Stitching images

The following image is a series of images stitched together in Photoshop.  

When taking a series to be stitched, you want to have a reference point that you can keep consistent.  There are two ways to do this.  For a distance shot, it can be the position of the horizon.  This series of photos were to take a close up panorama as a wide angle so the horizon was maintained at the top third.  The better you are at keeping that focus consistent, the better that the stitching software can do to find the overlap points.

What I did 'wrong' with this image is that I didn't force a manual exposure.  The blend line in the middle is due to the camera adjusting the exposure automatically as I moved the camera for the next shot.