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Auto Focus - Manual Focus |
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Auto Focus With modern digital cameras we have the option of using Auto Focus and Manual Focus. Most of the time Auto Focus will get us well within the ballpark of pin sharp focus, but there are times when it will not perform well. Auto Focus is best used when we have lots of available light and contrasting subjects. If we have low light, and average contrast, and a flash attachment installed the flash may emit several bursts of light while the Auto Focus is setting focus. This is also used for Flash with "Red Eye Removal turned on. Manual Focus allows us to set the focus point anywhere we want to achieve a desired effect. The Auto Focus switch on the lens must be turned off while adjusting focus. Failure to turn off Auto Focus will allow the camera to set focus as we depress the shutter button half way down; adjusting the focus ring will allow manual focus, but when we press the shutter button all the way down Auto Focus will engage and the exposure capture will be delayed until Auto Focus is completed.. In modern digital cameras Auto Focus is measured with differences of contrast surrounding the focal point in the viewfinder. Most of the time Auto Focus will capture the image in good usable focus, however, it may be necessary to manually adjust the focus to gain sharp focus within the range of the Hyper Focal Distance. |
Manual Focus Manual focus is adjusted by turning the focusing ring on the lens barrel and viewing the principle subject through the viewfinder, or LCD display panel on the back of the camera. Auto Focus must be turned off to prevent stripping the gears of the auto focus mechanism. A focusing aid borrowed from the 35mm film days is a replaceable focus screen. This screen replaces the original focusing screen that came shipped with the camera. The original screen was mostly a ground glass screen with cross hairs centered in the field of view. The replacement screen is mostly ground glass with 9 rectangular blocks etched into the screen for easier alignment of vertical and horizontal objects.  In the center of the screen is a split image refractive circle, and when the point of focus is viewed through the circle the image will split into two halves, as focus is optimized the split image will merge together into one finely focused element. If you also change the Aperture values you will change the DOF and HFD from the principle subject to the camera. By using the split image focusing screen you can adjust the Aperture and HFD range to bring all important elements of the scene into sharp focus. The split image screen will allow you to change the view of your subject to insure all elements are in acceptable focus. |
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