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03-05-2008, 06:38 PM   #1
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What is difference "APO" and "ED" glass in a lens?

Is one definitely better than the other, or are there other possibly more important considerations in the lens?

03-05-2008, 07:07 PM   #2
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ED and APO is exactly the same thing: special glass design to reduce chromatic abberation. Nikon came up with the "ED" term 1st. Pentax and Olympus followed suit, while other manufacturers came up with their own term (Canon-LD, Minolta-APO, etc.).
03-05-2008, 07:17 PM   #3
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I believe APO stands for aprocromatic lenses, i.e. lenses that have allignment of all 3 colors at more than one point (focus point)

ED glass, is extra low dispersion (low refractive index) glass, that helps achieve aprocromatic lenses
03-05-2008, 07:18 PM   #4
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ED is low-dispersion glass. Using ED glass for some of the optical elements in particular in tele-lenses help minimize color aberration.

03-06-2008, 08:59 AM   #5
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QuoteOriginally posted by Lowell Goudge Quote
I believe APO stands for aprocromatic lenses, i.e. lenses that have allignment of all 3 colors at more than one point (focus point)

ED glass, is extra low dispersion (low refractive index) glass, that helps achieve aprocromatic lenses
Correct: APO stands for apochromatic lenses, and should should allign at least three colors (Blue, green, red) into the same point to prevent halo's around points or lines with big contrast. This is not the same as achromatic lenses, which only allign for two colors (Blue and red.) All lenses made these days are achromatic (or at least, they should be), but only some lenses (mostly the expensive ones and mostly telephotolenses) are apochromatic.

Note that apochromatic isn't the same for all brands: a Sigma APO lens would not be called apochromatic according to Leitz...

As for ED: that stands for extra low dispersion glass, which is used to help reduce chromatic abbarations...
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