For those who think there isn't much difference in focal lengths in the UWA range I present these pics in evidence. These pictures were taken 3 years apart (almost to the day) with 2 different cameras mounting two different lenses. Obviously there's some slop because of the variation in equipment, but the pics still illustrate the point. The POV is slightly different as I hand held the 10mm shot and the 12mm shot was from the tripod approximately 18" closer to earth. First up is the older shot, taken with my Pentax K20/Sigma 10-20 @ 10mm. And the newer one taken with the 5N/CV12 3 weeks ago. Notice that in the first shot I am standing inside the short wall, probably nearly touching the bench mounted to the inside. To get a similar fov with the CV I had to go outside the wall. Difference in distance from the boulder is about 8 feet or so (I didn't measure). If that wall were 5 feet tall instead of 2 feet tall I would not have been able to get the shot with the CV without stitching shots. As you can see, small difference in focal length for UWA can make a huge difference in getting or not getting the shot. And wow, that white balance in the first shot is really messed up. I need to go back and fix that.