Photo Fundamentals: Depth of Field

Unbeknownst to many first time DSLR buyers, the ability to achieve shallow Depth of Field is actually one of the main reasons to buy a DSLR camera... These days its a sad reality that most people don't make prints much bigger than 8x10, if they make prints at all. So all of the nonsense about megapixels and lens sharpness can really be thrown out the window for most amateurs. However the ability to achieve shallow depth of field is something that cell phones and point and shoot cameras cannot achieve.  Photography has always been more about knowing how to use the equipment. I guess you could apply this to many crafts/professions, but it seems that every new photographer thinks a "better camera" will help them take better pictures. For 95% of people out there, this couldn't be any farther from the truth. The lighting, the lens, and most importantly the Loser (yeah come on if you're walking around with a DSLR with a giant lens, you're a loser just like me haha) using the camera the three key factors. I am obviously not the most technical product reviewer out there, but sometimes I use lingo that the casual shooter may not understand completely. That is why I am going to dedicate several of my upcoming blog posts to "Photo Fundamentals." If you already consider yourself an expert, I would keep reading anyway, most of these posts are going to be brief and you can never get enough re-enforcement.  Maybe you know something that I don't and you can add to the conversation.  So here is my first "Photo Fundamentals" post on Depth of Field. (Click MORE)

You've probably heard the term thrown around by other photographers or worse, on an internet forum full of bickering hobbyists.   So, what is depth of field?  According to Wikipedia, "Depth of Field is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image."  Basically its everything that appears to be "in focus" in a photograph.  There is a common misconception that when you stop down your lens to a smaller aperture, you are making things "more in focus"  This isn't the case as a lens can only focus in one spot.  So in reality, even at f/16 or f/22, only one point in your photograph is truly "in focus" and the rest simply appears to be.  So basically when someone comments on the Depth of Field in a photograph, they are referring to how sharp parts of a photograph appear to be outside of the "plane of critical focus" If you've read this far and still aren't getting it, keep reading.  You don't need to understand all the minutia of the math and technical terms behind Depth of Field in order to take good photographs.  If you've read this far and feel like Einstein in a Pre-School class, I suggest checking out this very extensive article on Depth of Field.  There is also a depth of field calculator on this site as well.

Here are the three absolute factors that determine how much Depth of Field a photograph has:

1. Aperture - The aperture you select when taking a photograph will not only determine how much light is let in through the iris of the lens, but it also directly impacts how much depth of field your photograph will have.  It is  the easiest and most effective ways to do just that.  Wider apertures (think f/1.2, f/1.4, f/2, and f/2.8) let in more light and provide for SHALLOW depth of field in a photograph.  This means that anything behind or in front of your subject (that you focused on) will appear to be very blurred.  This is particularly effective in portrait photograph as more attention is brought to your subject, rather than the surroundings.  Smaller apertures such as f/11, f/16, f/22, and f/32 will provide for MORE depth of field in a photograph, meaning that more areas in front of and behind your subject will appear to be in focus.  When photographing landscapes, you probably want to have more depth of field, so stopping down your lens is a good idea.  Some older and more professional lenses have a depth of field scale on the lens that will help you determine what aperture to use.  Here is a good article on how to use a depth of field scale.  With a little practice you should be able to master applying the use of different apertures for both how much light is being let into your camera and how much Depth of Field you want in your photograph.

WARNING: Stopping down a lens ALL the way will cause a decrease in image quality due to an optical phenomenon called "diffraction."  While we want our landscape photographs to be sharp from corner to corner, it sometimes works against you to keep stopping down, yet at other times you will need to in order to give everything in your shot the appearance of being in focus.  Depending on how far you are from the subject in your photograph (see bellow), f/11 or f/16 will usually give plenty of depth of field for landscapes which are typically shot with wide-angle lenses (another factor).  Think about it this way, once you've reached the "ideal" aperture for your landscape image, stopping down further will no longer yield positive results, it will only decrease image quality.

2. Focal Length - The lens you are using will make a major impact on how much Depth of Field your final image has.  Wide angle lenses will allow you to achieve more depth of field in your images.  Think about it, have you ever seen a fisheye photograph that has shallow depth of field? This works out nicely because wide angle lenses are the best for most landscape shots. For example you should have no problem getting plenty of depth of field in an image with a 10-24mm lens (on a DX camera) at around f/11 or f/16.  In only the most bizarre situations would you need to stop down any further to give your scene the appearance of total edge to edge sharpness.  Resulting images will have LESS Depth of Field when using a lens with a longer focal length.  That is why you see both portrait and sports photographers lugging around big lenses, believe it or not, they aren't just compensating for something else!  The combination of shallow depth of field and the compression of space that are the result of using telephoto lenses works out perfectly for photographers who want to "Separate" their subjects from backgrounds.  This all sounds very easy and it is.  The tricky part is when you want to use a telephoto lens for a landscape shot or a wide angle lens for an image that you want LESS Depth of Field in.

3. Distance to Subject - How close you are to your subject will also impact the Depth of Field in your photograph.  Stand further away for MORE Depth of Field or get all creepy and close up for LESS Depth of Field.  While this may not make sense to you at first, there is no better proof than trying it for yourself.  Set your aperture and focal length (better yet use a fixed length lens and not a zoom) to a set value.  For the sake of this example let's just say it's 85mm at f/4.  Pick out a point to focus on and take a picture.  Now without changing any of your camera's settings take ten steps forward and focus on the exact same point.  Finally, take twenty steps backwards and repeat the process.  You should be able to see a major difference in the resulting Depth of Field, especially when viewed on a computer monitor and not the back of your camera.

So what does this all mean?

Being able to manipulate the backgrounds and foregrounds of your photographs is a very powerful tool.  There is no rule that says every landscape has to have large depth of field or that every portrait has to have the shallowest possible amount of depth of field.  Just like your gear, depth of field is a tool that you can learn to use casually or master, depending on how important it is to your images.  Advanced landscape photographers will sometimes use depth of field calculators to determine "hyperfocal" distance.  In layman's terms that basically means what distance they should set the lens to (manually) in order to achieve the highest degree of depth of field without having to stop their lenses down as far.  (Remember stopping down too far reduces resolution). There is more you can do with Depth of Field using a Tilt-Shift (Canon) or Perspective Control (Nikon) lens.  Let's see some of your photos that you've achieved great or shallow depth of field with.  Feel free to send them to me [email protected] and I'll post them here on the blog!

-MZ