Depth of field

Sunset Palette, Half Dome from Sentinel Dome, Yosemite

Sunset Palette, Half Dome from Sentinel Dome, Yosemite
Canon EOS-1Ds Mark II
45 mm
2 seconds
F/20
ISO 100

What’s the point?

It seems like one of photography’s great mysteries is achieving proper focus—the settings to use, where to place the focus point, even the definition of sharpness are all sources of confusion. If you’re a tourist just grabbing snapshots, everything in your frame is likely at infinity and you can just put your camera in full auto mode and click away. But if you’re an artistic photographer trying to capture something unique with your DSLR or mirrorless camera, you should be doing your best to have important objects at different distances throughout your frame. In that case you need to get out of the auto modes and start taking control of your exposure settings and focus point.

When focusing a composition, you first need to determine whether you even want sharpness throughout the frame. While some of my favorite images use selective focus to emphasize one element and blur the rest of the scene, most (but not all) of what I’ll say here is about maximizing depth of field (DOF). I cover creative selective focus in much greater detail in another Photo Tip article: Creative Selective Focus.

Beware the “expert”

I’m afraid that there’s some bad, albeit well-intended, advice out there that yields just enough success to deceive people into thinking they’ve got focus nailed, a misperception that often doesn’t manifest until an important shot is lost. I’m referring to the myth that you should focus 1/3 of the way into the scene, or 1/3 of the way into the frame (two very different things, each with its own set of problems).

For beginners, or photographers whose entire scene is at infinity, the 1/3 technique may be a useful rule of thumb. But taking the 1/3 approach to focus requires that you understand DOF and the art of focusing well enough to adjust your focus point when appropriate, and once you achieve that level of understanding, you may as well do it the right way from the start.

Where to focus this? Of course 1/3 of the way into a scene that stretches for miles won’t work. And 1/3 of the way into a frame with a diagonal foreground won’t work either.

Back to the basics

Understanding a few basic focus truths will help you make focus decisions:

  • A lens’s aperture is the opening that allows light to reach your sensor—the bigger this opening, the more light gets in, but also the smaller your DOF.
  • Aperture is measured in f-stops, which is the lens’s focal length divided by the aperture’s diameter; the higher the f-number, the smaller the aperture and the greater the DOF. So f/8 is actually a bigger aperture (with less DOF) than f/11. Some find it helpful to think of f/stops this way: The higher the f-number, the greater the depth of field. Though they’re not exactly the same thing, photographers usually use f-stop and aperture interchangeably.
  • Regardless of the current f-stop setting, a camera maximizes the light in its viewfinder by always showing you the scene at the lens’s widest aperture. All this extra light makes it easier to compose and focus, but unless your exposure is set for the widest aperture (which it shouldn’t be unless you have a very specific reason to limit your depth of field), the image you capture will have more DOF than you see in the viewfinder. The consequence is that you usually can’t see how much of your scene is in focus when you compose. Most cameras have a DOF preview button that temporarily closes the lens down to the f-stop you have set—this shows the scene at its actual DOF, but can also darken the viewfinder considerably (depending on how small your aperture is), making it far more difficult to see the scene.
  • The zone of focus sharpness extends a greater distance beyond the focus point than it does in front of the focus point. If you focus on that rock ten feet in front of you, rocks three feet in front of you may be out of focus, but a tree fifty feet away could be sharp. I’ll explain more about this later.
  • While shorter focal lengths may appear to provide more depth of field, DOF doesn’t actually change with focal length. What does change is the size of everything in the image, so as your focal length increases, so does your apparent DOF. So you really aren’t gaining more DOF with a shorter focal length, but softness will become more apparent as your focal length increases because your subjects are magnified.
  • The closer your focus point, the narrower your DOF (range of front-to-back sharpness). If you focus on a butterfly sunning on a poppy one foot in front of your lens, your DOF is so narrow that it’s likely parts of the poppy will be out of focus; if you focus on a tree 100 yards from your lens, it’s likely that the mountain behind the tree is sharp too. (But the actual zone of sharpness will vary with your sensor size, f/stop, and focal length.)
  • Foreground softness, no matter how slight, is almost always a greater distraction than slight background softness. So, if it’s impossible to get all of your frame sharp, it’s usually best to ensure that the foreground is sharp.
Whitney Arch Moonset, Alabama Hills, California

Moonset, Mt. Whitney and Whitney Arch, Alabama Hills, California
With subjects throughout my frame, from close foreground to distant background, it’s impossible to get everything perfectly sharp. Here in the Alabama Hills near Lone Pine, California, I stopped down to f/16 and focused at the at the most distant part of the arch. This ensured that all of the arch would be perfectly sharp, while keeping Mt. Whitney and the rest of the background “sharp enough.”

