This is actually a very good question and it’s one I hear a lot. Budding photographers want to know if, after setting a specific aperture size, they can preview the depth of field that will appear in the photograph they take. Even if a specific aperture setting isn’t made and the camera is in another priority mode, auto mode or full manual mode, it’s nice to know what you’re in store for regarding the depth of field. As it stands, when you meter the camera and view the scene through the viewfinder or rear Live View screen, the camera is giving a preview with the aperture wide open, regardless of what the actual setting is. As you can imagine, this isn’t ideal and having a way to preview where the blur will be and where the sharp areas will be is helpful.
The answer is, yes, you can preview depth of field and it’s actually a very simple process. If you take a look at the side of my Canon Rebel T6i DSLR camera, you’ll see a button that sits directly below the lens removal button. Take a look.
If you press this one button at any time and view the scene through either the viewfinder or the Live View screen, you’ll see exactly what the depth of field will look like. Let me warn you though, things may get dark when using that preview button. Since we can’t preview shutter speed, the camera can’t take a longer exposure into account when showing the depth of field preview. So, the result is a darker view. Just a warning. This is a great feature to have available though, especially when using a larger aperture size that let’s lots of light through. You’ll get a glimpse of all that wonderful and creative blur you’re after.