<p>Sorry about 5 yrs. too late to discussion here BUT - having owned 2 great copies of the 400 4.5 & 500 L have to state that the 400 is a great lens and DOES have 1 UD glass element in it and is very sharp. However it no way shape or form surpasses or comes close to the 500 L with UD AND Flourite elements. CA is almost non-existant and wide open {where most shoot these super-teles anyway] is as sharp as any lens ever produced in the FD line! { along w/ the 300 2.8 L that uses the same fluorite construction design} There is a reason the L lenses are priced in a different structure than the 'non-l' glasses, even in modern EF designs. The L lenses are made to combat the CA, diffraction , distortion, coma, etc. that the less expensive lenses have to some degree. I' ve owned all L glass at one point many years ago and after dealing w all the lenses from the line that they replaced, i.e. 20-35 L, 50 1.2 L, 85 1.2L, 300 4L, 500L the L lenses are TOP NOTCH for a reason. Some lenses in the FD line are suprb and didn't need L versions as there wasn't much to improve over the original. 35-105 two touch being one right off the top of my head. But Back to the point, the 400 4.5 whilst being a great lens is NOT an L lens by far and away!</p>
