Photo Tip Friday - What is the Focal Point and Depth of Field? Part 2

by Mary Denman

Welcome back for Photo Tip Friday! 

Today is Part 2: Understanding Depth of Field. 

Last week, in Part 1, I talked about what the focal point is and how it can change the feel of the picture. You can read about it here.  Once you understand what the focal point is, you then need to learn about depth of field because they go together and can have a great impact on your pictures.

Let's get started learning what depth of field is and how you can control it. 

Depth of field is the amount of the picture that's in focus.  You can think of it as how "deep" the part in focus is in the picture. 

This is determined by the Aperture Value (Av). The Aperture is the size of the opening in your camera that allows light in.  It's an inverse number. (Sorry, but you need the math.) The typical ranges in Aperture Values go from f/1.4 to f/22.

An Aperture setting of f/1.4 lets in a large amount of light because the opening is large. 

Hence, you don't need to have the shutter open for very long to have enough light for a good picture. 

This means you can take a shot quickly. 

But it also that means that the depth of field is narrow. 

An Aperture setting of f/22 lets in a smaller amount of light because the opening is smaller.

Hence, you need to have the shutter open for longer to get enough light. 

You have to take the photos at a slower speed or Time Value (Tv).

But it also means that the depth of field is deeper.

Confused? That's okay, it just takes some practice to get used to it. Let's study some pictures that illustrate it more clearly. I took the next three shots late in the day at the exact same spot. I maintained the same ISO of 3200 for all three shots. (I used ISO 3200 because it was getting dark outside and 3200 doesn't need as much light to take good pictures.)

Okay, here's the first shot. Notice the Av of f/2.8. 

I marked where the depth of field is with the arrows. See how blurry most of the picture is? That's because f/2.8 lets in lots of light and the Time Value for the picture was 1/2000 of a second. But it also means the depth of field is "narrow." 

How do I remember? I think of f/2.8 as 2.8 inches of clarity. No, the 2.8 doesn't literally mean inches of clarity, but it's my trick to help me remember. This means that f/22 would have 22 inches of clarity. 

f/2.8 = narrow depth of field

f/22 = larger depth of field

Now, compare the f/2.8 shot above to the f/10 photo. Again, the ISO is the same, but see how the shutter was open for longer? I took this picture in 1/160 of a second.

And there's also a larger percentage of the photo in focus. But the house in the far background is still somewhat blurry. 

Finally, look at the third shot. F/22 meant it let in the least amount of light so the shutter was open for 1/30 of a second, longer than the first two shots. But most of the picture is in focus. 

Are you starting to get the idea? 

Today's Tip: The Aperture Value (Av) controls the depth of field for a photograph. 

F/2.8 lets in the most light and has the narrowest depth of field. 

F/22 lets in the least amount of light but has the deepest depth of field. 

When you're in point and shoot mode on your camera or phone, you don't have control over the Aperture. But if you turn the dial on your DSLR to Av mode, you can control it. 

CELL PHONE USERS:  I found out something interesting. There are apps that you can download for free or for a couple of dollars that allow you to control the Aperture Value on your smart phone! I'm going to research this some more and will let you know next week what I find. One company gets to use any of your images so I am planning on reading the fine print of the apps.

And as I've said before, you can control where your camera focuses by taping the screen. 

BLOGGERS: Talking about focus and depth of field can apply to your blog or inspire a post. 

IDEAS: Are we frustrated in life because we can't seem to get a particular area in our lives in the proper focus? Maybe we need to spend time learning how to focus on what God wants us to focus on. We need a good app that will allow us to do what we need to and see it clearly. Maybe that app is the bible. Or could it be learning from someone with more experience. 

I would love to hear more ideas from you! 

Next week will be the final part in this series and will help you see how to apply your new found knowledge to take better pictures! 

Assignment: Grab your camera and put it on Av and test it out! Play around with some shots so you get a feel for using the Av setting!

Hope this tip helps! 

Keep on clicking!

Mary

 TWEETABLE: What is depth of field and what does it do? Click here to Tweet.