I have a Soligor 450 mm lens with a 40 mm dia camera body end thread connection. I would like to try adapting it to a D90 AF system. Are there adapter rings available out there for this purpose?
Assuming it is an M42 lens as some research on the particular model suggests, M42 to F mount adapters are readily available.
But since the M42 register is shorter than the Nikon one, you'll have to choose between two types of adapters: those which do not preserve infinity focus (by being indeed short extension tubes) and those who compensate with a generally poor quality element. In this peculiar case, with the difference being barely over 1 mm, some adapters without extra glass allegedly capable of infinity focus exist, but keep in mind the manufacturing tolerances on such cheap items are often too relaxed for being a critical component of the optical path.
As already stated by Evaldas, none of them will enable autofocus, especially since this lens has a minimum aperture of ƒ:8 and Nikon only guarantees operation of the AF (and focusing assist) system at apertures larger than ƒ:5.6.
As already explained, M42 screw-mount lenses won't focus to infinity on F-mount bodies (Nikon and some Fujifilm SLRs) due to negative difference in lens-mount register distance.
But, since you're trying to use long telephoto lens, you would get working infinity focus, regardless of inherent mount incompatibility - long-focal lenses usually focus past infinity mark enough for smaller register difference. Since register difference between M42 screw-mount and F-mount is 1mm (45.46mm vs. 46.5mm), 450mm lens would probably focus to infinify just fine.