After clicking "OK", I get this dialog box. Since I checked the "Attempt to Automatically Arrange Source Images" option, Photomerge arranged the images as best as it can automatically. I get a preview of what Photomerge will do with the source images when I click "OK." I am going to keep the default settings, "Normal" selected and "Snap to Image" checked.




If I go up to the Navigator section of this dialog box in the upper-right, I can increase or decrease the zoom in the preview box. I dragged the slider to zoom in on the preview to get a better view.



There's a nice feature of Photomerge, called "Advanced Blending." It helps to match the exposure and colors of each image and blend them together to get a seamless, even "stitch." I am going to enable that feature by checking "Advanced Blending" under "Composition Settings." Then I am going to click the "Preview" button to get a preview of how well this blending will work.



This is a preview of what the panorama will look like with "Advanced Blending" enabled. Notice the diagonal lines are blended in better. The diagonal line on the left of the middle shot is completely blended in now. I think the height of the middle shot might have been a little lower than the 2 shots on the sides. This is definitely what I want, so I will leave "Advanced Blending" checked and click "Exit Preview" to exit the "Advanced Blending" preview.



Ok, we are back to the main preview area. I would have clicked "OK" to proceed and start the Photomerge while in the "Advanced Blending" preview, but I want to emphasize something that you shouldn't do here.