Staying in our Depth (of Field, that is)
Bring home memorable photographs from any vacation is fun for the family. Bringing home a memorable photograph from a vacation is what a good photographer wants.
No matter what level you are as a photographer understanding Depth of Field can make a big difference in the quality of your final prints.
Photographers utilize the optical ability of depth of field to increase, or decrease, the amount of distance that remains in sharp focus. Paying attention to a few details can defiantly make a difference.
Why Vary the Depth of Field
You might question why would you not want everything in sharp focus? You can do this if you want, but consider what, or who, you are photographing. The objective is to bring attention to the main subject of the photograph.
When we focus the lens of a camera we are using an object or subject as our primary interest. As a photographer you will decide how much more of the image in the frame should remain sharp. The more sharp a particular subject is will place more importance on the subject of the photograph.
Standing on a trail or in a grove of trees with a great mountain before you just screams for everything to be as sharp as possible. In this case, everything that can be seen is your subject matter.
Now put a person fifteen feet in front of you and they become your primary subject matter. Everything else that is still in the scene, no matter what it is, is secondary. Nothing else needs to be, or should be, as sharp as you can make that person.
Improving Our Focus
If you use a fixed lens camera with few, if any adjustments, there is not too much to do. Most of the modern digital cameras do offer standard adjustments as to a choice of scenery or people, action or portrait. Use them! They will provide some adjustment to the camera so it knows what the important subject or object is to you.
A Single Lens Reflex (SLR) camera with interchangeable lenses will always offer you the ability to select a seemingly infinite series of adjustments that will affect your photograph. Setting the f stop (lens opening) and the associated shutter speed is what will provide you with the depth of field that you will want.
Shutter speeds are always expressed in a fraction of a second. The amount that the lens is opened is stated as an f stop and usually denoted in numbers such as f2.8, f5.6, f8, f11 or f16. The smaller the number, the larger the lens is open.
The f Stop Rules
There is a relationship between the f stop and the depth of field. There is also a relationship between the selected lens opening and the shutter speed. The basic rules of Depth of Field are:
- As the f stop number increases (the lens opening decreases) the depth of field (the area of the scene that remains sharp) will increase.
- As the lens opening decreases less light is permitted to enter so to compensate the shutter speed must decrease so it stays open longer.
- The opposite occurs as you decrease the f stop number. The depth of field (how much is in absolute focus in front of and behind the subject you focused on) will decrease.
- With a wider lens opening, the shutter again compensates by increasing speed.
The Camera Adjustments
In my day one used a light meter and then selected both the lens opening and the appropriate shutter speed. Most modern digital SLR's have multiple settings that simplify this somewhat. These are either "Fully Automatic", "Aperture Priority" or "Shutter Priority" settings.
Full Automatic
In a fully auto setting the camera will make a decision on both aperture and speed depending on the available light that the internal meter sees, how you focus and other factors. This will provide you with an "average" photograph.
There is nothing wrong with this. I too will choose this setting for those places that I am just taking snapshots. When I get serious about a photograph I shift modes and select the aperture or speed settings that I want for myself.
Aperture Priority
This will allow you to set the f stop and the camera will then adjust for the necessary shutter speed depending on the light it sees through the lens. As you increase the F stop number, you increase the depth of field on both sides of the subject you focused on (toward the camera and away from the subject). The opposite is true if you decrease the number.
Shutter Priority
With this setting you are selecting the shutter speed. Perhaps some activity or action is going on that you want to capture. To do this you increase the shutter speed to help capture the moment without blurring the picture. The camera will then increase the lens opening (reduce the f stop number) also reducing your depth of field. This is perfectly OK and is how you capture the activity.
But remember, to get a good photograph of any thing that is moving you need to pay close attention and be sure that you keep your subject in sharp focus.
A Helpful Hint
As your shutter speed drops the increased likelihood of blurry photos occurs. It is extremely difficult to get a high quality hand held photograph with any shutter speed below 1/60th of a second. Use a tripod for low light or a really high f stop with slow shutter speeds.
A trick I use when I don't have a tripod with me is to brace my camera body on a tree, or anything that is steady, and hold it firmly.
See How It Works For You:
If you are serious about learning how to use depth of field and also learn how your own camera and lens affect it then do the following:
- Place a measuring tape on a table top the entire distance of the table.
- Mount your camera on a tripod so the camera position will not change. Place it so most all of the measuring tape is in the field of view.
- Focus on a number somewhat in the center of the tape. Be as sharp as you can.
- Take a series of photos beginning with either the largest or the smallest f stop and proceed, up or down, through each of them.
When you print these pictures you will notice the following:
- The number you focused on is always sharp.
- The lighting is the same in all of them because the shutter compensated automatically.
- As you scan up and down the numbers they change in softness as they get farther away from the one you focused on. This occurs more and more as the f stop number decreases and the lens opening became greater.
Study The Masters
If we study the magnificent photographs of the great wilderness master, Ansel Adams, everything in his prints is in absolute sharpness. However, he did more than great outdoor scenes. There are both people and close-up studies in his vast body of work.
I once heard a photography student state that all Ansel did was set his enormous View Camera's lens on f22 and took the picture. This guy must be either selling cheap wedding photography or flipping burgers somewhere. This person never studied Ansel's body of work nor did he read any of his books. Ansel explains how he did everything in his writings.
A great deal to photography is best learned by reading and then by doing. I am an old film photographer now converting to digital. Most everything I once learned still applies. However, there are some differences. As a result I too am back "in the hunt" to learn the techniques that work best in this new medium. As I do, I will share them with you.