Tuesday, December 2, 2008
Close And Personal
Close-Up Sharpness • Water, Sky And Time • Blue Sky Blues • Fine-Art Prints
Q Is there a fundamental problem with using close-up filters on zoom lenses? I’m getting good results with a set of Quantaray close-up filters on my 28-75mm lens at all focal lengths, but my 80-200mm lens only provides a crisp image at 80mm. It doesn’t seem to make a difference if I attach the close-up filter directly to the lens or on top of the skylight filter. Stacking the filters to get closer just made the image problems worse.
Via the Internet
A Close-up lenses, when attached to the front of your prime lens, essentially convert the lens to a macro-capable optic, improving close-focusing ability. Their advantage is that they’re smaller in size and less expensive than a prime macro lens. Single-element close-up lenses (diopters) such as you described are designed for use on lenses in midrange focal lengths (35-80mm). They give reasonable results in the center of the image, but generally lose their sharpness at the edges due to their simple optic design. They won’t give good results on your zoom telephoto, as you’ve discovered. Mid-range telephotos require a highly corrected two-element close-up lens such as the Nikon 6T (62mm) or the Canon 500D (77mm), which can be adapted to lenses with smaller filter diameters. Canon also makes a 58mm two-element close-up diopter (the 250D) for use on 38-135mm lenses.
An interesting capability of a close-up diopter/zoom lens combination is that you can maintain the same working distance while changing the magnification of the subject simply by zooming the lens. But be careful about stacking lenses and filters, as each layer has the potential to degrade your image. I would remove the “skylight” or protective filter before attaching a close-up lens.
Water, Sky And Time
Q I attempted to photograph a waterfall and give it a flowing effect. I set the camera to shutter priority mode and captured the image at ƒ/22 for one second at ISO 100. The result was silky water and overexposed sky and highlight areas. Reducing the exposure to ½ sec. solved the overexposure, but didn’t give me the look I wanted on the water. How can I have both?
A There are no graduated neutral-density filters that will solve the problem of contrast in a scene with highly variegated light and dark areas. The solution lies in the technique of High Dynamic Range (HDR), which is available in Photoshop CS2 through CS4 and with stand-alone programs such as Photomatix (www.hdrsoft.com). These programs solve contrast issues by compositing several captures of the same scene (tripod!) taken in one- to two-stop increments. The resulting processed image magically (to use a technical term) combines all the properly exposed information from the brightest sky to the darkest shadow. You generate an image with a tonal range that isn’t possible to achieve with a single—or even dual—capture. When photographed this way, the water looks even more active than it would in a single exposure because the composite includes captures of the water taken in a variety of positions over time. It’s great for the water to move, but you probably won’t like your results if wind is moving other features in the image, such as clouds, branches and grasses.
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