There is an opportunity for extra credit listed below. You may complete 2 (TWO) . Each one should be a double spaced, one page entry with one inch margins, 12pt font and name on the top . Each topic paper is worth 5 points. *****To open the link, click on the assignment “Extra credit Opportunity” above – this is where you can submit your papers! References (with whatever format you are comfortable using)should be included at the end of your paper. Please attach using one of the following formats (.doc .pdf or .txt). Please include both (if you do both)papers in one file. Include your last name and topic(s) in the name of your filename: mayereyesandsky.doc Yes I know that this impacts the grade total – the Grading Scale in the syllabus is correct -please refer to that! Topic is: Chromatic aberration in a lens

Essay

Chromatic Aberration

Chromatic Aberration or  color fringing is an optical problem which occurs when a lens is not able to bring all wavelengths of color to a common focal plane or when the wavelengths are focused at different positions in the focal plane. In uncorrected lenses, the result is colored fringes in the images produced.

This phenomenon is caused by lens dispersion in which different colors of light travel at different speeds while passing through a lens, causing a blurred image. Noticeable colored edges may also appear around objects, mainly in high-contrast situations.

Since the refractive index for each wavelength is different in lenses, two types of Chromatic Aberration result: Lateral Chromatic Aberration and Longitudinal Chromatic Aberration

Longitudinal Chromatic Aberration (LoCA) occurs when different wavelengths of color fail to converge at a common  point after passing through a lens. A lens with this problems may show fringing around objects throughout the image including center. It  can be reduced by stopping down the lens.

Lateral Chromatic Aberration results when different wavelengths of the color incident at an angle focus at different positions along the same focal plane. This type does not show up in the center. It is only visible towards the corners of the image in high-contrast areas. It can be eliminated or reduced in post-processing software.

In many lenses, both longitudinal and lateral chromatic aberrations are present at the same time and can only be removed by the above techniques. Chromatic aberration, however, remains problematic in most prime and zoom lenses.  Many modern DSLRs incorporate special in-camera post-processing techniques to reduce chromatic aberrations.

References

Johnson, Micah K., and Hany Farid. “Exposing digital forgeries through chromatic aberration.” Proceedings of the 8th workshop on Multimedia and security. ACM, 2006.

Kidger, Michael J. “Fundamental optical design.” SPIE, 2001.

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