Hi @bags,
A few thoughts to answer your questions.
- 30% overlap should be good. Just know that the more shots you try to stitch together, the more likely it is that you’ll run into issues getting it to stitch together. This is especially true in scenes that have lots of “empty” space, like sky. With 6 shots, you will be quite close to the image and may end up not having enough context in each frame for the software to find the right place to stitch. For medium format, my approach is typically to do just 2-shot stitches, which is an easy way to double resolution, and it will stitch very easily in Lightroom or anywhere else you try.
- PTGui will offer more options than Lightroom or Photoshop. And Photoshop will offer more options than Lightroom. Lightroom’s options are limited, but the biggest advantage of Lightroom is that the resulting stitch remains fully RAW, so you are not losing any of the underlying raw camera data and can just continue to work off it non-destructively. You can see more of my tips on pano merges in Lightroom here. If you plan on stitching together more than 2 frames, you might be better off doing it in Photoshop or PTGui.
- The most crucial part of getting this right is your camera scanning setup. First, you want to make sure that your camera is perfectly in plane with your film. You can use the mirror alignment trick to do this. Second, you want any movement of your film between shots to keep it perfectly in line with the previous shot… having a film carrier that lets you mechanically advance the frame is ideal… if you have to try to move your film by hand, it’s likely it won’t be perfectly parallel with the previous shot.
Hope that helps!
-Nate