I am doing a physics project on why fluorite is used in Canon\'s high performance super-telephoto lenses but I need to clarify somethings before I write it up.
1. Is fluorite an aspherical element and are they connected in any way?
2. Can someone explain extraordinary partial dispersion to me, I looked on canon\'s EF Lens III pdf and couldn\'t understand exactly what it meant?
3. Are DO elements made of fluorite?
4. Is the fluorite used in Canon\'s S T Lenses CaF2, and if so will the atomic structure I find on wikipedia and such be identical to that of the crystals that Canon implement in their elements?
Please help,
Fred
1. it has nothing to do with aspherical or not (i\'m pretty sure they could never make a molded aspherical and obviously not resin replica aspherical perhaps they could make a carved/polished type which is the costliest sort but I don\'t think anyone makes aspherical fluorite elements, i\'m sure it\'s far easier and cost effective to put those on different elements in teh designs where they may make more sense to be placed anyway)
2. you can find all sorts of info on this all over
do a little google, look at Optics by Hecht for a little more
but anyway putting it really simply fluorite doesn\'t disperse visible wavelengths of light as much as glass for some visible wavelenghts so it can focus all the different wavelengths closer to the same spot while leaving others farther out and if they have used regular glass in pairs to bring parts together fluorite can bring back the part they left far out while not much further dispersing the parts they already brought together, i.e. less CA fringing in the end; some simple focal lengths they can just use regular glass like in a 50mm and mirror the dispersions to cancel them out
3. no, DO has nothing remotely to do with fluorite, they are diffrative optical elements, although some DO lenses do also have fluorite elements
4. yes. I think Canon may still be the only company (hmm could be wrong actually), anyway certainly the only DSLR maker, that can grow their own pure, large fluorite crystals, Nikon fluorite elements are not pure crystals but glass doped with a lot of fluorite.
I am doing a physics project on why fluorite is used in Canon\'s high performance super-telephoto lenses but I need to clarify somethings before I write it up.
1. Is fluorite an aspherical element and are they connected in any way?
2. Can someone explain extraordinary partial dispersion to me, I looked on canon\'s EF Lens III pdf and couldn\'t understand exactly what it meant?
3. Are DO elements made of fluorite?
4. Is the fluorite used in Canon\'s S T Lenses CaF2, and if so will the atomic structure I find on wikipedia and such be identical to that of the crystals that Canon implement in their elements?
Please help,
Fred
1. it has nothing to do with aspherical or not (i\'m pretty sure they could never make a molded aspherical and obviously not resin replica aspherical perhaps they could make a carved/polished type which is the costliest sort but I don\'t think anyone makes aspherical fluorite elements, i\'m sure it\'s far easier and cost effective to put those on different elements in teh designs where they may make more sense to be placed anyway)
2. you can find all sorts of info on this all over
do a little google, look at Optics by Hecht for a little more
but anyway putting it really simply fluorite doesn\'t disperse visible wavelengths of light as much as glass so it can focus all the different wavelengths closer to the same spot, i.e. less CA fringing in the end; some simple focal lengths they can just use regular glass like ina 50mm and mirror the dispersions to cancel them out
3. no, DO has nothing remotely to do with fluorite, they are diffrative optical elements, although some DO lenses do also have fluorite elements
4. yes. I think Canon may still be the only company (hmm could be wrong actually), anyway certainly the only DSLR maker, that can grow their own pure, large fluorite crystals, Nikon fluorite elements are not pure crystals but glass doped with a lot of fluorite.
Nov 08, 2009 at 04:05 PM
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