ED Cameras lens converted into a telescope?

Has anyone converted (or attempt to convert) a Nikon or Canon ED super
telephoto camera lens ( eg. 400mm F2.8, 500mm F4, 600mm F4, 800mm F5.6 or
1000mm 5.6) into a refractor telescope and attach an eyepiece for visual
use? If so, how do you increase the back focus so that a star diagonal can
be used? The back focus of these 35mm designed lenses are short. Will a
barlow lens increase this back focus distance and enables the use of a star
diagonal?
If it can be done, will the images equal or surpass the normal APO
refractors like Takahashi, tele Vue, etc? Any comments? Just thinking aloud.