To obtain nice panoramic renderings, up to a full 360° view of the horizon, Blender provides an automatic procedure.
If the Xparts is greater than 1 and the Panorama button is pressed (Figure 5), then the rendered image is created to be Xparts x SizeX wide and SizeY high, rendering each part by rotating the camera as far as necessary to obtain seamless images.
Figure 6 shows a test set up with 12 spheres surrounding a camera. By leaving the camera as it is, you obtain the rendering shown in Figure 7. By setting Xparts to 3 and selecting Panorama the result is an image three times wider showing one more full camera shot to the right and one full to the left (Figure 8).
To obtain something similar without the Panorama button, the only way is to decrease the camera focal length. For example Figure 9 shows a comparable view, obtained with a 7.0 focal length, equivalent to a very wide angle, or fish-eye, lens. Distortion is very evident.
To obtain a full 360° view some tweaking is necessary. It is known that a focal length of 16.0 corresponds to a viewing angle of 90°. Hence a panoramic render with 4 Xparts and a camera with a 16.0 lens yields a full 360° view, as that shown in Figure 10. This is grossly distorted, since a 16.0 lens is a wide angle lens, and distorts at the edges.
To have undistorted views the focal length should be around 35.0. Figure 11 shows the result for a panorama with 8 Xparts and a camera with a 38.5 lens, corresponding to a 45° viewing angle.
The image is much less distorted, but special attention must be given to proportion. The original image was 320x256 pixels. The panorama in Figure 10 is 4 x 320 wide. To keep this new panorama the same width, the SizeX of the image must be set to 160 so that 8 x 160 = 4 x 320. But the camera viewing angle width occurs for the largest dimension, so that, if SizeX is kept to 256 the image spans 45° vertically but less than that horizontally, so that the final result is not a 360° panorama unless SizeX ≥ SizeY or you are willing to make some tests.