Bokeh. How to blur the background of a photo?
I was digging into my hard drive and going through a series of photos I took a while ago and one of my friends that was there with me asked me “How do you blur the background in your pictures?”
This is not the first time someone asks me this question.
In photography one of the most appealing effects to reproduce and play with, is to create a photo with soft, blurry background. But how to do it?
A creamy background, commonly known as bokeh is obtained by controlling a series of aspects such as aperture, distance from the subject, focal length and sensor size. Honestly I’ve been doing it in my photos without even thinking at the proper step by step technique to obtain a nice out-of-focus and creamy background and I put down this list that hopefully can be useful to other people too. Let’s dive into it.
What is bokeh in photography?
When reading a lens review from a photography website or visiting a forum you’ll easily find people debating over what lens produces the best bokeh, what is the best shape of a bokeh and so forth.
Bokeh is the term used in photography to describe the optical phenomenon of a soft out-of-focus background. It’s a Japanese word and it means “blur” or “haze”.
It’s such an important aspect of photography, because it can dramatically change the viewer’s perception of the subject. When out of focus, highlights areas of the image become soft and ghostly circles of light, very pleasant to the eye. While the subject in a photo is the protagonist of the scene, bokeh can determine how much that subject (object or person or animal) stands out from the background and it helps enhancing the 3 dimensional feel of the image. Depending on the lens bokeh can have various shapes. It can be circular, or even hexagonal. The edges of the circles can be smoother or more rough. And all this can really affect the appeal of an image.
As you may or may not know the aperture of a lens can be wide or narrow. It determines the quantity of light that reaches the camera sensor and it’s measured in f/stops. A wide aperture can be for example f/2.8 or f/4 (or even less) while a narrow aperture is f/22. The smaller the f/stop value the wider the aperture and vice versa. So how does aperture produces bokeh? If you grab your camera and set it to the maximum aperture (f/2.8 for example) this will decrease the depth of field, which very simply explained is the area within two points of acceptable sharpness in a photograph. Ah easy! So often we are tempted to choose the widest aperture to achieve the maximum blur, but I think that depending on the scene this could be a mistake. In my opinion, more aesthetically pleasing effects are obtained if some detail is left in the background to let the viewer understand or imagine the shapes surrounding the main subject. Not too much detail though, otherwise there wouldn’t be enough separation from the background and the image will look two dimensional and confusing to the viewer’s eye.
Distance from the subject
Minimizing the distance between yourself and the subject is another way of obtaining a good blurred and milky background. When you are very close the lens will focus closer and the depth-of-field will also be shallower. You can also do a quick experiment with your eyes. Even though the human eye doesn’t really do a great job in terms of creating bokeh, if you bring your finger very close to your nose and stare at it you’ll notice how the background gets blurrier. Interesting uh?
So if you are shooting at 2 meters far from your subject it’s not the same as being 50 or 70 cm (20″ or 30″) away from it. Moreover you might have noticed that the further away is the background from your subject, the easiest it is to obtain a good bokeh. This is because the depth-of-field is not a hard line after which everything is out of focus, but it gradually fades from sharp to blurred. So a background very close to the main subject will make the bokeh less obvious and the quality of your image will suffer, resulting again in a more confusing composition without clear separation between subject and its surroundings.
Despite the name, remember that focal length is not the length of a lens. 🙂
Technically, focal length is the measurement of the distance from the lens’s optical center to the sensor in the camera, when the lens is focused at infinity. It’s described in millimeters, it tells you the angle of view, the magnification and it affects the depth-of-field. The longer the focal length is, the shallower the depth-of-field will get (more bokeh). The shorter the focal length, the bigger the depth-of-field (hence less bokeh). Zoom lenses will be more versatile than prime lenses since the former have a variable focal length and you can play with it to achieve your optimal bokeh. Though prime lenses tend to have a wider aperture (f/1.4 to f/2.8). A longer focal length of for example 300mm such as the one of a telephoto lens will compress the perspective and make the background look closer to the foreground, but at the same time, at the right aperture, will make the background so smooth and it will isolate the main subject for a better result.
While the fierce “battle” amongst photographers about the impact of your camera sensor on image quality goes from the “bigger sensor is better” to “portability over resolution”, I don’t want to start yet another debate on this. Sensor size has no questions an impact on image quality, higher dynamic range, high ISO performance and definitely on bokeh and how smooth your background will be.
There’s no doubt that a bigger sensor will help you deliver a smoother and creamier background. But it’s unfair to say that small sensor cameras such as micro four thirds systems or APS-C sensor are not able to achieve excellent bokeh. You just need to know your tools, your camera and your lenses. If you look at the following images, what do you see? Isn’t that a good bokeh? Well they’re all images taken with a micro four thirds system.
This of course depends also from the quality and construction of the lens and you might have heard photographers ask “How good is the bokeh of tha lens?”
Well as we’ve seen, increasing the focal length helps decreasing the depth-of-field (DoF) and create a smoother background for a nicer bokeh effect. Obviously though, this also depends on the quality of the lens. Different lenses with the same focal length will give different results depending on their optics. The number of blades that make up the aperture of your lens are what make the difference between different lenses. In less expensive lenses you can find 5 or 6 blades whereas better quality and pro lenses have 9 or more blades on the aperture.
Other than the number of blades another factor to consider is the shape of the blades and how they are positioned. A rounded aperture will always produce a better bokeh compared to an aperture with hard corners. See it this way. The shape of the aperture’s blades will determine the shape of the out of focus area in your image. So your bokeh will either be hexagonal or more or less circular.
A lens has also to be fast, meaning that an aperture of f/2.8 (or less) is more likely to produce a better effect than an f/8, because the wider the aperture, the shallower the depth of field.
In conclusion, how do I obtain a good bokeh in a photo?
Ultimately, we’ve seen how a blurred background or bokeh is a really nice component of a certain type of photographs. It helps highlighting the main subject and making the image look more 3 dimensional. Bokeh depends from several factors and I invite you to take your camera now, and start experimenting the points we’ve discussed above one by one. Start playing with the aperture of your camera. Set it to aperture priority, it’s called mode A or Av on Canon cameras and starting from the smallest f/stop value, you will see how changing the it will give you different results. Then always using A mode, move yourself away from the subject and then get closer to it. Move around and frame the main subject (person, animal, flower or any object) in such a way so that the background is further away and again, compare the different results. Add, in the end, the focal length factor. If you have access to a telephoto zoom lens, start from the maximum focal lens and decrease until you reach the optimal length for the aperture value you are using at the distance from you and the subject and from the subject to the background. You’ll be able to produce a wonderful bokeh in no time!
I hope that I answered your question about how to blur the background on a photo and that you’ve enjoyed this post.
Don’t hesitate to ask me questions in the comments below and share with me your thoughts and your images, I really want to see what are your results!