Who is the Artist?

This link will bring you to a Flickr page showing five book covers. These are all from a set of Arthur C. Clarke books that Ballantine came out with in the 1970's (Childhood's End, Earthlight, Reach for Tomorrow, Expedition to Earth and Tales from the 'White Hart').

Can anybody identify the artist? One suggestion was that it was Dean Ellis (who did do the same set of Clarke books several years later), another suggestion was Vincent Di Fate; but we can't be sure.