Thin-Lens Design Example
In thin-lens design, lenses are represented simply as lines located perpendicular to an optical axis. Rays are traced through a train of thin lenses in this example of a telescope and yield diagrams like the one shown below.
A “thin-lens” design is often useful before proceeding with a real thick-lens design.A thin-lens layout yields the approximate number of lens elements, lens diameters, focal lengths and spacings. It also provides the system overall length, back focal distance, and illustrates the space available for fold mirrors and prisms.
Thick lenses can be represented by two thin lenses with separation equal to the air equivalent thickness of a glass block of thickness equal to the lens thickness. A thin lens can be converted into a real achromat before proceeding to the detailed design by application of the formulas presented on the page “Thin-Lens Achromat”.
Thin-lens design can be performed with only a calculator, pad and pencil, but is best performed using a computer spreadsheet and/or computer optical design software due to the repetitive nature of the calculations. The equations employed are given in the sub-page, “Thin Lens Ray Trace”. It is a useful tool for system engineers as well as optical designers.
If available, a computer running software such as Zemax provides an enormously powerful thin-lens design tool. It allows the designer to find design solutions with many imposed constraints by using the same optimization algorithms used for real lens design