One thing that regularly comes up in the training courses and 1-2-1 sessions I run is what is the point of aperture?
Other than composition and lighting, it’s our main creative control. Why? Because it acts as a means of isolating objects from a background (or making them all sharp and not isolated). Let’s just stick with the isolating bit for now. It’s the control that blurs stuff out. If I focused on one of the pears in the examples below and an aperture of F32, everything would be in focus – the whole scene. At F4 or “wide open” (depending on your lens) I can pick a smaller piece of the scene out and blur the rest.
Note – the wider you shoot and the further away you from something, the less obvious this blurring or isolating effect is. It is when you’re close that it has the impact.