Depth of Field

(This is Lesson 5 of My How It’s Done Series)

In the last lesson we discussed aperture and aperture value.  Admittedly, it wasn’t the most exciting lesson.  This lesson should be more interesting to your creative side.  We are going to talk about how aperture changes the way your pictures look.  Aperture controls depth of field.  Depth of field is how much of your photo is in sharp focus.

A photo with a large depth of field has a large area of the picture in focus.  It is sharp from front to back.  The above photo of Dream Lake in Rocky Mountain National Park has a large or deep depth of field.  Everything from the rock in the foreground to the trees and mountains in the background is in focus.  Most landscape photos have a large depth of field.

A shallow depth of field is one where only a portion of the picture is in sharp focus.  The above photo has a shallow depth of field.  I focused on the raspberry and used a wide aperture (f/2.8).  The berry is in focus and everything else in the photo fades into smooth bokeh.

Between a shallow and deep depth of field there is a lot of room for a photographer to play, and the great thing about photography is there is no right answer.  Right behind composition and lighting, depth of field is a photographer‘s most powerful creative control.  A creative photographer should have a good understanding of how aperture controls depth of  field.  With a pinch of study and a lot of practice depth of field control will become second nature.    By the end of this lesson you should understand depth of field and know how to control it to achieve the creative effects you desire.

First, we have to define depth of field.  I’m not going to give you the scientifically perfect definition.  You can check Wikipedia for that.    I’ll define depth of field in a more practical manner.  Depth of field is the distance in front of and behind your focus point where you can expect objects to remain in sharp focus.  When you focus your camera, in theory, everything in the plain of focus is in perfect, sharp focus.  Any other object that falls on the plain of focus should be in sharp focus too — as sharp as your lens is capable of producing.  The further an object is from the plain of focus the less sharp it appears in the photo.  Within a certain distance from the plain of focus objects remain reasonably sharp.  By reasonably sharp we mean you can’t tell with your naked eye that an object is any less sharp than an object that lies precisely on the plain of focus.  This area surrounding the plain of focus where objects remain “reasonably sharp” is depth of field.

I realize that last paragraph might be confusing.  That’s why I devised the above diagram.  Imagine you focus the camera on the front of the flower (see the focal point in the diagram).  The plane of focus in the diagram is represented by the vertical line that runs parallel to the camera’s image sensor.  In theory everything that touches that plain of focus would be in perfect focus.  The two vertical lines on either side of the plain of focus represent depth of field.  Any object placed between those depth of field lines would be in good focus as long as the camera stays in the same place and the point of focus isn‘t changed.

It is important to note here that the depth of field lines depicted in the diagram aren’t extremely important in real world photography.  It’s not as if focus falls apart when you reach those lines.  If there was another flower slightly outside those depth of field markers it would still be sort of in focus.  The exact placement of the edge of depth of field is calculated and one of the factors in the formula is a measure of fuzziness.  Somewhere in the history of photography all the camera engineers got together and decided just how fuzzy is too fuzzy.  The camera engineer’s fuzziness factor is part of the depth of field calculation. Your amount of acceptable fuzziness might be different from an optical engineer.  The important concept for a photographer to understand is that you can only focus at one specific distance from your camera.  The further an object is from this plain of focus the less sharp it will appear in the final photo.

The good news about depth of field is you the photographer can control it.  You get to decide how much of your picture is in focus and how much is blur.  To control the depth of field you simply change your camera’s aperture setting.  Larger aperture’s (smaller aperture value) have a smaller depth of field and smaller apertures (larger aperture value) have a bigger depth of field.  As a photographer you gain direct control over depth of field by shooting in Aperture Priority Mode or Manual Mode.  An upcoming lesson in this series is going to be titled “Aperture Priority, The King of All Modes”.  Even though I haven’t written that lesson yet, I suggest you start doing most of your shooting in Aperture priority mode so you start to get used to it.

The above diagram doesn’t require too much explanation.  I wanted to illustrate that changing apertures changes Depth of field.  Watch the animation a few times.  It’s hypnotic.  Mediatate on this thought as my animation lulls you into a state of nirvana, “Bigger f stop equals bigger depth of field.  Smaller f stop equals smaller depth of field.”

By now you should have a pretty good idea about what depth of field is and how you can change it.  If you are a good student you should have a question or two brewing in your brain.  You are probably wondering how much depth of field do I need?  What aperture do I set to take a picture of my dog?  What aperture works when photographing a flower?  How about my trip to the Grand Tetons?  The answer to those questions is there is no exact answer.  Seldom will you ever find yourself in a scenario where depth of field will be your only consideration when you decide how to set your aperture.  However, it’s good to have a ballpark idea of which aperture is best for a given situation.  Since this series is based towards beginners I am going to give you a list of aperture values and then give some examples of when you would use them.  This is far from a comprehensive list and I am sure a different photographer might give you different examples and would probably disagree with some of these suggestions.  As a beginner you have to start somewhere so here is my aperture value list:

f/2.8 — This aperture gives a very narrow depth of field.  It works great for isolating a subject against a blurry background.    For an example look at the photo of the raspberry from earlier in this article.  F/2.8 is also a useful aperture when photographing in low light situations.  The large aperture opening allows more light into the camera and allows a faster shutter speed.  A lot of times f/2.8 is used out of necessity because of lighting rather than because it is optimum for depth of field.  We’ll discuss the aperture shutter speed relationship more in a later lesson

f/5.6 — If you’re shooting portraits of a single person this  is the go to f-stop for most photographers.  When shooting at 5.6 if you focus on a person’s eyes, you will have enough depth of field to keep the subject’s entire face in focus.  Objects behind or in front of your human subject will be slightly out of focus.  This focus effect helps keep the person in the portrait the primary subject by softly blurring objects in the background or foreground.

