What is Depth of Field - Beginning Photography BasicsWriten by Chip Clark
At some point all beginning photographers are confronted with certain technical aspects of photography that have them either burning up rolls of film, or loading up memory cards! Two in particular: Exposure (which will be addressed in a different article) and Depth of Field (or DOF) leave the newly shutterbug bitten novice shaking their head, wondering what they are doing wrong.
When I first started taking on an informal teaching role with beginning photographers it was interesting that the single most common question asked by them was: How do I make the background blurry and my subject sharp? and of course, what do I need to do when I want everything in focus?
It's inevitable. If you desire to take your photography to a higher level of quality, you will need to understand what causes short and long depths of field, and especially how to manipulate it to express your vision. Let's get started...
First - what is a photograph with a short Depth of Field, and what is one with a long DOF? Quite simply, a photograph with only the subject in focus, and everything before and behind it blurry, is a photograph with a short DOF. An image with everything in the foreground to the background sharp and in focus has a long DOF. With this highly sophisticated formula I'm sure you can figure out what a medium DOF is!
Why use a short DOF? When you reach this level of being able to control exactly what you want in focus (typically referred to as Selective Focus) in your photograph you will have developed a dynamic tool that will create powerful photographs! You will see this used extensively in photojournalism - such as the photographer focusing on one particular individual in a crowd of people. Creative use of this tool certainly gives sustenance to the term: A picture paints a thousand words!
Quite often you will see the use of a short DOF in glamour portraiture. A classic example is when you see the model's eye closest to the lens sharply focused, and the one furthest is blurred. It's one of the most unique techniques a photographer can utilize to convey her or his message.
What about a long DOF? Landscape photography is the best example of the long Depth of Field in use. Shooting images of seemingly endless vistas would render a photograph worthless if only a small portion of the 'field' was in focus. Since you want virtually everything from closest to farthest tack sharp - you will want to shoot with a long DOF. You can see this utilized with incredible results in the works of the greatest fine art photographers such as Ansel Adams and Edward Weston. But even when making photographs of spectacular scenes, there will be times when your creative vision will want to focus attention on a tiny, fragile flower amidst nature's grandest formations. Developing these techniques will arm you with that kind of photographic versatility.
So now that you understand what DOF is, how do you make it work? This is where we begin to get a bit technical, but it's important you understand it. Since DOF will vary depending on the focal length lens you are using, my examples will be in regards to using a normal SLR lens in the 45mm - 70mm range. To be able to manipulate DOF you must be able to adjust the aperture (or F-stops) on your camera. Most all SLR cameras that are even remotely modern can do this by switching your mode to Aperture Priority mode - or AV mode.
While I will not give a detailed explanation about aperture in this article - the simplest way to understand is this: An F-stop is the adjustable opening that controls how much light coming through your lens hits the film or digital sensor. The shutter speed is involved with this as well, but for now let's stick with aperture. The F-stop also controls the DOF of an image.
Older SLR camera lenses typically have the F-stop numbers on the lens barrel. An older very basic lens may have numbers around the aperture ring like: 2.8 - 5.6 - 8 - 11 - 16 - 22. These are the F-stops, or the aperture opening settings.
More modern cameras are electronic and the F-stops are usually seen at the bottom of the viewfinder. Contemporary lenses usually have more F-stop settings available, such as: 2.8 - 3.5 - 5.6 - 6.3 - 7.1 - 8 - and so forth, possibly all the way up to 32.
To choose the DOF you wish to use for a particular shot you need to understand this very basic concept: The lower the F-stop number - such as 2.8, the shorter your DOF will be. The higher the F-stop number - 22, the longer the depth of field. To simplify it further - making a photograph with F22 or higher is going to have everything in the final image in focus. Shooting with the aperture set at 2.8 is going to mean that only what you specifically focused on is going to sharp.
Take a moment to absorb this because this basic concept is the nuts and bolts of creating a quality photograph, rather than just taking a picture. The very best exercise you can do to practice this technique is to line up 3 objects - such as apples. Place them on a table about 2' apart lined up going away from you at just enough of an angle so the first one isn't blocking the other two. Place your camera about 3' from the first one, and focus on the apple in the middle. Shoot several shots - each one at a different f-stop, starting with the lowest number (short DOF) and changing to the next higher f-stop after each shot...all the way to the highest F-stop.
If your lens has an F-stop number as low as 2.8 you will see that maybe only the forward surface of the apple is in focus - everything from closest to furthest is gradually very blurry. With each shot changed to a higher F-stop number you will see more of the field in focus. By the time you get to the highest F-stop setting, virtually everything in the photo will be sharp and focused.
Most SLR cameras have a DOF Preview Button. If you use it while looking through the lens at your scene - you will see what the final image will look like. Only problem is - the higher the F-stop number is, the smaller the amount of light is let in. So it can be very difficult to see because it will be very dark. After practicing with these techniques you will not bother with the DOF preview button. You will know how the image will be reproduced.
That is the mystery of Depth of Field in a nutshell! Yes, there is more in-depth aspects of DOF - such as understanding Hyper Focal Distance, and of course knowing that you will get different DOF results with longer and shorter focal length lenses. But understanding these basic DOF concepts will revolutionize your photography, and give you one more step up in photographic quality.
Chip Clark is a San Diego based professional photographer, with over 20 years experience in landscape photography, wildlife photography, sports photography, and portraiture.
Chip Clark's photography tutorials are available at http://www.chipclarkphotography.com/advanced-techniques-for-beginning-photographers-PL.htm
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