(Purple Fringing Lesson)
Tech note: My oh my! Don't look at the full-sized image! The purple fringing and/or Chromatic Aberration here is terrible!! Is this the result of shooting wide-open at f/1.4? Yes! (in part) Lesson: (1) Avoid shooting with a wide-open lens in high contrast scenes. (2) Avoid overexposing highlights (e.g. specular reflections and bright sky behind dark objects).
References: en.wikipedia.org/wiki/Purple_fringing says "Axial chromatic aberration is more subject to reduction by
stopping down the lens than lateral chromatic aberration is, so the
purple fringing can be very dependent on f-number.
Purple fringing is usually attributed to chromatic aberration, although it is not clear that all purple fringing can be explained this way. Other attributed causes of purple fringing in digital photography include many hypothesised sensor effects:
•Chromatic aberration in each CCD cell (microlenses)
•Digital noise in dark areas
•Image processing and interpolation artifacts (almost all CCDs require considerable processing)
•Stray ultraviolet light
•Stray infrared light
•Image bloom from overexposure
•Leaks between cells of the CCD
Commonly advocated methods of avoiding purple fringing include:
•Avoid shooting with a wide-open lens in high contrast scenes.
•Avoid overexposing highlights (e.g. specular reflections and bright sky behind dark objects).
•Shoot with a Haze-2A or other strong UV-cut filter.
Post-processing to remove purple fringing (or chromatic aberration in general) usually involves scaling the fringed colour channel, or subtracting some of a scaled version of the blue channel."
"Photography - The term "purple fringing" is commonly used in photography, although not all purple fringing can be attributed to chromatic aberration. Similar colored fringing around highlights may also be caused by lens flare. Colored fringing around highlights or dark regions may be due to the receptors[clarification needed] for different colors having differing dynamic range or sensitivity -- therefore preserving detail in one or two color channels, while "blowing out" or failing to register, in the other channel or channels. On digital cameras, the particular demosaicing algorithm is likely to affect the apparent degree of this problem. Another cause of this fringing is chromatic aberration in the very small microlenses used to collect more light for each CCD pixel; since these lenses are tuned to correctly focus green light, the incorrect focusing of red and blue results in purple fringing around highlights. This is a uniform problem across the frame, and is more of a problem in CCD's with a very small pixel pitch such as those used in compact cameras. Some cameras, such as the Panasonic Lumix series and newer Nikon DSLRs, feature a processing step specifically designed to remove it. On photographs taken using a digital camera, very small highlights may frequently appear to have chromatic aberration where in fact the effect is because the highlight image is too small to stimulate all three color pixels, and so is recorded with an incorrect color. This may not occur with all types of digital camera sensor. Again, the demosaicing algorithm may affect the apparent degree of the problem."
Vandalized statue shown here 24 Sept. 2009, without the Peregrine Falcon which was stolen. "Seasons come and seasons go" - A bronze sculpture of a Native American with Peregrine Falcon, Bear, Heron, etc., reflecting life in the Morro Bay estuary, Aug. 2, 2002, Sculptor Mark Greenway. This sculptural tribute to life in the estuary was commissioned by Diane Blakeslee. 08 Sept. 2009. Mary Golden, Executive Director CCNHA reports that the Peregrine Falcon shown here was stolen and the statue vandalized. "Dan Falat informed me today that someone stole the Peregrine Falcon portion of "Seasons Come [and] Seasons Go" sculpture outside of the museum. It was mounted on 8/2/02. Diane Blakeslee donated the piece which was $25,000. I just spoke with the artist, Mark Greenaway. He said it had to have been someone using considerable force since it was welded on securely. he is guessing someone tied it to a car and it snapped off. The sculpture itself has 30 inch bolts into concrete and then in to rock, so the sculpture itself shouldn't go anywhere. He said it was a one of a kind, and that the mold was destroyed. He said to replace it would cost $7,000, and that does not cover his time, just the materials, mold and foundry. He also said he studied Peregrine Falcons, watched videos of them flying and called in a professional birder to get the aspects of flight done correctly. He said it was a labor of love. I'm thinking about writing a press release about this, and Mark is sending me some enlarged photos of the Falcon." See more photos of this statue in the set www.flickr.com/photos/mikebaird/sets/72157613035145450/ . Photo by Michael "Mike" L. Baird, mike [at} mikebaird d o t com, flickr.bairdphotos.com; Canon 5D, Canon 50mm f/1.4 handheld