Just When You Think You Understand Depth of Field

Depth of Field is one  of those concepts that most budding photographers come at in a series of stages.

First, there’s just getting your head around what Depth of Field means. To keep it simple, if you don’t know what depth of field is, we generally think about it as the distance in front of and behind where we focused that remains acceptably sharp. Close-up portraits with blurry backgrounds usually have very little Depth of Field. Wide landscape scenes are often acceptably sharp from the closest object in the frame all the way to infinity.

Second, most beginning photographers learn to gain some control over depth of field (DOF) by changing the aperture of their lens manually (in Manual or Aperture Priority mode on your DSLR). The wider you open your aperture, the less DOF you get.

Third, it eventually dawns on photographers who concentrate on controlling DOF that you don’t always get the same DOF with the same aperture and you begin to understand the other variables in play that give you more or less DOF (sensor size, focal length, distance to subject).

Fourth, you may get really technical and look up the mathematical formulas to calculate DOF and realize that it’s all kind of a guess because how much DOF you get ultimately depends on the size the image is displayed at, how far away you are viewing it from, and how good your eye sight is.

At this point, you may fall into the trap of believing you fully understand DOF and you have all the knowledge you need to get as much control as possible over DOF in your photography.

Then, perhaps one day you discover the mysterious Tilt-Shift lens, which throws everything you know about DOF completely, well, tilted.

Here’s an example. With a normal lens, we expect the focal plane to be perpendicular to the camera sensor. Therefore, everything that is the same distance from the camera should be equally sharp. Take a look at this image:

What is acceptably sharp forms a wedge that runs roughly parallel to the ground rather than a plane that spans the entire angle of view and runs parallel to the camera sensor.
What is acceptably sharp forms a wedge that runs roughly parallel to the ground rather than a plane that spans the entire field of view and runs parallel to the camera sensor.

This image is straight out of the camera with no editing (it was also in a bracketed set of multiple exposures for the purpose of doing a composite; I just happen to like the slightly darker exposure the best for an example).

Notice the plane of critical focus doesn’t seem to be a plane at all. It’s more like a wedge shape that runs parallel to the ground. And the area above and below the wedge that is acceptably sharp is thicker closer to the camera than further away—check out the closest tree trunk and how much of it is acceptably sharp. As you go back into the image, less and less vertical distance is sharp.

Notice that the people on the bench are sharp, but the tree at the same distance to the left of them is rapidly falling out of focus. I particularly like this composition with this effect—it creates a tunnel effect that leads the eye straight to the people on the bench.

Here’s another example, also straight out of the camera. In this case, the focus was on the face of the sculpture, but the body falls out of focus even though it is the same distance from the camera. In this case it has the effect of a vignette created by blurring the edges. But notice that the distant trees directly behind the sculpture still look acceptably sharp at the height of the sculpture’s head.

Shooting this sculpture relatively close on a tilt yields a sharp face and blurred legs.
Shooting this sculpture relatively close on a tilt yields a sharp face and blurred legs.

In the next example, the sharper focus on the flowers vs the fountain keeps the eye lower, noticing the garden more. This is actually a “normal” use for a tilt shift lens—creating lots of DOF at a given height off the ground. This works really nicely for fields full of flowers, for example.


Another popular use for the tilt part of a Tilt-Shift lens is miniaturizing a scene. This is a test shot through a window, but you can see how the shifted DOF causes the brain to perceive the scene as being a miniature version of a real scene:


Once again, notice how the bricks to the right of the window are in focus, but as you get closer to the bottom of the window, they fall out of focus.

Now, you might wonder why you would buy an expensive lens in order to create these effects in camera given that this effect can be created in Lightroom or Photoshop. Truth be told, I would not buy a lens for the Tilt effect. It’s the shift effect that makes the lens worth it to me. We’ll talk more about that in another post . . .

Lesson 107: Depth of Field Through the Lens

I taught a Beginners class on macro and close-up photography on Saturday.  Macro teaches us a lot of great skills as photographers.  Because shooting subjects life-sized or bigger magnifies the mistakes we might get away with if our subjects didn’t loom so large on our sensors, macro serves to remind us and help really bring home some basic photography concepts in a whole new way.

Depth of Field is of primary concern with macro photography.  When you’re shooting practically on top of your subject, DOF is reduced to fractions of an inch–sometimes DOF is so tiny that it’s easier to think of it in millimeters, even for metric-adverse Americans.

One of the things that often confuses beginning (and even more experienced) photographers is that the depth of field you see when you look through the lens is not the depth of field you’ll get when you create the image (unless you happen to be shooting with your aperture wide open).

For example, during class, I was shooting with the Canon 100mm f/2.8L IS macro lens.  When I looked through the lens at a dandelion, this is what I saw:

The inside of the dandelion (f/2.8)
The inside of the dandelion (f/2.8)

Pretty cool, huh?  When you are looking through the lens, the aperture is wide open regardless of what aperture setting you have selected for exposure.  This allows the maximum light through the lens for you to see as well as for functions like autofocus to work better. 

