Understanding depth of field

Using the depth of field

Depth of field (commonly referred to as DoF) basically determines how much of an image is in focus. You’ve most likely seen those amazing photos where the subject draws your attention right away and other things are a bit blurred. This is achievable by adjusting the DoF.

Technical part

The bigger sensor and the faster lens are used, the easier it is to manipulate the depth of field. In photography “fast” lens describes the one that allows you to use faster shutter speeds without a tripod. To make it simpler – fastest lens has the lowest F/number. For example F/2.8 lens is faster than F/4.

In order to get a blurry background you need to set your F/number to the smallest possible. This is when you need to reduce your shutter speed and/or crank-up your ISO number so your image doesn’t come out black. ISO number increase gives us some digital noise, so it’s preferable to go down on shutter speed if you can.

The technique

It’s all about practice and your camera/lens combination.  You really need to experiment quite a bit to find your ideal settings for each situation. To get better understanding of your equipment depth of field you can do a simple test shoot. And here is how:

1. Put your camera on a tripod near by a long fence or a wall on a sunny day. You can hand hold it but then make sure that you shoot from the exact same point. Main point is to get enough light and to have something long to shoot and shooting point has to be the same.
2. Set your zoom to minimum, your F/number to the smallest and take a shot of a fence or a wall. So it looks like it runs from you and away.
3. Increase your F/number by 1 and take the exact same shot from the exact same place.
4. Repeat point 3 till you get to your maximal F/number.

Are you getting the point? Yes, you need a set of the exact same photos of the exact same wall from the exact same place. The only difference between them should be the F/number. Then get back home, upload them in to your PC and compare how blur of the end of the wall changes from the lowest to the biggest F/number. That’s how you can determine your camera kit depth of field.

Photo editing software

There is also a way (there always is) to achieve similar effect by using photo editing software. You can blur the background using one of many filters in Photoshop – it’s the quickest and the simplest one. There are many more, you will get to know those as you explore capabilities of the software. The main thing to remember is that blurring the background in editing software is way easier than it is to bring it back to sharpness. So, it’s a good practice to avoid overwriting the original photo and keeping it safe in case if you need to roll back the changes.