The era of 1750s was an exciting time in the technology scene of England. Marine navigation of the empire demanded better time keeping and ever more precise celestial observation. Educated public was keenly interested in astronomy, partly from beliefs (still strong in our time) that celestial bodies determine our fate, partly from genuine desire to understand the Universe. Fortunes were made in manufacturing watches, navigation instruments, and telescopes.
Although refractive (lens-based) telescopes were already well known at that time, they suffered from chromatic aberrations, because of light dispersion in glass: light with different wavelength (color) propagates with different speed and thus gets focused at different distances from the lens, which creates colored fringes in the image. It was widely believed, due to Sir Isaac Newton's works, that chromatic aberration cannot be corrected with lenses. However, some scientists kept pursuing this lead, including Leonhard Euler, who proved theoretically that such lenses can exist.
An unlikely hero in this story, Chester Moore Hall was a barrister (a lawyer, don't confuse with barista), an educated men of independent means, and amateur optician. He surmised that since we don't see color fringes when using our bare eye, it must correct chromatic aberrations by some unknown mechanism. Since eye consists of refractive humours of different kinds, which are essentially lenses, a combination of glass lenses may also have the properties of color distortion correction. He succeeded in finding a lens pair which would do this job, by combining a positive and a negative lens of two dispersion types (crown, low dispersion, and flint, high dispersion). He wanted to keep his invention secret and ordered the two lenses from two different opticians, so each of them couldn't reverse-engineer his design. He didn't have time or desire to make a profit and fame of it, and it was designed solely for his own home-built telescope.
From there the story becomes a nerd blockbuster. The two opticians whom Hall ordered his lenses sub-contracted their orders to the same lens maker, George Bass. He realized that the two orders are from the same customer, so there must be some secret which the customer wanted to keep. Bass found the secret - the two lenses placed next to each other cancelled the chromatic aberration. Bass didn't keep the secret and started producing achromats and sharing the idea with others. The cat was out of the box.
In the 1750s Bass shared it with John Dollond, who recently started a business of making optical instruments with his son Peter. John Dollond immediately realized the importance of the idea, performed optical experiments to study the topic, and published a comprehensive paper in 1758 which made him famous and won him the Copley Medal of the Royal Society, the most prestigious scientific award in the United Kingdom, an honor that can be possibly compared to winning a Nobel in our time.
John Dollond also patented the achromat design, despite the fact it was already known and practiced by others, and him being not the original inventor. However, the Hall's original invention was never published, while Dollond took the idea, performed scientific experiments, re-designed the lens and published it in a way accessible to others. Unfortunately John Dollond suddenly died in 1761 at the age of 54, at the peak of his fame.
After John Dollond's death his son Peter launched commercial production of achromatic telescopes and also took action against several London opticians who "infringed" his father's patent. He soon was counter-sued by thirty-five opticians for exploiting the patent on invention which was known and practiced before. This led to a long and bitter court fight, which Peter Dollond eventually won. The court ruled that although Hall is the original inventor of achromat, it was Dollond who had the merit of bringing it before the public as a useful invention.
Peter Dollond later became famous for inventing apochromatic lens, which corrected 3 colors instead of two as the achromat. He continued the optical business he started with his father. Dollond telescopes for terrestrial use were amongst the most popular in Great Britain and abroad for over a century. Their company, Dollond and Aichison, existed for more than 250 years, famous for the quality of their instruments. During the recent market crisis of 2009 they merged with Boots Opticians due to financial difficulties.
References
Chester Moor Hall, Britannica.com.
John Dollond, Encyclopedia.com.
Peter Dollond, Wikipedia.
Peter Dollond answers Jesse Ramsden, archive of the Museum of Science.
Dollond and Aitchison, Wikipedia.
Although refractive (lens-based) telescopes were already well known at that time, they suffered from chromatic aberrations, because of light dispersion in glass: light with different wavelength (color) propagates with different speed and thus gets focused at different distances from the lens, which creates colored fringes in the image. It was widely believed, due to Sir Isaac Newton's works, that chromatic aberration cannot be corrected with lenses. However, some scientists kept pursuing this lead, including Leonhard Euler, who proved theoretically that such lenses can exist.
An unlikely hero in this story, Chester Moore Hall was a barrister (a lawyer, don't confuse with barista), an educated men of independent means, and amateur optician. He surmised that since we don't see color fringes when using our bare eye, it must correct chromatic aberrations by some unknown mechanism. Since eye consists of refractive humours of different kinds, which are essentially lenses, a combination of glass lenses may also have the properties of color distortion correction. He succeeded in finding a lens pair which would do this job, by combining a positive and a negative lens of two dispersion types (crown, low dispersion, and flint, high dispersion). He wanted to keep his invention secret and ordered the two lenses from two different opticians, so each of them couldn't reverse-engineer his design. He didn't have time or desire to make a profit and fame of it, and it was designed solely for his own home-built telescope.
From there the story becomes a nerd blockbuster. The two opticians whom Hall ordered his lenses sub-contracted their orders to the same lens maker, George Bass. He realized that the two orders are from the same customer, so there must be some secret which the customer wanted to keep. Bass found the secret - the two lenses placed next to each other cancelled the chromatic aberration. Bass didn't keep the secret and started producing achromats and sharing the idea with others. The cat was out of the box.
In the 1750s Bass shared it with John Dollond, who recently started a business of making optical instruments with his son Peter. John Dollond immediately realized the importance of the idea, performed optical experiments to study the topic, and published a comprehensive paper in 1758 which made him famous and won him the Copley Medal of the Royal Society, the most prestigious scientific award in the United Kingdom, an honor that can be possibly compared to winning a Nobel in our time.
John Dollond also patented the achromat design, despite the fact it was already known and practiced by others, and him being not the original inventor. However, the Hall's original invention was never published, while Dollond took the idea, performed scientific experiments, re-designed the lens and published it in a way accessible to others. Unfortunately John Dollond suddenly died in 1761 at the age of 54, at the peak of his fame.
After John Dollond's death his son Peter launched commercial production of achromatic telescopes and also took action against several London opticians who "infringed" his father's patent. He soon was counter-sued by thirty-five opticians for exploiting the patent on invention which was known and practiced before. This led to a long and bitter court fight, which Peter Dollond eventually won. The court ruled that although Hall is the original inventor of achromat, it was Dollond who had the merit of bringing it before the public as a useful invention.
Peter Dollond later became famous for inventing apochromatic lens, which corrected 3 colors instead of two as the achromat. He continued the optical business he started with his father. Dollond telescopes for terrestrial use were amongst the most popular in Great Britain and abroad for over a century. Their company, Dollond and Aichison, existed for more than 250 years, famous for the quality of their instruments. During the recent market crisis of 2009 they merged with Boots Opticians due to financial difficulties.
References
Chester Moor Hall, Britannica.com.
John Dollond, Encyclopedia.com.
Peter Dollond, Wikipedia.
Peter Dollond answers Jesse Ramsden, archive of the Museum of Science.
Dollond and Aitchison, Wikipedia.
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| The achromatic doublet. Image source. |
I Like to add one more important thing here, The Adaptive Optics Market is expected to be around US$ 4 Billion by 2025 at a CAGR of 40.5% in the given forecast period.
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