For cheap glass with big error bars on refractive index, dispersion, and defects, the process is entirely automated - think window glass or beer bottles. Quality control is still hard, and a lot gets recycled as cullet or discarded, but that isn't too much of a problem, since it's cheap. When you're working at that sort of scale, the furnace/melt behavior tends to be quite predictable and stable as well. Once you've dialed it in, it's good for quite a bit.
For such small batches of glass (500kgs is nothing!) with very tight tolerances across lots of variables, and considerable compositional diversity (Nikon isn't melting just one glass, it's melting quite a few, to do clever things with dispersion), there are so many variables that you can't really automate everything.
(As a glass melting nerd, I'd really love to see all of the proprietary information that they left out - but I guess that's why it isn't there.)
Entirely automated - if it's glass, big, flat, and smooth, it was almost certainly made via the float glass process, or an equivalently automated continuous-flow system.
Sliding glass doors are typically one or two panes of hardened 'float' glass. I put the 'float' between quotes because these days hardly anybody makes float glass by floating molten glass on plates covered with molten tin but instead the glass is cast continuously between rollers. The cooling regime has a large effect on hardness (as does composition), and for extra strength there are other tricks such as lamination.
A couple of years ago I was at Leica's booth at NAB talking to a rep about one of their Sumicron-C lenses. For the nominal fee of $100,000.00US, they will make you a set of lenses by hand. Of course, it takes 18-24 months to make them. For an additional $75,000.00US, they will nearly double the number of lenses in the kit. Apparently, if there is the slightest defect in the glass, they do not attempt to polish/grind it. They simply crush it and start with a new one. Hand made seems to be the way it's done. Maybe they have already learned what Tesla is learning. Automation is not always the best way.
Not to rain on Leica too much (I love and had a whole M system) but I experienced some serious backfocus issues with their Summilux 50mm which despite two visits to their factory (which took two months) they were unable to fully rectify.
I’m not the only one, photographer Ming Thein has complained about the sample variation of Leica’s hand made lenses too.
The hand crafted nature of their range finder system is far from perfect and for the price it really should be better.
> It's interesting to see how manual the process still is.
This reminded me of a programme I saw a couple of years ago about making a perfect sphere. From what I can remember they said that was hand finished. I've just done a quick search and it looks like it would have been Achim Leistner making the 1Kg sphere.
Narration: The sphere started life as an ingot of pure silicon 28, brought here from Germany. Silicon crystal was chosen as the material because of its uniform atomic structure. The silicon ingot is cut and ground into a rough ball shape. Then Achim starts the painstaking process of transforming it into a near perfect sphere.
Achim Leistner: And this can only be done by hand because you actually have to feel what is happening. When you’re taking off a nanometre or 5 nanometres, or 10 nanometres or 20 nanometres, some of the errors we’re trying to correct are in the vicinity of only a few nanometres.
Narration: That’s a few billionths of a metre! If this sphere was the size of the earth, that accuracy would be equivalent to changes in height of only 4 or 5 metres over the entire surface of the planet. But that’s only half the challenge. To redefine the weight standard as a universal constant, the team also have to count the number of atoms in the sphere.
Japan still greatly values the "small scale, hand made" market to a degree effectively entirely lost in most of the rest of the world. https://www.youtube.com/watch?v=vYzQNgIwqgo was a great showcase of that, too.
As has already been suggested - high-end watches; Grand Seiko and Credor.
Fountain pens - Sailor, Nakaya, Namiki for instance.
Oh, and knives. Definitely knives.
In their higher end items, they tend to employ traditional craft techniques (zaratsu polishing; urushi lacquer to name but two) which are incredibly labour and skill intensive.
Oh, don’t knock the Seiko - Seiko is a true manufacture - they do EVERYTHING in-house - movements, cases, dials, mainsprings - even lubricants.
This in stark contrast to some of their Swiss, in general more prestigeous counterparts.
(Do yourself a favour and have a look at the Grand Seiko website - they have some quite interesting info on their craft techniques. Not to mention that it is watch porn squared.
I'm guessing this is the main reason lenses like the 600mm f/4 FL VR are $12,000+ (probably every element is handmade/inspected), while cheap plasticky lenses like the 18-55mm f/3.5-5.6 VR are $100 or so.
My guess is the cheap lenses are fully automated, using fewer actual glass components, without features like 'ED' glass which requires all these extra manual processes and firings.
There's a lot that separates a cheap 18-55mm kit lens from the super-expensive telephotos. But probably the single biggest factor is that the 600mm f/4 requires much more glass and in much larger pieces, so even with the same target for optical quality you would expect to have much lower yield and higher manufacturing costs for the massive telephoto than the pocket sized kit lens.
It's probably more interesting to compare the differences between two lenses of similar focal length and aperture. With that kind of comparison, the kind of differences that you'll find are that the more expensive lenses tend to have metal instead of plastic frames, may have optical stabilization in the lens, fancier or faster autofocus systems, better sealing against water and dust, and more advanced coatings on the optical elements. In terms of the glass itself, you will also generally find that the more expensive lenses use more optical elements with potentially more complex shapes (eg. aspherical elements) to reduce distortion, so they tend to have more glass than the cheaper lenses. Given how many other factors contribute to the price differences, I doubt that you actually find order of magnitude differences in the price of unground lens blanks of similar size destined for cheap vs high-end camera lenses.
Nikon seems to have moved a lot of their high-end manufacturing to Thailand. The D810 body is the first "pro spec" Nikon body with the circular viewfinder to be built overseas AFAIK.
They still have two plants in Japan where high-spec lenses and bodies are built. I think the criteria is "how hard is it for us to build", not ED (etc.) glass: The new 105mm f/1.4 and 200-500mm f/5.6 both have a lot of ED glass but are made in China.
There is still enough demand and value attached to "made in Japan" for Cosina to make vintage throwback "Voigtlander" lenses in Japan, and for Converse to make high-quality Chuck Taylor sneakers there.
I would've thought for something like manufacturing glass, you would be able to make the process more or less entirely automated.