BetterPhoto Member |
What's wrong with this camera (or my shooting)?
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Jon Close |
The green spots are mirror reflections of the bright light points in the photos. Typical causes are from using a filter (especially inexpensive non-coated or single coated), or possibly reflections onto an uncoated rear lens element off the glass covering the digital sensor. In each case the effect is exacerbated by overexposure. The first picture of the moon is at ISO 200, f/5.6 and 1.3 seconds. Proper exposure of the moon - which is very brightly lit by sunlight - at ISO 200 would be something like f/8 and 1/400 sec.
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Alan N. Marcus |
Hi Jeffrey, Sorry you had this experence. What you have is ghost flare, an internal reflection that made it way to the image plane. Over exposure give emphasis. A helpful countermeasure is a lens hood. Bright object just out of the field of view are sometimes responsible. The color you see is reflected light from a coated optical surface. The coating was specialized to control the transmission of red and blue light (magenta). Green was reflected as this the color that is opposite green (its complement). You are finding out that flare is devastating! We wish the camera lens could be constructed with just one glass element. Such as design has minimal flare. Sorry to report, a simple lens has so many aberrations for our needs. When we ask for a camera with expanded picture taking capabilities, we are forced to make the lens complex. Complex means many glass lens elements, each with a polished glass surface. Some elements cemented together using transparent glue, others set close with an air space in-between. When light strikes a lens surface three things happen. About 4 – 6% of the light is lost due to refection at each interface. Most often it is reflected backwards and hits the next forward element and is thus re-reflected. The bottom line is; all these reflections become stray light and we call it flare light. Most finds its way to the film/chip and intermingles with the image forming rays. Flare is devastating; it takes a terrible toll causing a loss of image contrast. Lens coating to the rescue: The coating thickness is the key: Alan Marcus
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