First Stop, F stops!
The little slideshow above goes through the basics of F stops, we will go into a bit more detail here.
The F Stop is the way you control the Aperture of your lens. Aperture is the more technical way of talking about it, but all the terminology is the opposite of the way you refer to F Stops, so it gets a bit confusing! We will from here on forward only use the word F Stop.
The F Stop refers to how big the opening of your lens is, and therefor how much light is let in and how much of the scene is in focus - i.e. the Depth of Field
F Stops are the main creative control you have when using a camera. The amount of blur or focus a photo has is the main technical thing that has an artistic influence on the look of the photo.
When you use a low F Stop (1.2-2.8) the depth of field is very small so you get lots of blur in the background and foreground, and only what you are focusing on will be sharp. Low F Stops let lots of light into the camera.
A medium F Stop (3.5-4) will give you a medium depth of field, still with some blur in the foreground and background. Medium F Stops let a medium amount of light into the camera.
A high F Stop (5.6+) will give you a large depth of field, with most of the scene in focus at 5.6, and more and more in focus the higher the number gets. High F Stops let less light into the camera.
To explain how depth of field and focal planes work, we like to think of it from a birds eye view. Try to imagine these slides as little scenes we are shooting straight in towards, with the guy in black shooting with a camera in the first scene, and a camera just out of frame shooting in towards the cake scene.
The focal plane describes the amount of the scene parallel to the camera lens that will be in focus.
The closer you are to a scene, the smaller the area the same focal plane covers, that is why you can get so much more of that pretty blurry background stuff when you are shooting a close up scene than you can when you are shooting something from further away.
Hopefully this will help you to see why you can’t get more than one person in focus when you are shooting at a low F Stop unless they are in the exact same focal plane. This is why we always photograph people around 3.5-4 and big groups at around 5.6
We know this sounds confusing at first, so read over this page a few times to try and get your head around it. Hopefully it will all start to click into place the more you read it!