Chromatic aberration could only be corrected for all wavelengths if the index variation was linear with wavelength but, as shown in figure 1, this relationship is distinctly non-linear. Secondly, these equations only ensure that the focal lengths are equal at the C and F wavelengths. Firstly, the assortment of glasses with different indices and V-values is limited, so an exact match may not be found for any combination. However, when correcting chromatic aberration, two further problems have to be addressed. The exact combination of lens powers and V-values can be derived using simple simultaneous equations. By combining lenses of two different materials, chromatic aberration can be reduced significantly. ![]() ![]() Here, n represents the index of refraction. The material-dependant dispersion can be described by the V-value, where When designing visible systems such as microscope objectives, optical designers start by assessing the performance at three suitably spaced wavelengths, conventionally 656 nm (red), 588 nm (yellow) and 486 nm (blue) - known as the Fraunhofer C, d and F lines. Achromatic and apochromatic systems offer suitable solutions. This defect must be controlled, particularly in demanding fields such as microscopy. As a result, a simple lens can be perfectly focused for one wavelength, but badly out of focus for other wavelengths. the change in refractive index with wavelength) of any optical media. Chromatic aberration is one of the main image defects in optical systems.
0 Comments
Leave a Reply. |