Shortly after purchasing the Nikon 14-24 2.8 lens, I had second thoughts about the purchase. I was using the lens so infrequently that I wasn't even putting it in my camera bag for most outings. However, after more time passed and I became more experienced shooting from an ultra-wide perspective, the 14-24 became one of my favorite lenses. In fact, during my recent road trip from Chicago to the Pacific Coast, the 14-24 was my most frequently used lens!
Although the 14mm focal length certainly provides a very wide perspective when used with a full frame sensor, I'm finding many situations where an even wider perspective would be helpful--especially while shooting the interiors of many of the places of worship and state capitol buildings that I've visited.
So, I just ordered a Sigma 15m fisheye lens. This lens will provide an extremely wide perspective. The perspective is so wide that distortion will make keeping lines straight challenging or impossible at times.
Some have suggested that a better solution than purchasing a lens would be to stitch multiple exposures into a panoramic image to extend the scene. The issue that I have with the stitching approach is that I'm already blending 5 to 7 exposures to create a high dynamic range photograph as it is. If I were to then stitch three such images together, I'm now looking at 15 to 21 exposures to make a single photograph. Not only does that number of exposures add to the capture and processing time, but things tend to change within the scene over time--such as people entering or leaving the frame. Then, there's the issue of storing that many files on a regular basis.
I understand that getting good images from the fisheye lens will take practice. I hope that the experience I've gained over the past two years shooting at 14mm will accelerate my learning curve. I hope to be sharing some interesting fisheye photographs in the near future.