When do aspherically ground lenses date from?

[Eric Woodbury]

The Schmidt corrector plate is an aspheric surface with a 'wave shape' cross-section. Originally used in some telescopes, it is now used for other applications. About 100 years old.

[Drew Wiley]

Well, I found at least one page of history intact at Tinsley's website. Tinsley Lab began as a local telescope manufacturer nearly a hundred years ago (1926); but due to their govt connection making artillery scopes during WWII, starting getting major space application contracts in the 60's, and have since merged into Coherent laser imaging (also local), and have also acquired Quantum coatings, overall now becoming the most significant space optics and major ground telescope supplier in the world as far as specialized elements are concerned, especially aspherics. I don't know if the virtual tour of that facility is still buried somewhere in the current site; but at least a few pictures are still there. It's just two Freeway exits from my house. Be fun to see in person; but all the real deal work is clean suit stuff, just like satellite making, so not open to public tours. But just perusing a site like that gives one an idea of the scale of what is necessary to a modern astro operation. And nowadays, things like aspheric mirrors have be made in precisely matching high multiples. Just spitting on the end of a Millers beer bottle and grinding away with it with some beach sand doesn't do it anymore.

The Schmidt telescope design dates from the 1930's. The 41 inch mirror for the well-known Kitt Peak Schmidt scope was made by Tinsley in 1960. But there are all kind of historic links showing just how darn big the mirrors many amateurs ordered from them were over years, plus a few of the huge teaching telescopes in this area.

[pgk]

That's the problem. I got interested in the Grubb's and their photographic lenses but it so easy to get sidetracked and I've ended up with many more related questions than I started with. And two Grubb telescopes too! One is an astronomic 3" but the other is a miltary scope and was never taken into miltary use. It took a lot of figuring out but seems to be a varaible power artillery spotting scope with a horizontal reticle with angular offsets for flash spotting. At 103 years old it is still very usable. The astronomic 'scope is earlier but has had a Barlow eyepiec by Dolland fitted not long after it was made - another photographic lens maker and for me a connection because when I was a student I worked for camera dealer R G Lewis in High Holborn, London which was then owned by Dollands. And yes, still looking into the Grubb photographic lenses which has revealed an interesting world of Victorian science and engineering. Makers like the Grubbs were extraordinarily competent. Howard not only built world class telescopes and numerous other scientific instruments but went on to create the basis of what is now referred to as the Red Dot Sight and built Periscopes for most British submarines used in WW1. And he made a fe photographic lenses as a bit of an aside too. Too easy to get diverted.

[Nodda Duma]

Polishing optical surfaces is as much craft / art as it is science and method. Before telescope making moved into proper shops, final polishing often took place at night under the stars, with the optician closely examining a star image and polishing away aberrations with their thumb. Alvan Clark finished off the world’s largest refractor (the 40” at Yerkes Observatory) that way.

I’ve tried this before, and it is doable but easy to overdo it and get poor surface irregularity as well as blowing through your intended goal and leaving a “hole” in your otherwise perfect surface.