Apochromatic vs achromatic

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What isan achromatic lens used for

This month's fantastic issue showcases documentary storytellers-photographers worldwide. We are pleased to feature an exclusive interview with internationally acclaimed photographer Alain Schroeder, highlighting three of his unique projects: 'Muay Thai Kids,' 'Coal Survivors,' and 'Kid Jockeys.' With over forty years in the industry, Belgian photographer Alain Schroeder travels the globe to capture compelling stories that spotlight social issues, people, and their environments.Zoe Larson presents her latest project, which documents Henry the Asaro Mudman and explores hidden tribes in Papua New Guinea. Outstanding photographer Nicola Ducati features two intriguing projects: 'Sikerei: We Are Lost Together' and 'Steel Life.' Christian Kieffer shares a documentary project dedicated to Colombia's Kogi people and the Tunkeka community. Hadi Dehghanpour provides insight into workers' lives in the saffron fields known as 'The Red Gold' in the Khorasan Razavi province of Iran. Jerzy Wierzbicki exhibits his captivating artistic project, 'The Empty Quarter,' set in the magical deserts of Oman. Pygmalion Karatzas continues to fuse the boundaries between topographic/representational and expressionistic/pictorial iconography through his two projects, which focus on Salt Pans and Mount Athos in Greece. Omair Farooq showcases a compelling project dedicated to the resilient villagers who are deeply connected to the landscape in the suburbs of Aligarh—a city renowned for its prestigious university and vibrant lock-making industry. Enjoy!On the Front Cover: Project: Muay Thai KidsAlain Schroeder © All rights reserved. See the exclusive interview on page 12On the Back Cover: Gimisave WomanZoe Larson © All rights reserved.See the article on page 70

Describing a lens consisting of two or more optical components (elements), intended to correct for chromatic aberration. Commonly used as the objective of small refractors, the achromatic lens (or achromat) was invented in 1729 by the English optician Chester Moor Hall (1703–71) and first manufactured commercially by J. Dollond in 1758. It has one element of crown glass and another of flint glass. The dispersion (1) of the crown glass compensates for the chromatic error of the flint glass, while still leaving some refractive power. The two-element design is termed an achromatic doublet. It is practically impossible to correct all wavelengths of light, however, and most lenses adopt a compromise, bringing two particular wavelengths to a common focus, thus reducing the false colour. A lens that corrects for more than two wavelengths is termed an apochromatic lens.