How To Understand Your Camera – 3
by William Lulow
Now that you know a little about a digital sensor’s sensitivity to light, let’s turn to the next part of your camera, the lens opening or APERTURE.
When the lens is attached to the camera body, it will be recognized by the camera through electrical connections. Depending on the lens, the camera will know what the largest and smallest lens openings are.
Large lens openings do the following:
- Let more light into the camera
- Give very shallow “depth-of-field” to the images
- Make the image softer in appearance
- Allow you to shoot in low light situations
Small lens openings do the following:
- Let less light into the camera
- Give greater “depth-of-field” to the images
- Make the image sharper in appearance
- Allow you to shoot in very bright light situations
Most lenses do not perform at their best either wide open or at their minimum aperture. For best results, try to shoot with the lens stopped down one or two stops from wide open and one or two stops open from its minimum opening as well.
DEPTH- OF- FIELD
Depth-of-field refers to the parts of the image that are in focus. A large lens opening will yield very short depth-of-field ranges. This means that when you focus a lens that is open to f/2.8 for example, the only thing that will be in focus is the object on which you are focused. The background and the foreground will be out of focus. This can be used creatively to draw the viewer’s attention to just what you’ve focused on, or to make the background appear soft in order to separate the main subject from it.
The rule is, the wider the lens opening, the shorter the depth-of-field. Conversely, the smaller the lens opening, the greater the depth-of-field. Great depth-of-field ranges can be achieved with wide angle lenses. They will focus on most of the scene and render the elements all sharp. They can do this because they expand the rendering of a scene, and thus have the ability to show greater depth-of-field.
Short depth-of-field ranges can be achieved with telephoto lenses. Because of their ability to magnify and compress distant objects, they have limited ability to render an entire scene in focus. This is also due to a telephoto lens’ limited field of view.
Here is a DEPTH-OF-FIELD scale that you might find on a typical lens:
These scales are read as follows: If you look at the f/22 numbers, you will note that they are the widest apart. This means that everything in the scene from about 15 feet from the lens to infinity will be in focus. If you look at the f/4 numbers, you will note that everything from about 7 feet from the lens to 10 feet from the lens will be in focus. The bottom numbers indicate f/stops, the blue numbers indicate distance in FEET. This gives you a pretty good idea what will be in focus at the f/stops indicated. The diamond in the middle is a measurement of what the lens is focused on currently.
Also, most modern, digital cameras are designed to open a lens to its maximum aperture so that the user can focus with the most amount of light while they are composing an image. They also have what is called a “Depth-of-field” preview button. This device will stop down the lens to the aperture that it is set for to give the user an idea of what the scene will look like at the selected f/stop. If you use this tool carefully, you will get a pretty good idea of what will be in focus. It is a good idea to learn where your camera’s DEPTH-OF-FIELD preview button is and make use of it.
Depth-of-field can be used creatively in photographs. There are times you may want the background to be out of focus so that the viewer’s attention is directed at the subject. There are times when you will want the whole scene to be in focus so that all the details can be seen clearly. How and when to make use of these tools is most often a matter of personal taste, but keep in mind that in any photograph, the details that are meant to be sharp, should be sharp.
The next article will talk more about shutter speeds.