I’ve been asked several times now, “How do you get the subject in focus but the background looks blurry?” So, I thought it would make for a good blog post! Here’s an example of what I mean:
See how his eyes are sharp, but the sides of his face and shoulders are starting to fall out of focus? And as far as the background, it’s hard to tell what exactly it is. Having a blurry background really makes the subject stand out. So how do you get this nice blurry background? Read on…
I hate to just jump right into a single variable for creating a picture, but I will anyway! Truth is, there are three main factors to think about when you are take a picture to get the correct exposure: ISO, Shutter Speed, and Aperture. For this discussion, we’ll just talk about aperture. I’ll save the others for future posts! Photography is all about light – how much or how little light to let in to get the correct exposure. The three variables I mentioned (ISO, shutter speed, and aperture) all work together to create a correct exposure. So it’s important to know that you can get a correct exposure with multiple settings. The settings affect each other, but if you want to use a different aperture, you can do that. You will just need to adjust the other settings as well to get a correct exposure. That being said – let’s jump in!
A picture with a blurry background is said to have a shallow depth of field. Meaning that only a small slice of the z-coordinate (depth) is in focus. The variable that gives me that smooth blurry background and that shallow depth of field, is the aperture. Aperture refers to the size of the opening in the lens. The measurement of that opening is called the f-stop. The opening in a lens is made up of some blades that can open to different sizes. The f-stop measure those sizes, but the smaller the f-stop, the larger the opening. For example, an f-stop of f/1.4 is a very large opening in the lens, while an f-stop of f/22 is a very small opening. So, f/1.4 lets in alot more light quickly than an f-stop of f/22. It’s for that reason, that lens’ that go down to an f-stop of 1.4, 1.8, 2.8 are referred to as “fast” lens’. These large (but small number) f-stops are also what give you a shallow depth of field, or blurry background.
Ok – so let me back up just a little. How do you tell what f-stop a lens can use? Not all lens’ can use a really large (small number) f-stop. The larger the available aperture, generally the more expensive the lens. Lens’ usually have a range of f-stops that they can use, and you can see what the largest (smallest number) aperture the lens can use by looking at the side of the lens.
This lens is able to use a maximum f-stop of f/1.8. Remember that f/1.8 is a large opening and that will provide a nice shallow depth of field. Let’s take a look now at the actual difference the aperture makes. Here are several shots of the same thing, taken at different f-stops:
See how the shot at f/2.8 has just a narrow slice of the depth in focus? And compare that to the shot taken at f/5.6, and f/22. See how as the aperture decreases (the number gets bigger), more of the image is in focus? So if you want that nice blurry background, you want to use the largest (smallest number) aperture available. A good way to play around with this on your digital SLR camera, is to use aperture priority mode. On your camera dial, you have alot of options – from totally manual (where you make all the decisions) to totally auto (where your camera makes all the decisions). One of the options is aperture priority (usually indicated by A, or AV on the dial), where you decide what aperture to use and the camera will set the rest of the options. If you want to play around with the depth of field, set your camera to A or AV mode and then use the dial to change the aperture to the lowest number available. Remember that this will be the largest opening the lens is capable of.
Ok, so what does all this mean for general use???? When I am shooting portraits, I like to have a really blurry background. I want my subject to be the main focus – so I shoot wide open (the largest aperture I have). On my favorite lens, this is f/2.8. I would say anywhere from f/1.4 – f/5.6 is good for portraits. For shooting a group of people, I might use an aperture anywhere between f/4 – f/8. When on vacation shooting landscapes, I would probably use anywhere from f/8 – f/22. These, of course, are not hard set rules – just my personal preference. Play around with the different options to see what you like!
One thing to keep in mind is that when you are dealing with a very narrow depth of field, you have to make sure you are focusing on the main point of focus, because the rest of the image will not be as sharp. If you are photographing a person, this is usually the eyes. When you are dealing with a small depth of field, you have very little room for error on your focusing. Also, keep in mind that there are other factors that will affect how much of the image is in focus. The focal length of the lens, as well as how close you are to the image is important as well. For example, if you fill the frame with your subject, the background will be somewhat blurry, even with a smaller (larger number) aperture. Anyway, I think that’s enough for one post! Hope this helps answer how I get a blurry background. And, just a little disclaimer – I don’t consider myself to be a really technical person, so I didn’t get into all the physics and optical reasons why all this is true… I just wrote what I know in (hopefully) simple terms. If there was anything you weren’t clear on, or still have questions about, please don’t hesitate to email me! I would love to help if I can!
~Until next time…