stic wrote:there is still a misalignment at the bottom of the image
I can't tell if the screenshot you posted is of PTAssembler's preview or a final blended image. I suspect that it is probably a screenshot of the preview, in which case I wouldn't worry too much about that misalignment...the preview doesn't do any blending (in order to speed up the preview), so minor misalignments between the images are often visible. In practice, these types of misalignments are usually removed when a final blended panorama is created due to the "intelligent" blending algorithms implemented in blenders like Smartblend and Enblend.
If the misalignment is visible in the final image, then either the images aren't well aligned or there are enough people and other objects moving around in the images that seamless blending is impossible regardless of how well aligned the images are. I don't think this is the case for your panorama, but regardless of this, here are two things that you can try to improve the image alignment:
1. To the extent feasible, place control points along the entire length of the overlap area, rather than clustering them in one region (your project already looks pretty good in this respect, but adding two or three more points might be helpful). Try optimizing again after adding a couple more points.
2. Try adding FOV and perhaps the d/e parameters to the list of variables that are optimized. Even though PTAssembler was able to calculate the FOV from the EXIF data, the EXIF data is usually only approximate, and you can finetune the FOV value by optimizing it. Also, most lenses aren't perfectly centered, so I find that optimizing the d/e can also help improve the results slightly. Add these variables (by checking the appropriate boxes on the step 4 screen), and then optimize manually. Keep an eye on the results; if you find that the FOV has changed a lot (i.e. by more than 20% or 30%), then chances are that the optimized FOV isn't an improvement after all, and you shouldn't accept the change.
How can I maximize the size of the preview image within the preview window?...most of the preview window is empty space
Short Answer: Decrease the Horizontal and/or Vertical FOV values, and press the "Re-Draw" button.
Long Answer: The preview window always shows the point where yaw=0 and pitch=0 at the center of the screen (the intersection of the red and blue lines). Changing the horizontal and vertical FOV values changes how much angular field of view is shown above/below and left/right of this point. If you check the "Yaw/Pitch" checkbox, you'll see a grid superimposed on the preview showing lines that indicate 10 degree increments that may help make this more understandable.
Anyway...you should be able to get an excellent result with these images. I added a few more control points, optimized the project again after including FOV and d/e, and then created the result below (using rectilindrical projection to reduce the amount of stretching along the vertical axis):
The alignment is really good. Here is a crop from the bottom of the pano where the images overlap...the blender (Smartblend in this case) has done a nice job of routing the seam to avoid the moving people, and hides any residual minor misaligments. Note that the ghosted child is present in the original image...it isn't an artifact of the blending.
Lastly...here is the project file
after my changes.
Hope this helps,