from Astro 2011. 7. 4. 16:37
Both the Deltrintem and the Jenoptem are classic devices with achromatic objectives and Porro prisms. At first those binoculars were equipped with a 4-element eyepiece without any anti-reflection coatings. During the WWII the producers started to cover their air-to-glass surfaces with a single anti-reflection layer of magnesium fluoride. In 1947 the binoculars got a new Erfle 5-lens eyepiece which was supposed to give a wide field of view with a minimum distortion level. In 1978 they started to use new multilayer coatings with a characteristic orange-purple hue.

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