1. In 1765, he introduced an astronomical instrument fitted with two achromatic lenses . 2. This lens had the largest aperture of its day for an achromatic lens . 3. Had he done so, he would almost certainly have invented the achromatic lens . 4. He suggested using two achromatic lenses of " six inches focus " placed apart. 5. The 1955 model came with a meniscus lens, later replaced with an achromatic lens . 6. It is a refractor with double achromatic lenses of 40 cm diameter and has 5m focal length. 7. The difficulties of fabricating two disks of optical glass required to make a large achromatic lens were formidable. 8. Achromatic lenses are corrected to bring two wavelengths ( typically red and blue ) into focus in the same plane.9. The glass blanks were ground and polished into a 12-inch achromatic lens by Brashear & Co in 1920. 10. Malcolm used an original design incorporating achromatic lenses like those used in telescopes, and improved the windage and elevation adjustments.
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