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Digital photographers contantly struggle with pattern moiré
and aliasing caused by the interference between repeating patterns in the
subject (such as tweed or denim fabrics) and the receptors on the CCD used to
capture the image.
Originally developed to eliminate the scan lines when photographing TV screens, we have modified these optical filters for use by digital photographers, to eliminate moiré. They are also effective in eliminating aliasing ("Christmas Tree light" effect) caused by improper interpolation by the software of the data from the different color receptors. The filters are far more effective and rugged than the fragile (and exceedingly expensive) dichroic filters offered by some manufacturers.
Since they are used in front of the lens when making the shot, they eliminate the problem at the source, so there is no need for electronic re-touching. They are particularly useful for SLR cameras used to capture video, such as the Canon 5D and 7D. Moiré is more of an issue for video, since the camera captures the image at a lower resolution than still shots.
The filters diffuse the original to eliminate the interference pattern (moiré) created between the CCD array and regular, repeating patterns. Since they are optical filters, rather than soft focus, the image itegrity and sharpness is maintained. They are color and density neutral, so there is no color shift or change in exposure required.
Eight filters are available, designated as follows: 1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0 and 11.0. The higher the number filters provide greater sharpness at the cost of less elimination of moiré. The numbers do not correspond to f-stops, but rather to the diameter of the pattern of circles that make the filters work.
The filters are available in three configurations:
1. 2.5 inch diameter round filters mounted in Series 8 (67mm) threaded filter rings for $130. In many cases, although the filter diameter may be smaller than the outside diameter of the lens barrel, there is no problem with vignetting, since the opening of the lens is so much smaller than the diameter of the barrel.
2. As above, but with a double filter ring (available only for nos. 2.0 to 8.0). This gives you female threads in front of the filter, so you can mount a shade in front, for $150.
3. Four inch square filters with a working area of about 3.5 inches for large diameter and wide angle lenses, designed for Lee and other drop in filter-holder systems. Available in 2.0 (working size 3 x 3 inches), 2.8 (working size 3.5 x 4 inches) and for 4.0 to 8.0 (working size 4 x 4 inch), for $180.
Call (800)-222-0325 to order or for more details. Commercially available step-up or step-down rings allow the filters to be used with any lens on any camera. An adjustable adapter is available for $98 that allows the filters to be mounted on all lens barrels up to 4.5 inches in diameter.
Here are a few tips to help you fight moiré:
1. Make sure you evaluate a printed image, not the preview on the monitor. Since the resolution on paper is much higher, the print will look better!
2. Adjusting the unsharp masking will help increase image sharpness.
3. Distance from the lens and camera angle can have dramatic effects on moiré, so experiment, if needed.
4. Longer exposure times may result in less moiré.
5. Apertures smaller than f:16 often result in less moiré
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