This is a shallow DOF shot that I took of a friend's son testing for his black belt. I shot it with an 85mm f/1.2 lens at f/2. If I had to do it again with the same equipment, I would have shot at f/2.8 or maybe even f/4 instead. I'm very happy with how it came out, but this was the "Big Moment" in the test and shooting that wide was risky. The picture is better for it, but with such shallow DOF I took too much risk that I would miss focus and end up without a good shot. With my new camera, I trust the eye detecting autofocus a lot more.

Canon 5D Mark III, 85mm, f/2, 1/400, ISO 1600.
It is much easier getting shallow DOF with a telephoto lens than it is with a wide angle lens. Shooting at f/2.8 with a relatively near subject and a 200mm lens will give you shallow DOF. Shooting at f/2.8 with a wide angle lens won't unless you are very close to your subject. That makes it hard to shoot wide and use DOF to isolate your subject. Here is an example shot where I got close to my subject (which makes it easier to blur the background) and shot with my aperture wide open.

Canon 7D, 24mm, f/1.4, 1/100s, ISO 400
And another at a sweet sixteen party. I wanted to show the two girls and the setting they were in, but the background was very distracting, so I wanted it blurred.

Canon 5D Mark III, 24mm, f/1.4, 1/160s, ISO 3200
You would think that taking a picture with a super small aperture, like f/32 would mean that EVERYTHING is in focus. Not so. Remember that your DOF gets smaller the closer you are to your subject. This is a macro shot taken very close but with a very narrow aperture. Even though I shot with a narrow aperture, the front and back of the little car are out of focus. The best way to deal with this is to take a bunch of pictures focusing on a slightly different part of your subject with each picture. You combine all of them using a program that does what is called "focus stacking". That takes the sharpest parts of each picture and combines them so that you get more stuff in focus. When you see pictures of tiny things like bugs, that is often what they are doing.

Canon 5D Mark II, 100mm, f/32, 8s, ISO 200
Here's an example of a landscape with a lot of DOF. Generally speaking, you want to avoid using apertures above about f/11 because, while they give you more DOF, the small aperture hurts the sharpness of your image. It's a tradeoff. If you really want the best possible landscape with lots of DOF, use the focus stacking technique by taking several pictures and combining them.

Canon 1D Mark II, 38mm, f/18, 1/30s, ISO 200
There is a fun trick that you can do with a camera with a wide aperture lens. It works best with a prime lens rather than a zoom because you really want the aperture to open wide. You cut out a shape and cover the lens with it. That forces the incoming light to go through your cutout shape. The out of focus stuff in the background takes on that shape. It works best with lights in the background. Here are some of our Christmas lights shot through a Mickey cutout I made with a 4"x4" piece of wood and a laser cutter. I mounted the cutout into a Lee filter holder on the front of my lens.

Canon R5, 200mm, f/2.8, 1/200s, ISO 6400 And just in case it wasn't clear, those are ordinary Christmas lights shot through a Mickey Mouse shaped cutout.