Hybrid refractive–diffractive elements offer a similar level of aberration control to the conventional doublet with approximately half the volume of material. The design principles of infrared elements are discussed. It is shown that, in order to match the performance of the conventional doublet, a general meniscus hybrid with an aspheric surface is required. The potential advantages are illustrated to good effect by a series of design examples, including a Petzval objective for the 3–5-μm band.
© 1992 Optical Society of America
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