I would be interested to hear (read) the opinions and experiences of fellow Spherical Panorama Photographers on the subject of the number of images for a panorama, if they are prepared to share it.
I have read through Nick’s topic “How to choose a detent interval (shooting interval) updated” and followed the link to Frank’s calculator: www.frankvanderpol.nl/fov_pan_calc.htm
and noticed that the default overlap value is 25%.
I appreciate that the overlap value is a starting point as the overlap increases as we move away from the “equator” of the images.
The reason for my interest in this topic is that when I started taking panoramas back in the early 1970s I drew on my experience with photogrammetry where we used a 60% overlap when taking aerial photographs with the big 230mm x 230mm format cameras. This gave a 10% overlap between every other photograph and we would place our Ground Control (ground truth) points in this area. This lead to my using approximately a 50% overlap for my panoramas and I used the technique of taking my first photograph to the extreme left of the panorama, noting the subject at the centre and rotating the camera clockwise until this subject was against the left edge of the frame, taking the next photograph and repeating this process until I reached the right hand end, giving an overlap between each photograph of 45% to 50%..
Having this large overlap made the putting together of the panorama a lot easier as I used the same technique as making mosaics from aerial photographs by tearing the prints along a suitable feature to “feather” the edge. Provided that you did not look too closely, this gave great results.
Then I saw a spherical panorama on the Internet and wanted to achieve this myself. At that time surfing the net did not produce a lot of information and about the only thing that seemed to come from this research was the need for a fisheye lens, which I now know not to be true, but I eventually saved my pennies (cents) and purchased one and started experimenting.
I deliberately chose a “difficult” subject on the basis that it is not always possible to revisit the site if things were not right the first time and since then I have become involved with panoramas for introducing colours into HDS (High Definition Surveying) scans where the camera must be centred at the same point as the scanner so once the tripod has been moved on it is impossible to retake any photographs.
The results of my experiments, and previous experience with panoramas, has tended to produce much better results with overlaps of 45% to 50%, so I tend to take 8 horizontal images plus 2 nadir images with a Sigma 8mm or Nikon 10.5mm lens on a camera with an APS-C sensor. I found that using PTGui, 4 horizontal images required a lot of Control Point editing to get a sort of respectable solution and 6 horizontal images gave a better solution, but still needed Control point editing, whereas the 8 horizontal images processed sweetly. I also found that too many images (e.g. 12 horizontal images) created a problem as Control Points then appeared where they should not, and the only way to get a solution was to split the 12 images into 2 sets of 6.
I have also experimented with other lenses, such as the Sigma 10-20mm, and found that I get much better results using the bigger overlaps.
When it comes to the fisheye lenses it is clear that much less lens distortion has to be dealt with by using more images because of the way the no parallax point, nodal point, entrance pupil, centre of perspective, apparent pupil, or whatever you wish to call it, moves towards the front of the lens as the angle of view increases and that if 8 horizontal images are taken with a lens such as the Sigma 8mm or Nikon 10.5mm that this point coincides well with the gold ring around the centre of the overlap.
However, I find that when I look at the suggested number of images for a Spherical Panorama with a particular lens or camera that they are always much less than what I would use. For me, more is less (i.e. more shots in the field mean much less time on the computer), but I am wondering what others think.