Thinking of Newton’s works, this question hit me: How great were optics back in Newton’s day? Was it easy for him to acquire quality optics with which to experiment in order to decipher the physics that governs the lenses and the images they create? true, he was nobility, but was it a painstaking process for him to weed out the unwanted effects esp present in poor optics (like distortion, etc.) from the true behavior of high-quality optics?
Most optics weren’t great – over a hundred years later a committee was set up to improve the quality of optical glass – but there were some very good examples. At the time Newton was working Anton van Leewenhoek was making his own superb single-lens microscopes, for instance.
That said, a lot of Newton’s work actually used some relatively simple optical shapes. He worked with prisms, and got reasonably good ones with flat sides. For his work on “Newton’s Rings” he needed a flat piece of glass (well-polished and reliably flat) and a good quality accurately spherical piece. Any deviation from a good flat surface and a good spherical one would have been immediately obvious, but Newton says nothing about any problems with the pieces he used.
Newton ground his own spherical mirror for his reflecting telescope, checking it against a glass spherical piece to check its figure, a procedure still used today in optics shops. Again, errors would show up easily with this technique.
The need for good refractive optics was already recognized by astronomers by Newton’s day, so there were places which had good quality optics. Errors would show up if you tried to get a good image of the moon or a planet. The achromat wasn’t invented until after Newton’s time, though. A big part of the reason for Newton’s inventing the reflecting telescope was to minimize the chromatic aberration by using a main element that didn’t introduce any. But an achromatic eyepiece had to wait until later.
Good lenses were available but not cheap in Newton’s day, and even when you paid handsomely you could not be sure of the quality. Galileo made his own lenses for his telescope, thus ensuring their quality, which had a lot to do with how he was actually able to make important discoveries with it, whereas other people of the time with telescopes could rarely see much of interest. However, Newton did not experiment very extensively with lenses. (Neither did he discover much of the physics that governs then and the images they create. The most important person of the era, in that regard, was probably Kepler, who worked out much of the geometrical optics of lenses, as well as discovering and explaining the retinal image of the eye. However, Snell, Descartes, Scheiner, and others also made important contributions.) The most important and critical element of Newron’s telescope was a mirror, and, as, CalMeacham notes, he made it himself. Very likely he made any lenses he needed too, from glass blanks.
The optical experiments that he is most famous for involved not lenses but glass prisms. He is said to have bought the prism with which he began these experiments from a country fair, where it was presumably sold as a novelty. Whether he later found it necessary to buy or make better quality prisms I do not know.
Newton was most decidedly not nobility. He was a farmer’s son, and an orphan to boot (his father died before he was born, and his mother abandoned him when he was three - he was raised by his grandparents). When he went to Cambridge, he had to pay his way through college as a sizar or subsizar (accounts vary), i.e., as a servant to the students who were actually noble and wealthy. He didn’t grow up in abject poverty, as his father had been quite a successful farmer (Isaac himself made a royal fuck-up of it when he briefly tried to run the farm), but he was certainly from a low social class, and not at all wealthy in comparison to actual nobility.
We read that Galileo started work on his own lense in the spring of 1609. He had found that three or so was the best magnification available with off the shelf lenses, and therefore learned to grind his own. By August, he had achieved about ninefold linear magnification.
One can just imagine how much hard physical work he put in to grinding concave lenses by hand. We see the breakthrough, but it’s easy to underestimate the tedious hours he must have spent grinding away, and the many failures he would have thrown in the bin before he got it right.
His mother wanted him to quit school and go to work on the family farm in order to support her. Fortunately for history, Newton’s schoolmaster was able to change her mind.