I know you want me to tell you a secret or a gadget that will get you great background blur easily. Don’t worry – I will do so – but first please indulge me while I stress the fundamentals.
Aperture Settings
As you likely already know, getting a blurred out background or shallow depth of field (some call it bokeh) is largely a function of using a large aperture setting. You want to use the smallest f/number that your lens allows. The measurement is a ratio so the small measurements mean large apertures (counterintuitive, I know). The maximum aperture depends on the lens, and in many cases it will be something like f/4. The fastest zoom lenses (and when photographers refer to fast lenses, they mean lenses where the aperture opens up really wide) open up to f/2.8. Those are the sorts of numbers you are looking for.
If you are using the lens that came with your camera (called a kit lens) this will have a maximum aperture of f/3.5 -5.6. That means that the maximum aperture when you are zoomed all the way out is f/3.5, but as you zoom in the maximum aperture setting gets higher and higher until it reaches f/5.6. If you are curious as to why that happens, it isn’t that the aperture size is changing – it is actually staying the same size. But the way aperture is measured is as a ratio (aperture size to focal length) so as you zoom in your focal length is changing, resulting in a different measurement. (That really doesn’t matter for purposes of this answer, but it confuses a lot of people so I wanted to address it).
Relative Distance
Step one in getting a blurred background is to use a large aperture, but it doesn’t end there. Next, you need to put some distance between what you are focusing on and what you want blurred out. Very often people have problems with this and when we take a look it is because they have things in their picture right next to each other. The further away you have things in your picture from whatever it is you are focusing on, the more background blur you will have. Things do not immediately go from sharp to blurry – instead there is a gradual fall off. The more room you provide for this process to happen, the more blur you will get.
Next, try to keep the thing you are focusing on relatively close to you. The farther things are away from you, the more the camera has difficulty distinguishing distances. If you want to see this for yourself, look at the distance scale on the top of your lens (if it has one). You’ll see when the distances are short, there is a lot of room between them on the scale. As distances get longer, there is less and less room. Ultimately, you will just see a little infinity symbol, which means the camera has lost the ability to distinguish distances and everything will be in focus.
If you are having trouble make it work, go outside and take a close-up picture of a street sign, but make sure there is at least a little background in the shot. Obviously, you should use your largest aperture setting (smallest f/number). That is a good way to keep your subject close and the background far away to give this process a chance to work. From there, you can take additional shots with the background closer and closer. As you work with it, you’ll get an idea of the kind of range you need to get good background blur.
A Great Buy
Ok, with that out of the way, I will tell you something you can buy that will allow you to get tremendous background blur. The way you do that is to buy fast glass, or a lens with a really wide aperture. The trouble with that approach is that these sorts of lenses are expensive. There is a direct correlation between the maximum aperture size and how much the lens costs. In most cases, lenses with large apertures cost thousands of dollars.
There is one exception though, and it is the 50 mm lens. You can get a 50 mm f/1.8 lens for about $100. Only $100 for a lens! I know this is true for both Canon and Nikon, and I suspect there are others brands out there as well. They work great too and they are pretty sharp. Nothing else comes close to that in terms of bang for the buck.
Why are these lenses so cheap? Several reasons. First, it is a prime lens (one focal length), so it is simpler and smaller. Your other lenses will dwarf this lens if you set them side by side. Further, the manufacturers have been making 50 mm lenses for about 100 years, so they have this pretty well figured out. Finally, they are cheaply made. If you do get one, you will be unimpressed with the build quality and it will feel plasticy (but they work fine – just don’t bash it around too much, which I suppose you really shouldn’t be doing anyway).
One word of warning before you rush off to buy one. You will see other 50 mm lenses that cost a lot more. Pay attention to the aperture size and make sure it says f/1.8. You will run across 50 mm f/1.4 lenses that cost a lot more and 50 mm f/1.2 lenses that are shockingly expensive. Don’t worry about those and just get the f/1.8 version.
Once you do, you will have a lens with a maximum aperture that is super wide. To put it in perspective, the widest aperture on any zoom lens – no matter how much money you throw at it – is f/2.8. You’ll have a lens for $100 that is a full stop faster. Pick it up, put it on, and give it a whirl. You might even find that the depth of field is sometimes too shallow. And if you are still having trouble creating background blur, you’ll know it isn’t the lens’s fault. In that case, re-read the fundamentals information up top.