Longitudinal Chromatic Aberration Effect On Color

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Author	Replies: 3 / Views: 1,715
rmpsrpms Pillar of the Community United States 4038 Posts	Posted 10/05/2011 01:22 am I took some pics of my reference 1921 Morgan dollar with a (name/model withheld) lens to show what Longitudinal Chromatic Aberration (Long CA) looks like and how it can affect the apparent color of a coin. The phenomenon is most visible at 100% magnification so I cropped the cornflowers out of 3 images: Focused Just Right; Focused High; and Focused Low. Have you seen this when taking pics of your coins? This is a big problem because it is not correctable in post-processing, unlike Lateral Chromatic Aberration, which can be corrected. What happens with Long CA is the parts of the coin that are in optimal focus are close to the correct color, but the high and low areas shift color one way or the other! Take a look at these images to see what I mean. Note there is VERY little difference in focus between these, basically just a nudge high and low from the critical focus point: Focused Just Right Focused High Focused Low Contact me for photographic equipment or visit my home page at: http://macrocoins.com Report this Post to the Staff

aladinslamp Pillar of the Community United States 3076 Posts	Posted 10/05/2011 03:05 am Hi Ray, I do see the difference between the just right and the high,,which is slightly our of focus, I need to look more closely at the low side to find the differences...I do appreciate your ever non ending points of view and studies,,, HIGH END points of view yet, down to earth explanations which one can grasp as we study...Thanks Gene Report this Post to the Staff
rmpsrpms Pillar of the Community United States 4038 Posts	Posted 10/05/2011 10:07 am Thanks Gene! I see the biggest difference between the "High" and "Low", with "Just Right" between the two. By the way, when I say "Low" it means the camera was closer to the coin than critical focus. With this lens, it also took moving the camera farther from critical focus on the high side to have the color change than it did on the low side. Just a slight move to the low side shifted the color quite a bit. I think this is why the "Just Right" image and the "Low" image look more similar. On my monitor, the difference significantly shifts the effective white balance, with "High" being very blue, and "Low" being very red, mostly showing up in the highlights. ...Ray Contact me for photographic equipment or visit my home page at: http://macrocoins.com Report this Post to the Staff
rmpsrpms Pillar of the Community United States 4038 Posts	Posted 10/05/2011 12:39 pm Here are overall pics of the coin. I won't say which is which, I'm hoping the color difference is obvious. Lighting is different from previous pics. Single light before, two lights on these. I don't see a lot of difference in the background color. I think this is because it's already out of focus and small differences in focal plane adjustment don't do much to the color mix. You can fairly easily see the difference between these in their histograms... Contact me for photographic equipment or visit my home page at: http://macrocoins.com Edited by rmpsrpms 10/05/2011 12:42 pm Report this Post to the Staff
	Replies: 3 / Views: 1,715

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