Exploring how to use Bokeh

- As the aperture in your lens gets wider, depth of field in your scene gets more shallow. If you are not comfortable with that concept. If that's a total mystery to you. You need to go check out my "Foundations of Photography: Exposure" class, which will walk you through all of the basic rudiments of photographic exposure. Aperture size and depth of field, is one of those rudimentary things that you really have to have command over to have the most artistic and creative expression available to you as you're shooting. Now, as depth of field gets softer we tend to think that, "Oh that means the background's getting blurry." But there's actually a...

Aesthetic to that blur. There's a quality to that blur that maybe you haven't paid attention to. That quality is called bokeh. It's a Japanese word that translates roughly from blur, or haze, or blur quality. It's simply that, a measure of the aesthetic quality of that blur. And you may think, "The aesthetic quality of a blur, "how can a blur have an aesthetic?" Well, this week on The Practicing Photographer, we're gonna look at that. I have here an image shot at f2.8. Typical shallow depth of field situation.

I'm shooting a portrait. I want to blur out the background to bring more attention to my subject, so I chose a wide aperture, a 2.8 aperture. And the background is soft. But, take note of how the background has softened. It's not just out of focus. These bright highlights in here, these specular highlights, have turned into big circles. If I was to take a sharp image and throw it into Photoshop and just apply a blur filter, I wouldn't get that. I wouldn't get some things becoming larger. I wouldn't get highlights becoming larger. I would just get the whole thing becoming soft focus.

So, this is part of the quality of the bokeh of the lens that I'm having. When we speak of bokeh, we often describe, "Oh that lens had great bokeh. "The backgrounds were really buttery "and creamy and smooth." All of these things. Basically, if you would use words to describe peanut butter, it's the same thing for describing bokeh. However, bokeh has some additional concerns. One is how the the highlights expand. Do they blow up as circles, or as more polygonal shapes? Depending on how many blades there are in the shutter of your iris, that can change the shape or quality of the circle.

I'm gonna go now to the same image shot at f1.8. Things have changed a little bit. Here's 2.8. 1.8. The circles have gotten bigger and as they've gotten bigger they've become more diffuse. Some other things have happened though. Here, I can... I've got background shapes of a particular size. Notice that the lawn has gotten more diffuse and spilled out more. Again, if I was to just apply a blur filter to an area in my image editor, for the most part, geometric shapes would stay the same size, it's just they would lose detail and their edges would get soft.

Here they're radically changing how much shape they take up. And my circles are a little less round than they were before. They're getting some hard edges on them and they're taking up more space and they're getting a little more oval. Watch what happens when I go to f1.2 on this lens. These are all three shot with the same lens. Wow, my highlights have gone completely... Football shaped, I guess is what that is. Football standing on end. Obviously focus is getting much, much softer and it looks like my focus was off a little but here. Her eyes are not sharp, as compared to here. That's probably because I was focussed on the bridge of her nose or something.

But really I'm just concerning myself with the background. I am getting defocussing in the front, but I have no highlights there, so there's not really much change from one image to another. So these are aesthetic considerations I wanna take when I'm shooting. Do I like the quality of the highlights at 1.2? Or do I wanna stay with the lens stop down a little bit because I prefer circular highlights? And you may think, "Oh great. "Something else to think about." I don't spend a lot of time thinking about the shape of my highlights. If I am going to commit to shooting soft with a particular lens for a long session, say a long portrait session, I might take a test shot, look at the highlights in the background, see what shape they are.

Do a couple of other test shots, see if I like one more than another and then just commit to that for the rest of the shoot. But this is also something to consider when you're comparing lenses. If you've got a choice between a couple of different 15 millimeter lenses, say, are both of them fast? Then, maybe you wanna look at the quality of the defocus. The smoothness of the backgounds. The quality of the highlights and so on. Finally, I went to think about how much detail do I want to preserve? This background, the 2.8, is a much less abstract background, than this background at 1.8... I mean at 1.2, which has turned into just a bunch of smeary shapes.

So that's something to think about. A lot of times we go, "I want shallow depth of field, "I'll just open my aperture up all the way." Well, when you do that, you're committing yourself to a very abstract background, with really big highlights. If the highlights get too big, they may compete with your subject matter. They may become white enough and big enough that they become magnets for your viewer's eye. So it's important to think about whether you want, maybe a less abstract background and smaller highlights. If you've got a selection of lenses, it's worth putting them on your camera, going out, setting up a shot like this, try to find a shady area somewhere, put your subject in it and make sure there are some bright highlights in the background.

Cars throw off really big specular highlights. They're a great way to see exactly what your lens is gonna do, when the aperture is wide open. And that will give you a better idea, once you're out shooting with the lens, what kinda results you can expect, when you're shooting shallow. Shallow depth of field is a critical compositional tool. It's a big part of our vocabulary, as photographers. And bokeh is a big part of the aesthetic of shallow depth of field. So it's important to understand how it changes from aperture to aperture and how those changes play out on your specific lenses.