depth of field for portraits
* I want to mention that this article has been revised after receiving a helpful comment from yz (check out the beautiful images on his photoblog). I appreciate the clarifications, we’re all here to learn…
In this day and age it’s possible to create quite beautiful photographs without fully understanding focus and depth of field. As long as your auto focus lens purrs when you hit the button and a little sensor lights up on the intended subject, you’re good to go. But, really, that’s putting out a bare minimum of effort to control focus in an image. There are certain principles that, when understood, will help you create more consistent images.
As is often the case, I try to give out information that can be understood relatively quickly and utilized immediately. Rather than dive into the deeper complexities of focus I’d like to illustrate a depth of field guide I’m conscious of when shooting portraits. At the end of this post are some suggestions for further reading.
A fairly common question is, “when photographing a group is it better to focus on the front row or the back row”? The short answer is the front row. But that’s not really the correct answer.
I’m assuming we all understand that stopping down a lens (shooting at a smaller aperture) increases depth of field, expanding the plane of focus from front to rear. What those new to photography may not realize is that, in common portrait distances and situations, roughly one third of your sharpness (depth of field) will fall in front of your focus point and two thirds will fall behind your point of focus. I had long been under the impression that this “one third – two thirds” depth of field guide applied to all photo situations but that is apparently a common misconception (and one I’ve carried for a while). This ratio is not consistent, becoming more even as we get closer to a subject. But, for this illustration of photographing people at mid-distance, I feel comfortable using this one third – two thirds method as a guide. The attached home brew illustration is my attempt to show how this works.
If you’re shooting at f2.8 and only have three inches of depth of field (sharp focus), one inch of sharp focus will fall in front of your point of focus and two inches behind it. If you’re shooting at f16 and have 18 inches of depth of field it’s the same formula: six inches in front and twelve inches behind the point of focus will be sharp. Focus rolls off gradually beyond those points, it doesn’t suddenly become dramatically unsharp.
The big question is always “what aperture should I use”? Well, that depends on the effect you’re after and the amount your subject is being magnified. There are a few ways to figure how much depth of field you will have, a range of options to satisfy everyone from the super technician to the freewheeling creative:
1. Learn the mathematic equations governing depth of field
2. Use lenses with depth of field markings on their barrels
3. Use your camera’s depth of field preview lever, if you have one
4. Chimp that LCD with your reading glasses on and hope it’s sharp
5. Pay attention to final photo results and shoot certain subjects in a consistent way so that a feel for depth of field will be developed
In this past Monday’s video I recommended that, rather than just zooming from where you’re standing to frame a portrait, be conscious of what focal length your lens is set to. I like to use 100mm lenses for portraits. First, I like this focal length because it is flattering to the subject (no wide angle distortion but also not the very “flat” perspective of very long focal lengths). It also helps me when it comes to previsualizing the depth of field I will have in the portrait. I’ve developed an innate feel for how much focus there will be at f4 compared to f8 when standing at a comfortable distance from the subject. It’s familiar and allows me to concentrate on other things rather than, well, focusing on focus. I always look critically at the final images to confirm I’m on the right track.
If you’re ready to take your depth of field learning to the next level, here are a couple of great posts:
Beginners check out Edberg Photo’s Setting Depth of Field Tips.
For the more advanced it’s another great opportunity to turn to the wealth of information at Luminous Landscape.
Sorry to say this, but this often heard concept of 1/3-2/3 is simply not true. In fact there are really rare cases when you have these numbers.
The more you stop down a lens the more proportion of depth of field goes behind the sharp plane of focus and less in front. Just check and older lens or a rangefinder lens where the DOF is indicated and you’ll see the above said is true. For example if you stop down well, you may have a plane of focus at say 4 meters, DOF behind until infinity, in front say 1-1,5 meters then you immediately see that the 1/3-2/3 proportion is not true.
The other case is at close up distances (macro) at any apertures and any focal length, where the proportions are almost exactly 1/2 in front and 1/2 behind.
Though as far as your article is concerned, in a typical portrait situation where you have a subject distance about 3 meters, a longer lens and medium or wide aperture, this 1/3-2/3 proportion is approximately true, it can be used as a rule of thumb. But as a general photographic rule it is simply an old misconcept.
Anyway I love your blog, find it very useful, so please, don’t take my comment offensive.
best
z
No offense taken, yz, I really appreciate you pointing this out. I checked out the mathematics and see that my long held belief (that 1/3 – 2/3 always applies) is actually errant, just as you’ve said. A number of other articles I’ve found also mistakenly state the 1/3 – 2/3 guide as an absolute rule. I’ve taken the time to revise my post to relate this, it’s important. I hope it now reflects a more accurate picture of how / when to think in terms of 1/3 – 2/3.
And I’m glad you like the blog, I appreciate having educated readers to keep things on track!
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Another resource I like for DOF is http://www.dofmaster.com/doftable.html
You can then plug in your camera, favorite lens, f-stop, etc and see just what the calculated DOF is.
For me this information was both revealing and enlightening.
Interesting timing, I was just doing some looking around for help in explaining DoF to someone in a Flickr thread. I referred them to David Ziser’s post from a few weeks ago: http://digitalprotalk.blogspot.com/2008/08/depth-of-field-myth.html Really great info in both David’s post and the articles he links to.
To help to explain DoF to some photography students of mine I bought ExpoImaging’s ExpoAperture a while back.
It’s pretty handy but I’ve since switched to using PhotoCalc on my iPhone. It’s far cheaper and very easy to use. It’s also got some other really great features, like sunrise and sunset times for your location and a flash exposure calculator.
Excellent article and very useful information in the comments. Looks like you can download a DOF calculator to you iPhone. Not that you would use that too often, but might come in handy.
Hi Jim
I’m just jumping on to say I for one really appreciate the hard work you put into this blog.
I keep you on my igoogle for updates with my other favourite blogs from the likes of AltF and Strobist.
Cheers mate
BK
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