Defining sharpness

Depth of field discussions are complicated by the fact that “sharp” is a moving target that varies with print size and viewing distance. But it’s safe to say that, all things equal, the larger your ultimate output and closer intended viewing distance, the more detail your original capture should contain.

To capture detail, a lens focuses light on your sensor’s photosites. Remember using a magnifying glass to focus sunlight and ignite a leaf when you were a kid? The smaller (more concentrated) the point of sunlight, the sooner the smoke appeared. In a camera, the finer (smaller) a lens focuses light on each photosite, the more detail the image will contain.

In photography we call that small circle of light your lens makes for each photosite its “circle of confusion.” The larger the CoC, the less concentrated the light and the more blurred the image will appear. Of course if that large CoC is still too small to be seen as soft, it really doesn’t matter. In other words, areas of an image with a large CoC (relatively soft) can still appear sharp if viewed from far enough away. That’s why sharpness can never be an absolute term, and we talk instead about “acceptable sharpness” that’s based on print size and viewing distance.

But how much detail do you need? For any focus point, there’s only one plane of maximum sharpness, regardless of the focal length and f-stop—everything in front of and behind the plane of your focus point will be some degree of less than maximum sharpness, and the farther in either direction a point is from the focus plane, the larger the CoC and the softer it will appear. But depending on the viewing distance, this less than maximum sharpness can still be acceptable. Every point in the image with a CoC that’s too small for your eye to discern will be acceptably sharp.

Put in more practical terms, the threshold for acceptable sharpness is pretty low for an image that just ends up on an 8×10 calendar on the kitchen wall, but if you want that image large on the wall above the sofa, achieving acceptable sharpness requires much more detail. And as your print size increases, the CoC that delivers acceptable sharpness shrinks correspondingly.

Many factors determine the a camera’s ability to record detail. Sensor resolution of course—the more resolution your sensor has, the more important it becomes that to have a lens that can take advantage of that extra resolution. And the more detail you want to capture with that high resolution sensor and tack-sharp lens, the more important your depth of field and focus point decisions become.

Hyperfocal focus

The foundation of  a sound approach to achieving proper focus for your viewing distance and image size is hyperfocal focusing, a science-based method that uses viewing distance, f-stop, focal length, and focus point to ensure acceptable sharpness for a given CoC.

The focus point that provides the maximum depth of field for a given combination of f/stop and focal length is the hyperfocal point. When focused at the hyperfocal distance (on the hyperfocal point), your scene will be acceptably sharp from halfway between your lens and focus point all the way to infinity. For example, if the hyperfocal point is twelve feet away, focusing there will give you acceptable sharpness from six feet (half of twelve) to infinity—focusing closer will soften (increase the CoC for) the distant scene; focusing farther will extend the area of foreground softness.

The most overlooked aspect of hyperfocal focusing is determining the proper CoC. Since people’s eyes start to glaze over when CoC comes up, they tend to use the default given to them by their table or smartphone app. At the very most they plug in their sensor size (a good start) and consider themselves done.

What you may not know is that the hyperfocal tables and focus distance markers on prime lenses (remember those?) that have been plugged into most hyperfocal smartphone apps assume that you’re creating an 8×10 print that will be viewed from a foot away. Worse still, they have applied a CoC that is three times larger than the eye’s ability too resolve.

That doesn’t invalidate hyperfocal focusing, but if you use published hyperfocal data (or a hyperfocal app), your images’ DOF might not be as great as you think it is (for your need). If you can’t specify a smaller CoC in your app, I suggest that you stop-down a stop or so more than the app/table indicates. On the other hand, stopping down to increase sharpness is an effort of diminishing returns, because diffraction increases as the aperture shrinks and eventually will soften the entire image—I try not to go more than a stop smaller than my data suggests.

