In deflectometry, a camera images fringe patterns that have reflected off a surface under test, so that a system can deduce a map of the surface slopes from the deviation of the projected fringes, and from that determine the surface shape. Credit: Mahr

Getting the measure of aspheric and freeform lenses

Lens features have been getting too small to properly characterise – but metrology providers are catching up, finds Andy Extance

Measure for measure

Keely Portway looks at some of the latest advances in light-based test and measurement techniques

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