Designing a telescope to look closely at stars and planets, even though you are nearsighted and don’t have glasses. There is a good chance that this was the case with the 17th-century natural scientist Christiaan Huygens, without his knowing it. This is the conclusion of astrophysicist Alex Pietrow in a study of the telescopes of the well-known Dutch physicist and astronomer.
There was probably nothing wrong with Huygens’ telescope lenses, says Pietrow in the journal The Royal Society. But nevertheless his stargazers were a lot less sharp than was possible at the time. According to Pietrow, this is probably because Huygens had a slight eye defect, which prevented him from optimally adjusting the ratio between the two lenses of his telescope, among other things.
Posthumous glasses advice
Today’s telescopes can be rotated to focus, the researcher explains when asked. “But that was not possible then: telescopes were fixed in a certain focus.” Huygens had to try out different lenses and ratios to build the perfectly working telescope. “He played with the lenses and pulled them apart with his hands until the image was sharp enough for him.”
Based on his findings, Huygens formulated formulas that allowed him to build telescopes in different magnifications. “But if you now simulate them according to those formulas, you end up with a telescope that is out of focus,” says Pietrow. He attributes this to myopia, which also affected Huygens’ father – the famous poet Constantijn – and his brother. In other words: Huygens may have seen clearly through his telescope, but others did not.
Pietrow calculated what that would mean now: that Huygens would have needed glasses with a strength of -1.5. Then his formulas would be correct. “This is probably the first ever posthumous glasses prescription,” he says.
Probably Huygens himself was not aware of his deviation, because it was too limited to cause problems in daily life. “So he probably unconsciously incorporated this eye defect into his designs,” Pietrow thinks.
A plausible conclusion, says Tiemen Cocquyt. The physicist is curator at the Rijksmuseum Boerhaave in Leiden, where dozens of Huygens’ homemade lenses are on display. “If you calculate all the formulas, you come to the conclusion that Huygens could have made better telescopes. And that is surprising, when you see how far his theory reached. So there must have been a limitation.”
But, says Cocquyt, who has done research on 17th-century telescope lenses in the past: “It’s not so much about whether Huygens wore glasses or not. For me, this research mainly shows that the interaction between theory and practice has a played a major role in Huygens.” Through trial and error, Huygens was able to link his ‘lens theory’ and ‘telescope practice’ like no other, he says.
And then, according to Cocquyt, there is the social component. The curator and his colleagues have always wondered why Huygens made so many telescope lenses and why they were not actually distributed outside the family. “It was kind of a family business. This research shows that there might have been a charming explanation for that: myopia ran in the family. So maybe the telescopes were completely tailored for father and sons.”