Achromatic Systems
Control of chromatic aberration, or control of focus shift as a function of color, is an important aspect in imaging system design. Normally, a variety of carefully chosen optical materials (glasses) are selected for the lens system to control chromatic aberration. While hundreds of different glasses are available, only a handful of plastic lens materials are readily available. This shortage of different materials makes the traditional control of chromatic aberration with plastic lenses, or with inexpensive imaging systems, difficult.
By modifying the optical system with a special-purpose wavefront mask the imaging system can be completely corrected for chromatic-aberration. The actual amount of chromatic aberration need not be known or measured and can even be changing with time, as a function of temperature for instance.
Figure 1a. Standard, chromatic aberrated system.
Figure 1b. Cubic Phase Mask system.
The above images were produced from a severly chromatically aberrated two-lens singlet-based imaging system. For technical information on the system, see the ray-intercept plots. The left image is a composition of three greyscale images of a chrome-on-glass Air Force resolution target each containing different red, green, or blue color information. The right image was formed from the same system with the addition of a cubic-phase wavefront mask placed at the aperture stop and image-independent digital filtering of the resulting images. The modified optical/digital imaging system shows no effects of the chromatic aberration that severly affects the traditional imaging system. The optical/digital system is then achromatic!
Ray Intercept Plots
