Photography 101: Boke (Depth of Field)

Today's Blog will cover example of Boke.

By the way, this is intended to build on Cheryl's very well put together description of DOF (depth of field). I suggest you take a peek at it before reading this unless you already feel you have a pretty good grasp of it.

Boke is the out of focus properties of a lens, also equal to the resulting out of focus areas in an image produced by that lens. This relates entirely to how DOF is used when taking an image.

Just to clear up some immediate confusion...you'll almost always see the word written as bokeh. This is actually a transliteration with the 'h' added to sound out the word for us Americans (*wink*). Boke is a Japanese word that means 'fuzzy mind' (er...basically). Boke is pronounced phonetically as follows: Bo-Kay (i.e. bo as in boat and kay as in cake).

Just a quick teaser: Why is a word meaning fuzzy mind being applied to photography...well as you may have realized we see more horizontally than vertically, which should be no surprise as our eyes are set apart side to side (ever wonder why big budget films are shot horizontally?). Anyway...whatever you are focused on...the rest really isn't blurry, but it also isn't clearly present. Practically speaking, a shot making good use of DOF can duplicate this phenomenon. Neat, huh? :)

Anyway, let's get to the pics. Here's a shot of building on seattle's waterfront. It uses wide DOF so there is little or no Boke here.

Sharp, sharp, sharp! When you are photographing big things, cities, buildings you'll often want a wide DOF. The same is true for the most part when shooting interiors of homes. You want to keep things crisp. As Cheryl pointed out, DOF is controlled by your aperture. Big aperture (small number) = small DOF. Small aperture (big number) = big DOF.

So let's look at some examples of photo's that employ Boke.

Subject front, boke rear. Film plane parallel to subject:

Here's a pretty standard wedding shot. The background is not only cluttered and unnecessary but including it would really distract from the bride and groom. We really want to focus just on those two.

You might notice I've given the bride an extra little priority here by providing just enough DOF to keep her sharp, the groom is going a bit soft.

BTW, if it hasn't already occurred to you; DOF is one of the main ways photographers define the subject of their photographs. For the most part a good photograph always has a clearly defined subject. DOF is essential tool in that regard.

Here's an interesting and very common misunderstanding of DOF that I've even heard other photographers fall into. DOF does NOT define a sharp 'chunk or place' of the photograph. DOF describes instead how gradual the fall off of sharpness is. Did that make sense?

Let me state it differently. Only one tiny tiny segment of any photograph is 'sharp'. move past that and it's slightly less sharp, past it a tiny bit more and it's less sharp still. DOF tells us how fast it will get noticeably blurry. Wide DOF means it will take a good while till we notice it getting really blurry. Small DOF means it will get blurry very quickly and so on.

Subject front, boke rear. Film plane tilted to subject:

Since the fall off of sharpness happens in a fairly linear way, parallel to your film plane, if you tilt your camera you automatically shift the boke along with it.

While this may appear obvious to some, you can create some really nice compositions where you use blur to enhance what otherwise would be a pretty standard image.

In this case if I had shot the subject straight on, along with his eyes and face most of his body would have been sharp. Not terribly interesting.

Instead we get a really nice fade out of his lower body and the riding car. This leads the viewer to focus immediately on the eyes of the subject, which is where they should be. :)

Subject middle, boke rear AND front. Film plane parallel to subject:

Something people often forget is that they can use a narrow DOF to hit a subject in between forward objects and rear objects. This allows for a world of creative images.

One of the best aspects of using boke this way is the ability to impart intimacy.

When I see the photo to the left I feel, for a second...that I am part of the boys 'moment'. Maybe in a way no one around him sees.

Not all boke is created equal:

If you've stuck with me thus far you are doing great. We are almost done.

Take a look at the image to the left. Look closely at the specular highlights (bright spots) in the out of focus area.

If you are the observant type you might notice that they are all basically the same shape.

The quality of the blur, it's 'shape' and 'feel' or boke is defined solely by the shape and quality of the aperture in the lens.

This is one area where high quality professional lenses really shine. This image was shot with the legendary Canon 70-200mm 2.8, one of the finest mid range zooms money can buy. Mostly it's a bulky monstrosity I dislike shooting with but it produces beautiful, buttery boke thanks to it's outstanding aperture and image quality overall is unsurpassed for a lens of it's type.

Budget lenses will have less blades (4 or 5) vs. professional lenses (8-9). The results may surprise you depending on how sensitive you are to the visual distortion. Consumer lenses may at times produce pentagonal blur or have jagged harsh edges on the boke. On the other hand you may not even notice it...your mileage may vary.

One last note for point and shoot users:

I'm afraid I've got some bad news for you guys. While I won't bore you with the engineering detail, due to sensor size combined with the lenses on most consumer P&S cameras...you'll have a very hard time producing photographs with a narrow depth of field.

You see small consumer cameras tend to operate in what I would describe as A-Depth mode meaning they have hugely wide DOF in most circumstances. This is largely a constraint built in to their design and for the most part if you want to enjoy truly narrow DOF you'll need to switch to another camera.

On the bright side, while I don't follow P&S tech too closely I'd be surprised of manufacturers aren't trying their best to improve this. There may be models out now that allow narrower DOF. Time will tell.

Cheers, -B

Seattle-Photographer