The Lensbaby Fisheye optic for the Composer and Muse (with adapter) is a 12mm focal length, 160 degree circular fisheye lens. See the full review in a longer article.
I’ve been shooting with it on my Canon 350D which is converted for infrared photography with an internal 715nm filter.
Since the 350D is a smaller sensor dSLR, rather than a circular fisheye look we get an almost full image coverage.
While Lensbaby recommend leaving the fisheye centered on the lens and not tilted, I found some images were really enhanced by exploiting the fact that it is not going to cover the whole image anyway, so you might as well make it a feature and enjoy it.
There was no hotspot and the lens has now become a regular part of my IR kit.