Aperture and depth of field

A couple weeks ago Pat and I purchased a new lens: it's a Canon 85mm f/1.8. I thought this would be a good opportunity to talk about aperture and depth of field.

The simplest way to explain aperture: it's the opening in the lens that lets in light, like your pupil. Therefore, the larger the opening the more light that is let in; otherwise known as a wide aperture. Thus, a small opening is a narrow aperture. Easy enough, right?

Now this is where it can get confusing. A wide aperture = smaller f-stop number setting on your camera. A little counter intuitive. In the case of our new lens: f/1.8 is a wide aperture.

(On a side note: a wider aperture will also increase your shutter speed because it lets in more light; therefore, reducing the potential for camera shake, especially in low light situations).

A lens with a wide aperture is great for portrait photography. It allows you to blur the background making your subject standout; this is an example of depth of field.

Depth of field is how much of the picture is in focus. Thus with a f stop of f/8.0, more of the picture will be in focus then lets say a picture taken at f/2.8 (shallow depth of field). Changing your aperture settings is one way to control depth of field. Other ways are to use zoom or to change the distance between you and your subject.

I find the best way to explain aperture and depth of field is by showing you! So here we go :)

The camera settings I used are below each picture. I shot in aperture priority mode for all pictures.

The first three pictures were taken with our Canon 17-55mm f/2.8 lens:

1/25s,  f/8.0, ISO 100, 55mm

1/250s, f/2.8, ISO100, 54mm

The first picture was taken with a narrow aperture, f/8.0. Notice how more of the background is in focus when compared to the second, taken at an aperture of f/2.8. In the second picture the aperture is wider, thus making a more attractive portrait because the background is less distracting.

1/200s, f/2.8, ISO 100, 17mm

 The third picture is a pull back of our shot location. Not that pretty, right? But by zooming in and choosing a wide aperture you would never know it was a parking lot.

The next two pictures are an example of how to achieve depth of field using zoom. They are taken with our Canon 55-250mm f/4.0-5.6 lens.

1/40s, f/4.0, ISO 100, 55mm

1/100s, f/5.6, ISO 100, 250mm

While standing in the same spot, I took the first picture by zooming out as far as I could with this lens (55mm); in the second picture I zoomed in all the way (250mm). The farther I zoom in, the more the background is out of focus. The second picture is much more appealing to the eye. Note: the farther away the subject stands from the object behind him, in this case the wall, the more the background becomes out of focus.

Another interesting tidbit is that at 250mm the widest aperture allowable with this lens is f/5.6; however, although the aperture is not as wide as the first lens (which is f/2.8), I was able to achieve a blurred background by zooming in.

Finally, the next two pictures were taken with our new lens, Canon 85mm f/1.8. Saving the best for last!

1/30s, f/8.0, ISO 100, 85mm

1/640, f/1.8, ISO 100, 85mm

The first picture was taken with an aperture of f/8.0; therefore, more of the background is in focus compared to the second picture, which was taken with a wider aperture of f/1.8. The effect of a wider aperture allows the subject to POP. The background is smooth and less distracting, allowing the viewer to better focus on the subject.

The last picture is by far the most appealing of the group and the best example of a shallow depth of field. Here is a side by side comparison of the best shots from each group in the order of appearance:

        54mm f/2.8                                                       250mm f/5.6                                                      85mm f/1.8

You will also notice that the field of view is the same for all three pictures. However, the distance between me and the subject changed for each lens. For the first picture (lens: 17-55mm) I was standing less than 10ft away from Pat. The second shot was taken standing approximately 30ft away (lens: 55-250mm). Finally, the third picture was taken at a distance somewhere between the first two shots. It's also worth noting that these three pictures were also taken at the widest aperture available for each lens at their given focal length.

Hope you found this helpful!!

Now a picture of pat in the sun just for fun: