Above is how the footprint of the 8mm Sigma Fisheye relates to different sensor sizes. Below is my home-brew no-parallax-point (NPP) adapter. It aligns the rotation axis of the rotator with the NPP of the camera.
Ever since I started using an APS-C sensor dSLR camera with an 8mm fisheye lens to create full spherical panoramas, I’ve used a slanted pano head.
There are several advantages to a slanted pano head compared to a traditional one. The key advantage for me was a bigger overlap which allowed me to either produce a sphere with three shots only; or to quickly take six shots around and easily mask out moving objects at the seams.
Moreover, the edges of fisheye lenses are softer than the center, and such a setup should use more of the center and less of the edge. Or does it? A discussion triggered my curiosity.
I needed a method to visualize the contribution of each shot to the final panorama, without influencing the seam placement. Bruno Postle suggested to desaturate the images and colorize them. This method does not change the artefacts which determine seam placement. I used it once on a still scene with constant artefacts and once on a moving scene. In this article I present the results for the still scene.
Below are the six input pictures that were fed to the different contenders for warping and blending:
Enblend did quite regular slices out of the images, taking mostly the central part of them, where the lens quality is at its best.
PTgui 8beta5 has an interesting and more complex / less predictable blending pattern. It seems that all images available contributed to the zenith, and that even around the horizon the boundaries are not at regular intervals. More in depth analysis would be required to understand the pattern.
Smartblend 1.2.5 in PTgui yielded a result similar to Enblend, again slicing the images more or less regularly.
Interestingly, Smartblend inside Autopano Pro display a slightly different placement of the seams while still keeping them regularly distributed.
For still scenes, unless the blender used is the newest PTgui one, the logic seems to hold true that only the central, sharpest part of the image is used.
And here is the finished full spherical panorama, interactive and in its original color.