Depth of field is one of those photography terms that professionals use all the time but what does it actually mean?
The depth of field is the distance in front and behind your subject that appears in focus. For example, if you take a photo of a flower with a short depth of field the foreground and background will be blurred eliminating surrounding distractions while just focusing on the single flower subject. Increasing the f-stop or f-number creates a smaller aperture (hole for the lens) which also creates a larger depth of field. Wow that was a mouth full and more than my brain could actually wrap around, here it is again very simplified… larger f-stop number equals larger depth of field and conversely a smaller f-stop number equals a smaller depth of field.
Do I expect for you to run right out and start playing with depth of field and f-stops? No, most of us use the automatic settings on our cameras for the majority of our photos. Understanding why your photos look the way they do will help you take better photos. There will be those occasions when you will want to have more control over your settings to produce a specific photographic result. To change your camera f-stop you will have to take your camera out of the automatic mode and know how manually change the f-stop settings.
Typically portraits should have a small or short depth of field. When taking portraits of people focus on their eyes. Their eyes need to be the sharpest part of their face in focus. Then the surroundings start to fade away very quickly. Landscapes should have a longer depth of field so the foreground and far distances are all in focus. Like a photo of a rolling hillside should be in focus throughout the entire depth of the photo.
There are several complicated formulas that actually determine depth of field. My high school algebra teacher told me one day I would need to use those algebraic formulas but photography is supposed to be fun not work. If you really need to determine depth of field there are a few depth of field calculators on the internet. They take your specific camera, lens, f-stop and subject distance into consideration giving you a depth of field distances. I personally say throw out the formulas and use your brain to find your creative side.