Another downside to hyperfocal focusing is that it requires in-the-field access to data that’s not necessarily conducive to the creative process—referring to charts or a smartphone app is awkward, and likely distracting. I’m a big advocate of keeping photography as simple as possible, so while I’m a hyperfocal focus advocate in spirit, I don’t usually use hyperfocal data in the field. Instead I apply hyperfocal principles in the field.

Though I don’t often use the specific hyperfocal data in the field, I find it helps a lot to refer to hyperfocal tables when I’m sitting around with nothing to do. So if I find myself standing in line at the DMV, or sitting in a theater waiting for a movie (I’m a great date), I open my iPhone hyperfocal app and plug in random values just to get a sense of the DOF for a given f-stop and focal length combination. I may not remember the exact numbers later, but enough of the information sinks in that I accumulate a general sense of the hyperfocal DOF/camera-setting relationships.

Finally, something to do

Unless I think I have very little DOF margin for error in a composition, I rarely open my hyperfocal app in the field. Instead, once my composition is worked out, I determine the closest object I want sharp. That can be pretty much anything with visual interest (shape, color, texture), regardless of whether it’s a primary subject. If it’s close enough to hit with my hat and I want sharpness to infinity, I need lots of DOF and opt for f/16 (if I fear I might need to go smaller than f/16, I usually pull out my app to verify); if I could hit it with a baseball, I choose an f-stop around f/11; if it would take a gun to reach it (infinity: imagine a distant peak), I choose an f-stop between f/8 and f/11. Of course these distances are very subjective and will vary with your focal length and composition (not to mention the strength of your pitching arm), but you get the idea.

Sunset Palette, Half Dome from Sentinel Dome, Yosemite

A hat’s toss away: The closest pool was about 6 feet from my lens. I stopped down to f/20 (smaller than I generally like to go) and focused on the back of the pool on the left, about 10 feet away.

A baseball throw away: The little clump of wildflowers (lower right) was about 35 feet away and the trees started another 35 feet beyond that. With a focal length of 55mm, I dialed to f/11 and focused on the most distant foreground tree, getting everything from the flowers to Half Dome sharp.

Gary Hart Photography: Tree and Crescent, Sierra Foothills, California

Honey, fetch my rifle: With everything here at infinity I knew could focus on the trees or moon confident that the entire frame would be sharp. In this case I opted for f/8 to minimize diffraction but still in my lens’s sharpest f-stop range, and focused on the tree.

Why not just automatically set my aperture to f/22 and be done with it? I thought you’d never ask. Without delving too far into the physics of light and optics, let’s just say that there’s a no so little light-bending problem called “diffraction” that robs your images of sharpness as your aperture shrinks—the smaller the aperture, the greater the diffraction. Then why not choose f/2.8 when everything’s at infinity? Because lenses tend to lose sharpness at their aperture extremes, and are generally sharper in their mid-range f-stops. So while diffraction and lens softness don’t sway me from choosing the f-stop that gives the DOF I want, I try to never choose an aperture bigger or smaller than I need.

Now that we’ve let the composition determine our f-stop, it’s (finally) time to actually choose the focus point. Believe it or not, with this foundation of understanding we just established, focus becomes pretty simple. Whenever possible, I try to have elements throughout my frame, often starting near my feet and extending far into the distance. When that’s the case I stop down focus on an object slightly behind my closest subject (the more distant my closest subject, the farther behind it I can focus).

When I’m not sure, or if I don’t think I can get the entire scene sharp, I err on the side of closer focus to ensure that the foreground is sharp. Sometimes before shooting I check my DOF with the DOF preview button, allowing time for my eye to adjust to the limited light. And when maximum DOF is essential and I know my margin for error is small, I don’t hesitate to refer to the DOF app on my iPhone.

A great thing about digital capture is the instant validation of the LCD—when I’m not sure, or when getting it perfect is absolutely essential, after capture I pop my image up on the LCD, magnify it to maximum, check the point or points that must be sharp, and adjust if necessary. Using this immediate feedback to make instant corrections really speeds the learning process.

