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Tutorial 11 - Secondary color

This video shows how to calculate the secondary color in an achromatic lens. Secondary color is defined as the defocus from the central wavelength to the wavelength extremes. Recall that in an achromat the wavelength extremes focus at the same location. 

No History lessons:)


1.Calculate the secondary color for a 78 mm achromatic lens made of N-BK7, N-SF6.
2.Calculate the secondary color in a 50 mm achromatic lens made of S-FPL53 and S-BSM81.
3.Standing around the water cooler, another engineer says he bought a 100 mm focal length achromat. Assuming the crown and flint fall exactly on the glass line what is the secondary color (distance in mm or µm)?
4.A doublet will have low secondary color if:
A.The crown and flint have similar partial dispersion
B.The crown and flint have very different dispersion
C.Has one glass off the normal line
D.All of the above
5.Lateral color (magnification change with wavelength) can be considered a function of axial color (true or false?)
An optical material has an index of 1.92245 at D light, 1.90916 at C light and 1.95800 at F light.
6.What is the partial dispersion?
7.What is the dispersion?

Solutions can be found here.