Tuesday, August 1, 2006
Mastering The Wide-Angle
Exploring with the wide end of the focal spectrum opens up a world of creative compositional possibilities
Such tiny apertures provide tremendous depth of field, but they also do something else: diffract the light waves (bend the waves around the edges of the tiny diaphragm opening) severely, which reduces fine detail. Diffraction is why those tiny lenses in consumer digital cameras rarely stop down beyond ƒ/8. It's also why you should stop a wide-angle lens all the way down only when maximum depth of field is essential to a shot; don't arbitrarily shoot everything at the lens' minimum aperture figuring that will produce the sharpest image: it won't.
See how it works with your wide—angle lens. Mount the camera on a tripod, focus carefully on a subject five feet away and shoot images at all the lens' apertures (adjusting the shutter speed accordingly to maintain correct exposure, of course). Then carefully focus on a subject 10 feet away and repeat the sequence. Examine the resulting slides, negatives or prints with a loupe or at 100% on screen for digital images. This will give you a good idea of how your lens performs at different apertures (and how clean your D-SLR's image sensor is; stopping a wide-angle lens all the way down brings any dust spots on the sensor into sharper focus, making them much more evident in photos).Focusing Considerations
Because the subject is generally smaller and there's more depth of field, it's harder to tell when the viewfinder image is at its sharpest when focusing a wide-angle lens manually. When autofocusing, make sure the active AF target is over the subject you want focused—it's easier to "miss" with a wide-angle's wider angle of view. It doesn't hurt to check the minimum focusing distance when comparing lenses because a longer minimum focusing distance limits your ability to maximize the wide-angle "distortion" effect—you can't move as close to the subject.
Minimum focusing distance refers to the distance from the subject to the focal plane (film plane or image sensor) when the lens is focused as close as it can focus. Minimum object distance is the distance from the subject to the front of the lens when the lens is focused as close as it can focus. Obviously, minimum object distance will be shorter than minimum focusing distance, something to keep in mind when comparing lens specs.
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