The designers of digital cameras (cameras with CCD detectors) have a significant advantage over the designers of film-based cameras. Lenses for film-based cameras must produce a high-quality image directly on the film plane, and there is no possibility for post-processing. When the detector is a CCD chip, and the camera has an on-board computer, there is significant scope for electronic post-processing of the image to remove aberrations.

The simplest example is distortion correction. Because distortion only affects the location of the image, and does not affect the quality, it is possible to un-distort the image electronically. This relieves the lens designer of the need to minimize a significant aberration. Much work is also being done on compensating other aberrations, given a knowledge of the OTF of the lens. Using the GBIA feature allows such image correction algorithms to be tested prior to building expensive prototype optics, and the work we have done recently on improving the speed of this feature means that this work can be done in almost real time.

Note that diffraction is not considered by the GBIA: if diffraction effects are important, look at the Diffraction Image Analysis and Extended Diffraction Image Analysis features instead.

Finally, the same calculation can be performed non-sequentially if desired, especially if monochromatic images are required. The non-sequential SLIDE object can be used to place a .bmp or .jpg graphic in an optical system. It can also be used in hybrid-mode, so that you can place a slide object at any location in a sequential optical system too.

The advantages of performing these calculations in non-sequential mode include:

• More realistic modeling of sources is possible in non-sequential mode, including the use of measured source data like Radiant Sources. See this article for more information on source modelling.
• The effects of ghost pupils and images on the final image can be seen
• The effects of opto-mechanical stray light, in which light reflects from the mechanical components of the system can be included

This disadvantage is mainly speed: non-sequential ray-tracing is inherently slower than sequential, and ray-tracing CAD objects is slower than tracing parametric optical objects. The other disadvantage is that the NSC detector must be traced one wavelength at a time, the data exported, and the recombined to produce the full color image (this is not necessary if the image is monochromatic). Therefore the sequential analysis should be performed first. If the sequential system gives inadequate performance, then nothing that is considered by the non-sequential ray-trace will improve things: the effects considered by the non-sequential trace generally only degrade performance.