brings is depth of field — the amount of your photo that appears to be sharp from front to back. For example, the two photos below have different depths of field at different apertures.
So what is F stop? The “f” stands for “focal length.” When you substitute focal length into the fraction, you’re solving for the diameter of the aperture blades in your lens. (Or, more accurately, the diameter that the blades appear to be when you look through the front of the lens.)
For example, say that you have an 18-50mm lens zoomed to 50mm. If your f-stop is set to f/10, the diameter of the aperture blades in your lens will look exactly 50mm/10 = five millimeters across.
This is a cool concept. It also makes it easy to visualize why an aperture of f/2 would be larger than an aperture of f/10. Physically, at f/2, your aperture blades are open much wider.