The above photo is an f/5.6 portrait of my niece taken on the 4th of July.  In the background there is a shower of sparks bursting out from some fireworks.  Had I used a higher f-stop for this photo the fireworks would have competed for attention from the primary subject, my niece.  With the shallow depth of field created by using f/5.6 the sparks turn into an interesting background but don’t confuse the viewers eye with too much information.

f/8.0 — This is the Swiss Army Knife of f-stops.  When I am turn off my camera, I always am sure to leave it set to f/8.0.  With my camera at f/8.0 I’m ready for anything.  When that million dollar photo opportunity comes my way, my camera will already be set to the magical f/8.0.  Why f/8.0?  Because f/8.0 is a great compromise that works OK for most situations.  This aperture gives a pretty decent depth of field and also isn’t so small as to cause a slow shutter speed.  If while rounding a bend in a trail you stumble across Elvis riding a unicorn, f/8.0 could get the shot. Most everything in the frame would be in decent  focus and your shutter speed will be high enough that you can handhold the camera.  Remember this old photo journalist’s saying, “f/8.0 and be there.”

f/16 — This is my landscape setting.  I use f/16 when I want to get a lot of things in focus.  The trouble with f/16 is it is a very small aperture and not much light is exposing the sensor.  That means slow shutter speeds.  Unless it’s midday sun shooting at f/16 requires a tripod.  You might be asking yourself,” if f/16 is good for landscapes wouldn’t f/22 be even better?  After all, f/22 would give you greater depth of field than f/16″.  That logic is partially true.  F/22 would give a greater depth of field than f/16.  However, there is a catch.  At extremely high f-stops most lenses start to have a deterioration in sharpness.  It’s and engineering issue and every lens is different.  If you find that you shoot a lot of landscapes or subjects that require small apertures you might want to experiment with your lens.  Play around with different high aperture settings and see where you notice some deterioration in image quality.

Ok, so that’s my controversial f-stop list.  Remember, those aren’t hard rules to follow.  It’s just guidance for the beginner photographer.  In coming lessons we’re going to discuss the aperture/shutter speed relationship and you’ll learn that every depth of field decision involves compromise.  With time and practice you’ll develop your own style and decision making process when it comes to choosing an aperture setting.

There is one more subject we have to cover before completing this discussion on depth of field.  It is important for a photographer to understand that depth of field changes as the point of focus moves closer or further from the camera.  If you focus really close to your camera depth of field is very narrow.  When you focus on something that is far away from your camera depth of field is deep.  For example, imagine you are standing outside a fenced pasture and you’re taking a photograph of a horse that’s standing about 20 yards away.  With your aperture set to f/8.0 chances are that the entire horse will fall inside of the depth of field and the horse’s entire body will remain in sharp focus.  Now, imagine that the horse walks over to take a closer look at you.  With the horse standing two feet in front of your lens, f/8.0 is no longer enough to keep the entire horse in focus.    With the horse this close f/8.0 might not even be enough to keep its entire head in focus.  How many close up animal portraits have you seen where the subject’s eyes are in focus, but the tip of its nose is blurry?   That effect is a result of the shallow depth of field created by the subject being so close to the camera.  Similarly, successful closeup macro photos of bugs and flowers often require very high aperture settings.  To keep the length of a grasshopper in focus might require an aperture of f/16.0 or higher depending on how close the grasshopper is to your camera.

On the flip side, if you focus your camera on something that is far away depth of field is extremely deep.   Imagine that you are taking a photo of a city skyline for a few miles away.  When you focus on the distant skyscrapers your depth of field will stretch from halfway between you and the skyscrapers all the way out to infinity.  That’s pretty far!  Anything that falls within that range would be rendered in sharp focus in the photo.

To help drive home the point that depth of field shrinks as the subject moves closer to the camera I created the above animation.  Like the previous diagrams in this lesson I drew one line that represents the plain of focus and the the two other two lines represent the depth of field.  Watch how the depth of field shrinks as the vicious bunny charges toward the camera.  In the first frame f/8.0 is enough to keep the entire rabbit in focus.  By the last frame only the front of the rabbit’s head is in focus.

We have finally reached the end of this lesson.  By now you should have a pretty good understanding of depth of field.  It’s time for you to take out your camera and do some experiments with depth of field.  Try all sorts of different apertures.  Focus on subjects close to the camera and then focus on things that are far away.  Through practice you will learn how to use depth of field creatively in your photos.

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