Well...I am an L-Lens aholic...but not adverse to other manufacturers. (have two Sigmas and a Zeiss)....and I have no real call for circular images on my FF camera. I own the Canon 15mm Fisheye..I bought mine just before they were discontinued (why did Canon make that choice?), to make way for the 8-15mm, and although it is one of the oldest lenses in the Canon lineup I find mine to be small, sharp and a lot of fun. I researched the Sigma, and my readings told me that the Canon was sharper, built better and had no focus issues, better multi coating, and less flare which comes into play a lot with a fisheye...so I bought the Canon. I considered the 8-15mm, but the COST, the size and the slower f/stop and super-exposed front element just deterred me from buying that lens for a field of view I use occasionally when it is just right. (I thought it would be fun to have the circular, "novelty" option but resisted!!! LOL!). The Canon can stays tucked in my bag with its small footprint and can be on the ready when that fleeting opportunity arrises. Great little lens..I even like the whirring of the non-USM...kind of a cool photo quirk!!!!!