Ah mates... that's the thing! The quality... DO stands for Diffractive Optics, which is the name for this new technology that Canon is indulging in...
If you all might recall, the first DO lens was the 400 f4 L DO IS... what was outstanding about it was that the magic glass within the lens wasn't the usual L type.
L type glass consists of 2 kinds, UD ( and super UD) and fluorite lenses. Fluorite has a very unique refractive index. It maintains the colour integrity and unison of the light rays passing through it. UD lenses contain fluorite elements, and while do not achieve the same level of optical clarity, are far better than normal glass nonetheless.
Nikon's better glasses are made the same way.
Now, Diffractive Optics makes use of ordinary glass to produce the same if not better results than UD and fluoride elements. It does this by cutting steps into a lens ( like staircase u noe, steps?) and then sandwiching those steps inbetween 2 layers of glass. Now we're all familiar with how light disperses into its colours when it passes thorugh a prism. What these steps do is to unify the colours that are split through the previous lenses. IN a sense, its like the lens has an auto correction element.
Is this technology or wat? Of course, the cost of developing an element like that, with about like 1/1000 mm steps in the glass would of course cost about something like a pure fluorite element,... which haha,brings us back to the same cost...
Boh liao lar, photoshop can liaos...
........ hmmm... what's that ..... ahhhhhhhh .... hole in pocket 
