Quote - Some of my panoramas have been blurry, though.  I'm not sure why.

Two factors come into play. One is the resolution of the panoramic image. I use images that are at least 6, 000 pixels wide, and often 10, 000 wide. Lower resolution images are liable to produce less detail.

The other factor is the field of view in your render. If you have a long focal length (telephoto) then your field of view may be only a few degrees. Say you have a field of view of about 5 degrees, and your panoramic image is 10,000 pixels wide - each horizontal line of your render will have 5/360 * 10,000 = 139 pixels of information from the panoramic image.

If you use a short focal length (wide angle) then you might have a field of view of, say, 20 degrees. 20/360 * 10, 000 = 556 pixels of information.

High resolution image + short focal length = sharp backgrounds

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