2 aspherical, 5 super low dispersion, 2 fluorite-like dispersion
[Tested on Canon variant]
It is an excellent lens in many ways, but probably not one that will make it into my bag. It is too large to be just a “bring along” lens [...]. The build quality feels excellent [...], but the lack of any weather sealing is a serious shortcoming [...]. If you need great low light performance in a wide angle lens for events or wedding work, it is hard to think of a better alternative. The resolution from the lens is fantastic.