Point sources are very useful in the design of imaging systems, because the detected image properties of a point source can be used to accurately describe many aspects of image quality.

However, extended sources are very useful for visualizing distortion (especially non-radial distortion), checking image orientation or polarity, color separation, and for qualitatively illustrating overall system performance.

ZEMAX supports two types of extended sources. A simple ASCII format that is useful for making bar targets, letters, squares, and other simple shapes is supported. For complex 24 bit color images ZEMAX supports the standard Windows BMP and .JPG formats. Images defined in either format may be used as sources, and the detected image may be viewed for any optical system using user defined detector properties.

Once an extended source file is created, it can be scaled, rotated, inverted, and placed at any position in the field.

The extended source imaging features in ZEMAX account for image distortion, aberrations, and transmission, which is generally field, pupil, and wavelength dependent.

The Relative Illumination (RI) feature computes the relative illumination of an optical system as a function of radial field coordinate. It is useful when you need to produce an image with defined illumination properties: usually (but not exclusively) a flat illumination surface is desired. The screenshot below shows the variation of illumination calculated at the film plane of a simple camera lens

The Illumination XY Scan computes relative illumination for an extended source along a line across the image surface.  This is similar to the relative illumination feaure, with the added capability to estimate the relative illumination for non-uniform extended sources. For systems with complex source properties, the illumination XY scan estimates illumination by Monte Carlo ray-tracing combined with conventional Relative Illumination computations.

The above plot shows the illumination scan of a complex source being imaged through a conventional imaging system.

The Illumination 2D surface is similar to the XY scan, except the whole illumination surface is shown, and can be drawn as a contour plot, isometric surface, grey scale or false colour map. Here is a decentred and rotated image (the Focus Software logo) imaged off-axis through a conventional imaging system. Over 1 million rays were traced for this example, and you can use up to 5 billion!

The resolution of the screenshot has been reduced by the web graphic file format: much higher resolution is possible. The effects of aberrations in the image can be clearly seen. The optical system has single-layer Magnesium Fluoride coatings on all surfaces: the efficiency of 93.8% shown on the graphic is due mainly to residual reflections. All illumination calculations can be made polarisation-sensitive, so that system transmission (anti-reflection coatings, filters coatings, glass absorption etc) can be taken into account. This gives ZEMAX the most complete illumination analysis of any lens design code!