Learning about Aperture settings on your lens (Part 2)

In part 2 we are going to focus on a very interesting side-effect of different size apertures.  It is referred to as Depth of Field (DoF.)   In your typical point and shoot style cameras, you didn't worry or even really think about DoF.  Basically, due to the small sensor, you had a very deep depth of field all the time.    Now that you have a DSLR (or ILC) camera with a larger sensor, you have the opportunity to start to control depth of field.

So what is Depth of Field???

It is the plane of focus in your photograph.   If you have a very shallow depth of field, only a small sliver is actually in focus.

In this example with the dominos, you can see that only one of the dominos is in focus.  The second one in line is nice and sharp, but the dominos in front and back of that one are not in focus or blurry.  This is what you would consider a shallow depth of field.   Once again there is a bit of math behind what makes this happen, but we'll keep if fairly simple to start.   A large aperture, in this case f/2.8, creates a shallow DoF.  We will get into more details regarding focal length and sensor size as well as distance to your subject and how they will affect the DoF in a much later post.   

Now, as you can imagine, the opposite is true.... a small aperture will result in a deeper depth of field.

The above picture (far less pleasing, but illustrates DoF) was taken at f/25.   Now all the dominos are in focus.  In fact, even things far behind the dominos are in focus.

The takeaway here is....   Large aperture (small numbers) result in a shallower depth of field whereas smaller apertures (large numbers) result in deeper depth of fields.    Knowing this will really help you construct the photographs you want.

Here is a fun example of using a shallow depth of field for an artistic effect:

My daughter is holding this doll at arms length.  You can see how your eyes are drawn to the in-focus doll, yet you still see my daughter in the background.