Basic explanation of depth of field and f-stop
Depth of field explained
You have probably heard the term depth of field (DOP) being thrown around by other photographers. What is depth of field and what can it do for your photography? Depth of field is basically the distance between the nearest and furthest objects in a frame that is acceptably sharp. You would have no doubt noticed in photographs where the models face is pin sharp, but the background is completely out of focus. That is depth of field.
There are a few factors that affect DOP; the lens focal length, distance from camera to subject, f-stop, these all effect depth of field. I'm going to focus (excuse the pun!) in on f-stop, as it is this setting that affects the visual effect of DOP the most.
If you shoot on aperture priority on your camera, you have control of how much you open or close your aperture, which determines how much light reaches your sensor (or film back in the day). The amount your aperture is opened or closed, is determined by the f-stop or f-number. Depending on your lens it can be anywhere from 1.4 - 22. The lower the f-stop value you select the wider or more open your aperture is, therefore allowing more light on the camera's sensor. This is ideal for low light photography or where light is scarce. The higher the f-stop value, the smaller your aperture opening will be, allowing less light on your sensor. This is obviously great when it is very bright, and you don't want your image to be over exposed or blown out.
What happens to the depth of field when the value of the f-stop changes? Lets assume we shooting on aperture priority, just to make this easier to understand. When you shoot on aperture priority, you select the f-stop value, and the camera will do the math for us and automatically choose the appropriate shutter speed. If we shoot at an f-stop value of 1.8, our shutter speed will be very fast and our image will have a very narrow depth of field, meaning that only a small percentage of our photograph will be sharp and the rest will be out of focus. When we shoot at higher f-stop values, you will notice that more of the photograph will be in focus. This is great for landscape photography, when you want as much of the landscape as sharp as possible.
Depth of field can be used in creative ways in your photography. Try playing around with different settings and see what differences you can spot. Once you understand the concept you will be able to apply it to your photography and it will become second nature. Good luck and enjoy!