Here I will cover the basics of depth of field and background photo blur. It’s something that can take a while to get your head around. I may do a more in depth explanation or a video at some point.
Depth of field refers to a part of the image which remains sharp while the remainder is out of focus (blurred out). You use selective focus to make parts of a photo stand out by changing the aperture and increasing your image’s depth of field.
Your camera will only focus its lens at a single point when taking a photo. I’ve used some of my cars to help give you a visual aide to support my explanation.
In the below sample my red Viper is the “depth of field” because it is sharp compared to the background cars, which are both nicely blurred out.
It always looks and feels different depending on your type of camera, aperture and focusing distance. There are generally two fields of view:
Shallow (where only a narrow zone appears sharp)
Deep (where more of the picture appears sharp)
Below is a set of photos shot at different apertures; it should help give you an idea of how the f-number affects the depth of field in the photo.