I am using photoshop to stitch together 40 photos of the grand canyon I'd like to combine into a larger panorama. The photos are in Lightroom (Canon Raw files from a 5D mk ii). I highlight them and select the merge as panorama in photoshop option. I choose perspective combine (the first option). Once the photos are combined (a process that takes about 15 minutes), the horizon is very, very curved, and heavily distorted, as if the photo was taken with a fish eye lens (each individual frame is shot at 70mm). What is the best way to straighten the horizon and remove the distortion to make the photo appear natural? Lastly, I want to maintain the RAW info so that I can edit the photo to it's full potential in lightroom, however photoshop only lets me export hte panorama as a tiff or jpeg. What's the best way to retain as much information as possible in this scenario? Thank you all for your help.