Sometimes less is more

The depth of field you choose is your creative choice, and no law says you must maximize it. Use your camera’s limited depth of field to minimize or eliminate distractions, create a blur of background color, or simply to guide your viewer’s eye. Focusing on a near subject while letting the background go soft clearly communicates the primary subject while retaining enough background detail to establish context. And an extremely narrow depth of field can turn distant flowers or sky into a colorful canvas for your subject.

In this image of a dogwood blossom in the rain, I positioned my camera to align Bridalveil Fall with the dogwood and used an extension tube to focus extremely close. The narrow depth of field caused by focusing so close turned Bridalveil Fall into a background blur (I used f/18 to the fall a little more recognizable), allowing viewers to feast their eyes on the dogwood’s and raindrop’s exquisite detail.

An extension tube on a macro lens at f/2.8 gave me depth of field measured in fractions of an inch. The gold color in the background is more poppies, but they’re far enough away that they blur into nothing but color. The extremely narrow depth of field also eliminated weeds and rocks that would have otherwise been a distraction.

There’s no substitute for experience

No two photographers do everything exactly alike. Determining the DOF a composition requires, the f-stop and focal length that achieves the desired DOF, and where to place the point of maximum focus, are all part of the creative process that should never be left up to the camera. The sooner you grasp the underlying principles of DOF and focus, the sooner you’ll feel comfortable taking control and conveying your own unique vision.


We cover DOF in much more detail in my photo workshops

Gary Hart Photography Death Valley Photo Workshop Group

Death Valley Photo Workshop Group, Zabriskie Point

:: Click for more photography tips ::

Playing with depth

Click an image for a closer look and slide show. Refresh the screen to reorder the display.

31 Comments on “Depth of field

  1. Gary…this is great information. I thought I understood DOF an focus but realize I have so much more to learn (and experiment with). Thanks for this very insightful article!

  2. Thanks for another insightful tip. Keep ’em comin’
    We can’t wait until next February!
    Bob & Bren

  3. Thank you for the awesome post Mr. Hart. Do you use these general rules in low light situations as well or would you modify them in that situation?

    • Thanks, Tyler. Yes, these principles apply even in low-light situations, which is why you should be on a tripod. In landscape photography the aperture manages DOF and never light; shutter speed manages light, and if there are motion considerations (such as wind or moving water), manage them with your ISO. DOF rules in landscape photography.

      • Thanks again Mr. Hart. I look forward to your future tips and images.

  4. Thank you very much for this Gary. I like your examples of the hat’s throw, baseball (I just think of someone else throwing it!), and gun. That analogy makes the theory easier to remember.
    Anne.

  5. Pingback: Cameras are stupid, Part deux | Eloquent Nature by Gary Hart

  6. Gary, I am now totally confused. The old saying is true, the more you think you know the less you know.

    I now think I need to back way up and learn how to focus again and where to have my focal point especially at night.
    Thanks for a great article.

    Tom

    • Thanks, Tom, though my hope was to enlighten rather than confuse. Just don’t forget that focus is your creative choice, so there’s no absolute right/or wrong. The more you understand about it, the better your ability to achieve the result you seek. Good luck!

  7. Thank you for your reply and educational articles. I am sure I will get it but I would rather have it sooner than latter. I am a perfectionist and want to get it right

  8. Gary,
    It (hyper)all finally came together. I have poured over this article several times and I finally understand. Now practice….on anything. I have a great backyard. The big sur coast 30 minutes from home and Yosemite 3 1/2 hrs.

    For landscape–Focus a little beyond your prime subject that you want in focus. Adjust F stp accordingly(hat, ball, gun). tables are not good for me nor the iPhone since I do not have one nor will I buy one—-yet. Check w/ magnification before final shot. So your article really pulled it all together after several reads!

    Thanks you several times over.

    Tom Gibson

  9. Pingback: There’s no whining in photography | Eloquent Nature by Gary Hart

  10. Pingback: From one extreme to another « Eloquent Nature by Gary Hart

  11. Hi Gary,
    Thanks for sharing and explaining a difficult concept, but essential to creative photography. I will read this quite a few times before I understand it all as my mind is whirling with questions right now. Very well written with visual reminders to help in the field. Can’t wait for the next excerpt…..

