
Using the ray fan
The ray fan is a plot of ray intercept (where the ray hits the image surface) versus pupil coordinate.
To create a ray fan window:
- Select from the menu Analysis > Fans > Ray

The ray is displayed as a function of the normalized pupil coordinate. Both a tangential and a sagittal scan is made, with the sagittal scan plotted as a dashed curve. For the tangential scan the y intercept of the ray is plotted. For the sagittal scan the x intercept of the ray is plotted. The curves can correspond to different field points at a constant wavelength, or to a particular field point with different wavelengths. The options button will summon a utility window that will let you change the number of points at which the ray intercept is calculated, the field(s) of interest, and the wave(s) of interest.
Options
Fan options
- Field
- Using the Field popup menu, select the field for which you wish to calculate. Select All to calculate for all fields.
- Wave
- Using the Wave popup menu, select the wave for which you wish to calculate. Select All to calculate for all waves.
- Number of rays
- The ray fan curves are generated by tracing rays in each of the sagittal and tangential planes, forming crossed lines across the pupil. Each line is sampled using the specified number of rays, for each field and for each wave.
- Color by
- Specify how the curves are to be colored. Options are to use the color of the corresponding field or wave, or to use the same color for all curves.
- Paraxial trace all rays
- Use paraxial propagation instead of full geometric optics propagation.
- Afocal analysis
- Plots the direction tangents ux and uy instead of ray coordinates x and y.
- Divide by focal length
- Plots the ray coordinates x and y divided by the focal length of the lens. This expresses the ray fan of a telescope in terms of angles in the object space.
- Plot sagittal curve
- If checked, the sagittal curve is plotted.
- Plot tangential curve
- If checked, the tangential curve is plotted.
- Subtract centroid
- Uses the centroid of the rays (on a per field and per wave basis) instead of the chief ray.
Plot options
- Scale only expands
- If checked, the scale of the axes only expands due to the action of sliders, etc. Useful when scanning through focus using the sliders tool.
- Axis tight on data
- If checked, the limits of the axes are chosen so that the data exactly fills the graph. If not checked the limits of the axes are chosen to give "nice" values at the extremes of the axes.
- Show legend
- If checked, the names of the curves are presented in a list to the right of the plot.
- Multiplot
- If checked, each field point gets its own graph.
- Transpose axes
- If checked, abscissa and ordinate are interchanged on the graph.