|One of the things that people complain about
with film scans from circular fisheye lenses is the increased amount of
grain (noise), particularly in the sky. Increasing the number of images used
(and thus the amount of image overlap) does not solve the problem... and
this is because the amount of horizontal overlap has very little to do with
the zenith or nadir. Note that this problem also applies to images from
digital cameras, although the amount of noise is usually lower.
With a single row of fisheye images of 180°, the zenith and nadir will
always be at the edge of the image. Increasing the number of horizontal
images improves the image quality around the centre of the panorama, but not
at the top and bottom.
illustrate this let's take an image that
consists of concentric coloured circles with a grid of 1 pixel black squares
representing image noise.. The black circle represents the image circle of a
fisheye lens with an FOV of 180°. When the image is remapped to an
equirectangular projection the portions of the image near the edges get
distorted more than those near the centre.
the FOV is 180°, remapping this to an equirectangular projection will create
a square. The test image below uses the same distortion settings for my
Sigma lens (a-0.2 b0.3 c-0.2)