I have just seen this on the Kowa website - http://www.kowa-prominar.com/new/telephoto101103.htm
A lens 'body' that can be converted into a 300mm, 500mm or 850mm by the use of adaptors with mounts from Nikon, Canon, etc. In addition, there is soon to be an adaptor that will convert into a telescope - though there does not appear to any indication of what magnification it will be.
The lens has a 95mm objective lens so should be bright. There are some test images here - http://www.flickr.com/photos/7892550...7625881842899/