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Photography Q&A
Autofocus mechanism
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<blockquote data-quote="Stoshowicz" data-source="post: 370167" data-attributes="member: 31397"><p>I spent a couple hours researching this last night. there are different kinds and causes all due to the lens handling of various wavelength light.</p><p> You and I are getting a lateral (radial) misalignment of the warm and cool tones.. which gets worse as one looks closer to the periphery moving out from the center. It has the effect of offsetting the colors which is why you see two colors- one on each side . The camera raw lens correction should work pretty good at realignment since the ' individual ' colors arent really out of focus. There are also two possible axial forms of CA, which arent what we have. With purple fringe blue is focused behind the sensor , the greens are smack on the sensor , and the reds are focused in front of the sensor. since the reds and blues are out of focus, they are both spread out as larger images than they should and since they overlap without the greens -what you see is a single color purple halo. This isnt as easily correctable since even if you blurred the green channel to the same extent ( so as to line up with the other two) your image would be softened to the same extent. </p><p></p><p>( the other axial CA shows as soft radial color bands at distance from the center of the lens like a green magenta rainbow. </p><p></p><p>I'd suspect that the UV filter could be misaligned -tilted cross-threaded or just faulty - causing the increase in lateral CA, because knocking out the UV should actually be eliminating a wavelength of light which isnt usually well handled for CA , by lenses, but may affect sensors.</p></blockquote><p></p>
[QUOTE="Stoshowicz, post: 370167, member: 31397"] I spent a couple hours researching this last night. there are different kinds and causes all due to the lens handling of various wavelength light. You and I are getting a lateral (radial) misalignment of the warm and cool tones.. which gets worse as one looks closer to the periphery moving out from the center. It has the effect of offsetting the colors which is why you see two colors- one on each side . The camera raw lens correction should work pretty good at realignment since the ' individual ' colors arent really out of focus. There are also two possible axial forms of CA, which arent what we have. With purple fringe blue is focused behind the sensor , the greens are smack on the sensor , and the reds are focused in front of the sensor. since the reds and blues are out of focus, they are both spread out as larger images than they should and since they overlap without the greens -what you see is a single color purple halo. This isnt as easily correctable since even if you blurred the green channel to the same extent ( so as to line up with the other two) your image would be softened to the same extent. ( the other axial CA shows as soft radial color bands at distance from the center of the lens like a green magenta rainbow. I'd suspect that the UV filter could be misaligned -tilted cross-threaded or just faulty - causing the increase in lateral CA, because knocking out the UV should actually be eliminating a wavelength of light which isnt usually well handled for CA , by lenses, but may affect sensors. [/QUOTE]
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