Depth of Field is used to focus on a specific something in a picture. depth of field is changed by changing the aperture on the camera, the aperture is a thing that can close and open on the camera lense to let in more or less light, the larger the aperture the shallower the your depth of field meaning less will be in focus, the opposite can be said with a smaller aperture. Depending on your situation you’ll need different depth of fields, if it’s a photo of a landscape then a sharp depth of field is better but if it’s a busy street or just in general has a busy back round then a shallow depth of field is better. The camera angle is also important for depth of field, for example if there’s nothing in the back round then you wouldn’t even be able to tell the difference between a shallow or sharp depth of field.

Wide, or large, apertures correspond with small f/ numbers, such as f/2.8 and f/4. Narrow, or small, apertures correspond with high f-numbers such as f/16 or f/22. wide apertures let in more light than narrow ones, they’re useful when you’re photographing in low light, you want to let as much light in as possible, as you might struggle to get a fast enough shutter speed to get a sharp image. You might also want to use a wider aperture when you want to isolate specific subjects from their backgrounds. A portrait photographer, for example, would typically use a wide aperture of f/1.8 or f/2 so that all the focus can be placed on their subject at the expense of details in the background. while a landscape photographer may use a much smaller aperture such as f/13 or f/16 so that everything in the frame is in focus, from the foreground right through to the background.