Abstract

The first step in selecting a starting configuration is a careful study of requirements. Vignetting, mechanical limits, unusual pupil requirements, unusual distortion specification or allowance, resolution, and method of evaluation are basic requirements. Question the client: Some specifications may be rigid, and others may be target values. The client may know a configuration you have missed. Usually one starts with a known model and plans to make modifications; otherwise, one has no reason to expect success. Useful configurations to consider as added components are field flatteners, aplanatic surfaces, surfaces with the A-stop imaged near the center of curvature, and the separated doublet for correcting high-order spherical aberration. The plan should be based on full consideration of all limiting aberrations of the model. A well-reasoned conjecture about the cause of limiting aberrations and a plan for their alleviation is always worth a hard try. Sometimes thin-lens algebraic solutions of firstorder requirements, or even third-order aberrations, can be useful—especially for relay systems. A simple interactive program, or even a programmable calculator, can be invaluable in converting to a thick-lens starting model. Finally, a starting model can be based on the conjecture "What would happen if...?"

© 1990 Optical Society of America