This was the first Canon wide angle interchangeable lens for SLR camera that had the floating mechanism in its optical system. The floating mechanism moves a part of the optical system separated from the focusing lens group to minimize fluctuation of aberrations caused by focusing distance change. A inverted telephoto lens type wide angle lens like this lens, having negative power like a concave lens for front lens group and positive power like a convex lens for rear lens group, tends to have more astigmatism at shorter focusing distance with more extension. The floating mechanism corrects this astigmatism well. This mechanism is named “floating”, because an optical part moves like a float, not in union with the rest of the focusing group. S.S.C., an abbreviation of Super Spectra Coating, is a coating technology developed by Canon to achieve harmonized color balance for all lenses.

This specific "Convave" "0" " SSC" version is the most sought after and claimed to be the sharpest lest ever made by Canon. Sources are within easily searchable videos on youtube and google.

The lens offered here has some historical and noticeable wear along the sides, but the glass elements remain free from any fungus or even dust. The mechanics are in good working order, I will however note that the focusing grease is older and you can feel it is showing signs of its age. I have not noticed the effects of the radioactive elements pose any issue.

Feel free to ask questions.