Getting Wide with the canon 14mm
I just finished up my rental of the Canon 14mm 2.8 L for a weekend gig. I wanted to put it through the paces and see how wide 14mm looked on a full frame sensor. The first thing you notice is that this lens is going to give you lots of coverage. You can compose well in tight spaces and create some interest compositions It's not a fish eye, but it is pretty close, and this is certainly a concern when shooting people. I thought it would be fun for shooting a musical event covering the stage close.
When shooting people you can get incredibly close to your subject in order to fill the frame. This is where the distortion is most evident. This can be fine in some settings and entirely wrong in others ( i.e. it's not a portrait lens). I found it to work well shooting the performances for a short bit, but soon I longed for some zoom and I switched back to my 24-105mm to finish out the night.
Having also rented the Zeiss Distagon T* 15mm f/2.8 ZE lens in the past, and if I had to choose between the Canon 14mm & Zeiss 15mm, I would go with the Zeiss. I found it to have better color rendition and less distortion. It's a little heavier than the 14mm, but it's a Zeiss. In the end both are great for what they do, and remain great options for landscape photography, music, architecture and when working in tight spaces.