Mechanics
What is depth of field? A technique used to make the photographer’s main subject stand out. This technique blurs the background and keeps the main subject in focus. In the photo above it shows how the focus point is clear and everything else is blurred.
Why should a photographer use depth of field? By using depth of field a photographer can guide the viewers eye and incress intrest by making their focus point stand out.
When should a photographer use a small depth of field versus a long depth of field? You should use a deep depth of field when you want the whole scene to be in focus. You will use a short depth of field when you want your subject to stand out more and the background to be blurred.
In these photos, you can see that as I changed the aperture, the background became more in focus. In the first photo, the brick is blurred, but in the last photo, you can clearly see the brick background.
In these pictures, you can see the differences in aperture. In some of them, you can clearly see the leaves but not the field behind them, and in others, you can see both clearly, and in the other ones, the leaves are blurred and the background is clear.