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| p.4 #15 · Zeiss 100F2 vs Canon 85F1.2 |
Although not strictly on-topic, some clarification about glass types is in order here.
Lead isn't necessarily optically superior to modern lead-free substitutes (usually a lanthanide or other "rare earth" element). There's a tendency to think that because lead was phased out because of environmental concerns, there must have been something optically "special" about it. People incorrectly infer that because something is no longer available, it must have been especially desirable.
Lead's optical purpose is to increase the refractive index in the glass, which permits the design of lower curvature lenses (I would use the word "elements" here, but to avoid confusion with chemical elements, I will instead use "lenses" to refer to individual optical elements). This decrease in curvature reduces spherical aberration, but increases dispersion. So it's not a win-win scenario to employ high refractive index materials.
Furthermore, lead isn't the only element that can be used to increase the refractive index--for historical and geological reasons, it just happened to be the cheapest and most easily accessible one. People have been manufacturing leaded glassware for centuries. But it isn't intrinsically better from an optical perspective.
So let me make this absolutely clear: just because a lens is redesigned to phase out lead, does not mean the new design is inferior or constitutes a compromise in optical performance. It may, however, be more expensive to produce.
As for low-dispersion glass, of course Canon has that at their disposal. They just don't call it "ED" like Nikon does. Every lens manufacturer has an arsenal of glass types they can use, with a variety of refractive indices, transmissions, and thermal, chemical, and mechanical properties. The appropriate glass is chosen not just for its optical properties but for these other attributes. Canon calls their low-dispersion glasses "UD" and "Super UD," which are used in L lenses along with their trump card, pure fluorite crystal--which no other SLR lens manufacturer makes. In fact, a significant portion of Canon Optron's operations is devoted to the growth of these crystals, which are sold to other industries as well as used for Canon's own lenses.
In any case, these extra-low dispersion glasses aren't usually needed in short focal length lenses, because they have a low refractive index whereas a high refractive index is desired. An ultra-fast short telephoto like the 85/1.2 design has no use for this type of glass.