UniServe€Science News: Newsletter of the Science Software Clearinghouse Vol. 3, March 1996


An interactive tool for teaching geometrical optics

John O'Byrne

Raytrace is clearly targeted as an educational tool. It is not a general purpose ray tracing program and does not provide some of the capabilities of such programs. Nevertheless, the facilities it provides are quite impressive and it could be a very useful teaching tool if used intelligently.

The program can be mastered by a course instructor with a day or two of practice (familiarity with CAD software may help). However, in my opinion it is too complex to present to an average first or second year university student for a brief laboratory or tutorial session. It would be suitable if the student has enough time to master the basic operation of the program, as in some form of project work. However the scripting capabilities illustrated in the demonstration provided with the program provide a means of tailoring the extensive program capabilities to the student capabilities. The students could do most of the work by following the directions provided by the script. The script would also allow some of the most time consuming details to be simply provided. The scripting is a new feature documented in the on-line help, but not yet in the manual. It is essential that it be comprehensively documented to allow instructors to use it.

Generating shapes such as lenses is a little tricky. Drawing the curves is somewhat non-intuitive and there is plenty of room for students to make a mistake and waste considerable time overcoming it. These more complex figures could be better drawn by a script or simply provided in a new library generated by the instructor. The other obvious way to overcome these drawing difficulties is to specify a figure using numbers (e.g., surface radii, spacings) provided in an input file. This capability is common in general ray tracing programs, but would still be a valuable addition to Raytrace for those circumstances where it is actually easier than drawing the figures.

One other small addition would be an explicit menu item to cancel any current operation. Although ESC will do this, you need to know this and there is no menu item the user can find corresponding to it.

Having mentioned some reservations, it would be wrong to leave the impression that Raytrace is not an excellent program. Among its most attractive features is the ability to move rays or sources or change refractive indices and immediately see the effect, including changes in distances and angles. Another is the ability to trace around an object and see the corresponding aberrated image traced out.

In summary, Raytrace can be a valuable teaching tool if implemented with appropriate assistance for the inexperienced student. It provides many more features than the limited programs which we currently use in our first year laboratory (based on the CT programming language). It is also better suited to demonstrations in lectures than the general ray tracing program we have used to date.

John O'Byrne

John O'Byrne is a lecturer in the School of Physics at the University of Sydney

Requirements: PC running Windows 3+
Author: Dr Ian Moore, Queensland University of Technology
Cost: $95
Supplier: IME Software, PO Box 1133 Toowong QLD 4066