  12. Gary – I have been linked to a few of your postings and all I can say is that you have a gift at putting the crucial techniques into words with examples that everyone can grasp. I thought I might be the only one sitting around playing with my Droid while checking different Hyper Focal Distance data but you have confirmed that there is at least two of us out there. I do the exact same thing as you and try to get a good idea of where my general focus should be to achieve HF and once I gave up on the all to often simplified 1/3 idea, things have been much better. Keep up the great work. I will be checking in often.

    • Thanks, Terry. I find the more I refer to my hyperfocal app when circumstances permit, the more accurate I am at estimating hyperfocal distance when I don’t have time to check it.

  13. Pingback: Not easy, but simple « Eloquent Nature by Gary Hart

  14. Thank you very much for this. I didn’t even know that there was a DOF Preview button on my Canon T4i. O__O I will definitely keep this in mind. Great article.

  15. i have a canon 5d mk11 and a canon17-40 wide angle lens, please could someone explain the procedure on how to focus 1/3 from the bottom of the scene?

    • Gary, you’ve asked the wrong person. I don’t like the 1/3 focus technique and think it creates more problems than it solves. I’m sure if you Google it you’ll find a wealth of input, but I promise you’ll be better served brushing up on hyperfocal focusing and applying the approach I suggest in my article.

  16. I’m a travel photographer/landscape photographer – I use the 1/3rd rule a lot, along with knowing what the sweetspot (f/stop) of the lens I’m using and get tack sharp landscapes everytime. The idea that one has to use f.22 along with HFD has long since been debunked. Check your photos; corner to corner edge to edge using different f/stops to discover what the best f/stop for that lens is while using HFD; and have fun out there.

    • Thank you for your comments, Joseph. Ultimately, photography is all about results, so if your approach works for you, that’s great. I’m afraid that the 1/3 “rule” is a fallacy that just won’t die—it’s slightly better than nothing (a random focus point), and in the short-term it might benefit beginners who are inclined to automatically focus in the middle or on their primary subject. It also can help when things are happening too fast to focus properly. But the people who use it can’t even agree on what it is: Is it 1/3 of the way through the scene, or 1/3 of the way into the frame (two very different focus points which yield very different results)? Because we often print large, and there’s only one plane of absolute sharpness, most serious landscape photographers can’t afford to miss the focus point by even an inch or two. Of course if your entire scene is at infinity (the very thing my post advocates against), it really doesn’t matter where you focus. And if you never print large, you may be completely unaware of softness that doesn’t show up in smaller prints.

      Using f/22 at the hyperfocal distance has never been a consideration for serious landscape photographers because the hyperfocal distance changes with the f/stop, and no photographer who understands anything about the physics of light would use any f-stop smaller than necessary. In fact, the diffraction at f/22 makes it virtually out of the question for any image that might be printed large. (So it’s hard to debunk something that was never taken seriously in the first place.) FYI, I’ll be writing an article explaining diffraction for “Outdoor Photographer” magazine later this year.

      I think as long as you stick to calendar-size photos and don’t put a lot of stress on the front-to-back aspect of your compositions, your focus approach should serve you well. But when you attempt to add more depth to your images, your focus choice will become more critical. You can learn more about focus in landscape photography here: Depth of Field. You also might want to read my OP article on creative focus that appeared in the June 2016 “Outdoor Photographer.” Happy shooting.

  17. Thanks for the update Gary!

    “focusing closer will soften the distant scene; focusing closer will extend the area of foreground softness” … should the latter be focusing further?

    Also, what do you mean by: “Aperture is measured in f-stops, a ratio (photographers conveniently remove the numerator for ease of reference”? I always thought of aperture as the ratio of focal length and diaphragm opening. So the f# is the overall ratio, not the denominator.

    • Thanks, Miguel. Good catches—the f-stop mistake was left over from an explanation of why we see the numerator stripped from shutter speed; the “focus closer” mistake was just me being stupid.

  18. This is an excellent article: I feel as if I am finally understanding some technical language in the world of photography that I previously did not. You are not only a gifted photographer, but also a gifted teacher. I look forward to applying this knowledge!

  19. Thanks for this indepth explaination. I particularly benefited from the metaphor, hat, baseball and gun, easy to remember.
    Thank you.

What do you think?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: