How to Determine a Range of Focus in Photography

Instructions

• 1

  Measure the amount of available light. The brightness of your subject will indicate what aperture and shutter speed to select for a proper exposure. A helpful rule to abide by is the Sunny 16: when you are shooting an average subject in bright sunlight, your selected aperture will be f/16 and your shutter speed 1 over the selected ISO (film or camera sensor's sensitivity to light). For example, shooting on a bright sunny day with ISO 100 film would require an aperture of f/16 and a shutter speed of 1/125 sec. for proper exposure. This rule should be used for reference purposes as you will adjust your aperture and shutter speed based on the desired depth of field and, ultimately, range of focus.

• 2

  Set your aperture. If you are using a manual focus lens for an older SLR camera, do this by turning the aperture ring (located near the mount or at the front of the lens) to the desired f-stop number. Depending on the type of lens you're using, common f-stops can range from f/1.2 to f/22 or above. Larger apertures (f/1.2 to f/5.6) have a shallow depth of field, meaning that the distance of their effective focus is short. The focusing point will be sharp and detailed while the rest of the image is blurred and out of focus. Smaller apertures (f/11 to f/22) have a larger depth of field, meaning that the distance of their effective focus is much longer. The focusing point as well as the rest of the frame will be sharp and in focus.

• 3

  Set your shutter speed. If you are using an older SLR body, this can usually be done by turning an adjustment knob on top of the camera. The camera's shutter speed must correlate with the selected aperture in order to produce proper exposure. For example, say you are shooting on a bright sunny day with ISO 100 film but want to emphasize your subject by reducing the depth of field. If you stop-down f/16 to f/5.6 (four stops), you must stop-up your shutter speed of 1/125 to 1/1000 (four stops) to ensure proper exposure.

• 4

  Focus your lens accordingly. All lenses feature two adjustable rings, one for aperture and the other for focusing distance. If you have chosen a large aperture (f/2.8, for example) to shoot a close portrait or to blur a scene's background, your range of focus will be relatively short. If you have chosen a small aperture (f/16, for example) to shoot a distant landscape or to sharpen an entire scene, your range of focus will be much longer.