 Cristina |
UV filter? Here's an example:
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William Schuette |
Hi Cristina, although your examples did not post, it sounds like you are talking about Chromatic Abberation, which generally appears as a blue/purple aura. This is not caused by UV light and would not be resolved by a UV filter. CA typically occurs in high contrast situations such as something that is strongly backlit. It is a product of both your lens and sensor. Try to avoid high contrast situations with the particular lens/camera combination. Using a circular polarizer might help reduce contrast and therefore reduce potential CA. Lastly, many of the raw converters such as Capture NX and DXO Optics Pro can reduce or eliminate CA. Bill
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Alan N. Marcus |
Hi Cristina, The camera lens bends (refracts) light rays causing light rays to bend inward (converge). This action forms an image of the outside world on the surface of the digital chip inside, at the back of the camera. Images that form close to the lens are small whereas images that form further away from the lens, are larger (magnification). We measure the distance, lens-to-chip to derive what focal length the lens is operating at (when the camera is focused on a distant object). The amount of convergence fashioned by the lens is different for each color. The blue image forms first thus it is closes to the lens, next comes the green followed by yellow then orange then red. The difference in distance between the various colors is minuscule, nevertheless, the red image, being further away from the lens is slightly bigger than all the others. The blue image, being closes to the lens is the tiniest. These variations in focal length induced by color, we call chromatic aberration. The result is a purple fringe around images of objects. Chromatic aberration will be most obvious when you are zoomed out to near maxim magnification. Most all good digital editing software feature routines that nullify purple fringing. Opticians learned years ago, how to minimize this aberration. The bad news is, they have never figured out how to completely eliminate it. Your camera lens is constructed of multiple lens elements. Some are converging, shaped with a bulge in the center like a lintel seed. Others are concave (thinner in the center like the inner surface of a sphere). Some are made of heavy dense glass, others are made using a lightweight glass. These measures produce a lens called an “achromatic” that minimizes aberrations. Perhaps, if you study optics, you might be the one to triumph over this and other lens defects. Alan Marcus (marginal technical gobbledygook)
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