sebboh wrote:
Jon Tainton wrote
edwardkaraa wrote
AhamB wrote
^Probably just pressed into a mold (which is why you see the "onion ring" artifacts sometimes). If I remember correctly, they don't have one specific way, but they choose the most suitable method according to design and price point. Also, as far as I know, it's not the molding that causes the onion rings, it's the milling/polishing of the surface. Non molded aspherical elements can also cause onion rings. Thanks, my limited searches had thrown up precision grinding/maching of glass, pressure moulding, and numerous fora discussions/speculations of glass and/or polymer materials etc.
I'm surprised it isn't disclosed though, as other manufacturers seem willing to disclose how their aspheric lenses are manufactured. zeiss uses molded aspherics, hand ground aspherics are easy to spot by price. the leica 35/1.4 with hand ground aspherics sells for over $10k and the one with molded sells for $3k. the nikon 58/1.2 with hand ground aspherics sells for $3.5k while the brand new 58/1.4 with molded aspherics sells for $1.6k.
hand ground aspherics cannot really be mass produced, which means the lenses they go in are collectors items.
If I'm not mistaken, most top quality aspherics are machine milled/ground by computer controlled platforms. They are much better quality than both molding and hand grinding, and much more economical to produce than hand grinding. In fact, hand grinding is a marketing gimmick, most elements are machine ground, and finished by hand in the last step.