Some cameras have a DOF preview button that stops the aperture down to what you’ve set it at so you can theoretically tell how much DOF you’re actually going to get.  I find this button to be only marginally useful.  I rarely can tell how much DOF I’m getting by pressing it, partly because of the loss of light.

Instead, I tend to take a shot and use a magnifying loupe to look at it on the LCD.  I may also zoom into the image to enlarge it for more careful viewing.  Then I decide if I like the DOF I’m getting and adjust if not.

In the next example, I shot the same dandelion at f/16 instead of f/2.8 (as in the first example).  Notice how we see the full ball of fluff instead of getting a horizontal view of the inside of the dandelion seeds?  That’s because there is enough DOF for the foreground portion of the seed ball to not blur completely out of view.

Same Dandelion at f/16
Same Dandelion at f/16

Personally, I find the very shallow depth of field more interesting in this case–it’s like having a view of the inside of the flower.  However, if I wanted a shot of dandelion that looked more like what we see in life, the second example would be my pick.  In fact, I’d probably want a little more depth of field to keep the tufts of the closest seen “fronds” sharp.

Lesson 102: DSLR Macro Photography

Since I answered a question about macro photography with the iPhone on our Facebook page yesterday, thought I’d do a more detailed follow up on macro with a DSLR version–my apologies for using the iPhoneography blog for a DSLR example.  For the iPhone version, check out Lesson 37:  Small Subjects.

Macro (in Canon terminology; micro if you’re a Nikon shooter) photography is probably best understood as getting really close-up to small subjects.  So close that the subject is life-sized or larger on your camera’s sensor.  It allows us to capture details that are often surprising to those of us who can’t see that well without our reading glasses.

The challenge is that all lenses have something called a minimum focusing distance.  Macro (or micro) lenses have short enough minimum focusing distances to allow you to get up close and personal with a 1:1 ratio, meaning if the subject is 10mm wide, it occupies 10mm on your sensor.

If you don’t have a macro lens, you can use extension tubes to make your minimum focusing distance much smaller, allowing you to get much closer.  Extension tubes can also be used with a macro lens to get larger than a 1:1 ratio.  Extension tube sets run from about $20-200 with the low-end being full manual and the high-end supporting the lens electronics.  With the low end version, you are likely to be stuck with a wide open aperture as the camera and lens won’t be talking to each other.

Since this blog is normally used to post simple lessons on photography you can do with your iPhone, I’m going to try to minimize the tech talk here.  But, depth of field is important in macro photography.  Depth of field refers to how much of the image is acceptably sharp in the 3rd dimension of your image–that is, front to back of the scene.

Getting up close to a subject means your depth of field is minimal even with the aperture stopped all the way down.  Sometimes backing up a bit and going more for a “close-up” shot vs a true macro image yields a more pleasing image as a result.  I frequently use a very small aperture opening (f/22ish) and opt to go “close-up” rather than true macro to increase depth of field.

Your Assignment:  I’ve included some examples of my own experiments.  There are many better examples out there from serious macro photographers.  Google macro photography in Google images and see what you get–it’s like a whole new universe living right under our lenses.  Check it out and see if this is a form of photography you’d like to experiment with.  If so, for iPhone shooters, consider getting a macro attachment lens (see Lesson 37).  For DSLR shooters, check out extension tubes as a cheap way to turn a lens you already have into a macro lens.  If you have an advanced point-and-shoot, you may also want to check out whether a macro attachment is available for your camera.



Lesson 51: The Rule of Focus

In yesterday’s lesson, we talked about holding still.  The reason holding still is important is because of the Rule of Focus.  The Rule of Focus was once stated to me by a photography instructor as:  “If at least one thing isn’t sharp, your image will fail.”

If you’ve been following along since the beginning, you may recall that in Lesson 4, I talked about a photograph where nothing was sharp, yet it is considered by many to be among the most iconic rock and roll photos ever taken.  So, just like all other “rules,” this too can be broken.

That said, most of the time, it’s true that blurry photos don’t work.  In fact, getting sharp pictures is what drives many photographers to spend thousands of dollars on expensive lenses to get the sharpest image possible.

There are multiple parts to achieving focus.  We talked about motion blur caused by a moving camera in yesterday’s lesson.  We also talked about motion blur caused by a moving subject in Lessons 31 and 32.  Today, we’re going to talk about Depth of Field.  Now, I alluded to depth of field in Lesson 30 when we explored using a Hipstamatic lens that puts only a small portion of the photo in focus.  We also talked about depth of field in Lesson 41 when we talked about putting a human subject far from the background to increase background blur.

Today, let’s talk about some of the benefits of depth of field we get automatically when we shoot with an iPhone.  The easiest way to think of depth of field is to think of the scene you’re shooting.  The scene is 3 dimensional even though your photo has only 2 dimensions.  If you were to lay a ruler on the ground from the front of what you can see to the back of what you can see, the distance that remains in focus in your photo is called depth of field.

