Proper focus on a prime lens will give you tack-sharp photographic results.
A prime lens is any fixed focal length lens (for example, a 50mm is one of the most popular prime lenses). Prime lenses do not have the ability to zoom, so the photographer must move closer to or farther from their subject to achieve desired composition within the viewfinder's frame. Most lenses come equipped with a distance scale that allows the photographer to zone focus (judge appropriate focus based on estimated distance from the subject).
Instructions
Focusing Through the Viewfinder
1. Look through the camera's viewfinder window. Ensure that the lens is attached securely to the mount at the front of the camera.
2. Point the camera toward your intended subject. Rotate the focus ring (located near the rear element of the lens, in front of the mounting threads) clockwise for far away subjects and counterclockwise for closer subjects. Fine tune your image by choosing a well-lit detail on which to focus.
3. Adjust your aperture (size of lens diaphragm opening) to achieve the desired depth of field (DOF). DOF refers to the range of effective focus in an image, or how much of the image can remain in focus at the aperture and shutter speed you have chosen. For example, if the foreground of an image is sharply focused and the background is blurred, it can be said to have a shallow DOF. If the foreground and background of an image are both sharply focused, it can be said to have a large DOF. Aperture ranges from f/1.7 to 5.6 will often provide shallow DOF, while f/8 to f/22 will provide larger DOF.
4. Set your shutter speed in relation to your aperture to achieve proper exposure. As a general rule, larger f-stops (f/2.8, for example) will require a faster shutter speed, as the diaphragm is almost wide open at this stop. Smaller f-stops (f/16) will require a slower shutter speed, as the diaphragm is nearly closed at this stop.
Focusing Using the Distance Scale
5. Pre-set your aperture and shutter speed settings. As a general rule, on a sunny day an aperture of f/16 and a shutter speed of 1 over your ISO rating (or ISO sensitivity for digital cameras) will provide proper exposure. Increase the aperture as daylight dwindles or weather becomes inclement (for example, f/5.6 with same shutter speed when overcast).
6. Estimate the distance, in either feet or meters, between the camera lens and your subject. Locate the distance scale near the top rear element of the lens. It is an arrangement of lines with the smallest f-stop (f/16 or f/22) on either end and a midpoint, usually a red line or arrow.
7. Turn the focusing ring so that the distance you have estimated is within the range of your selected aperture. For example, if your subject is seven feet away and you have selected f/8 as your aperture, rotate the focus ring until seven feet is between the lines labeled "8" on the distance scale. At f/8, your subject and anything two to three feet in front of or behind it will be in focus.
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