The point where sharpness begins is usually a bit in front of where you focused.  The point where sharpness ends is usually about ⅔ of the scene back from the point where you focused.  With the iPhone, the depth of field is far greater than with a DSLR camera with comparable settings because the sensor is so small.  This is a weirdness about depth of field–how small the sensor is affects depth of field in ways that are surprising if you don’t go into detailed, technical explanations about how light works to create images.  And, I promise, I won’t.

Here are the things that are important to remember:

  1. If you’re shooting a landscape, you generally want the photo to be sharp all the way from the front to the back.  To achieve this, try to keep objects closer than 10 feet out of the frame.  Then, select the closest object in the frame for focus.  The background will usually remain reasonably sharp.
  2. If you’re shooting a person, you generally want the person to be really sharp, especially the eyes, and you don’t care about the background–in fact, it would be better if the background were out of focus.  Focus on the person’s face or let the camera use facial recognition to achieve focus.
  3. If you’re shooting something up close, like the flowers I used in yesterday’s lesson, remember that you have to be a certain distance away to get sharp focus.  You might notice that the petals in the following photo that are closest to the camera are not sharply focused.  That’s because they were too close.  By backing away, you can get the entire bouquet in focus when you select the closest petals.

Your Assignment:  Choose a subject you’d like to have completely sharp.  Move closer and further away to determine how close you can get before the foremost part of the subject remains blurry.  Experiment with selecting different focus points to see the best place to choose focus to get the entire subject in focus.  Also try taking pictures of your favorite person to see if you can get their face sharp.  Don’t forget about the Rule of Holding Still.  If you have a landscape you can shoot, see what happens when you tilt the phone so the closest object is at least 10 feet away and you focus on that.  Try it again focusing far back in the scene and again focusing very close.  Which images have the most depth of field?  Which ones do you like best?

Lesson 46: Flower Power

For today’s lesson, I used Hipstamatic with the Helga Viking Lens and the Black Keys film.  What I’d like to focus on (sorry for the pun) is something called depth of field.  Now, if you’ve read my About page, you know that I’m not allowed to explain technical stuff in this blog.  I’m going to try to keep this as simple as possible:  depth of field is what we call the distance from front to back of the scene that is in focus.  Now that I’ve said that, I’ll warn you that that’s not entirely accurate, but let’s just leave it at that before I get into trouble with Gina.

When we looked at taking portraits in Lesson 41, we talked about wanting to keep some things in focus and other things not in focus.  That’s what depth of field is all about–how do you get what you want in focus without getting other stuff in focus?

One of the painful things about the iPhone (or any other smartphone camera) is that you have very little control over this whole Depth of Field thingy.  But let’s look at what happens when I use Hipstamatic to take some very close-up photos of flowers.

In the first photo, I was so close to the group of bright yellow flowers, the reflection off of them creates a haze around the blooms.  Part of the haze is caused by soft focus on all but one flower hiding in the shadows.  While I usually like sharp photos, there is something about this hazy effect that appeals to me.

In the second photo, the leaf in the foreground is what’s in focus.  The softer focus in the other leaves and the background fence cause the leaf and fence patterns to start to look a lot like each other.  Again, while I would normally consider this a failure because of the limited focus, there’s something appealing about this to me when combined with the Hipstamatic effects.

In the third photo, the blades of grass are very sharp in the foreground, but only a few of them.  The rest blend into a mass of haze.  I’m still trying to decide if I like this or not, but it’s a good demonstration of what we would call a shallow depth of focus–only an area a couple of inches deep in the scene is in focus.

The fourth photo really brings this effect home.  The small, tall flowers in front are sharp while the big flowers in the background are soft.  I want to love this photo, but I would love it more if the foreground flowers were lighter and stood out more.  The background flowers would create a nice backdrop if there were more contrast between the background and foreground.

The fifth photo breaks one of the rules of photography.  That is, don’t have stuff in the foreground that’s out of focus.  Notice the big white flower completely blurred in the lower right.  I like this photo anyway.

Finally, my favorite, the sixth photo focuses sharply on an unopened bud with a large bloom out-of-focus in the background.  I would prefer this photo in a rectangle so that the little leaves around the bud weren’t cutoff, but I like that it’s less expected for the focus to be on the unopened bud than on the fully opened flower.

In all of these examples, I had only one way to control what was in focus and what wasn’t–distance to the subject.  By getting too close to some subjects, they were out-of-focus (like in photos 1 and 5).  Or, by getting just far enough away to focus sharply on the thing that was closest, I left the background out of focus like in photos 2, 3, 4, and 6.

Your Assignment:  See what happens when you get very close to a subject.  Pick a flower garden and shoot away.  Can you get the subject in focus?  How many other things are in focus?  Can you get closer?  When do you start to have problems getting the closest object in focus?  Do you notice how far away the background objects need to be before they fall out of focus?  Which do you prefer:  out-of-focus foreground objects or out-of-focus background objects?