The leap in visual fidelity between series 6 and 7 of Doctor Who is pretty wild. Both series 5 and 6 look pretty similar on a technical level, I have a feeling they were shot on the same equipment, which produces very TV-looking images caked in digital noise. Exactly what you'd expect from an early HDTV camera in 2010-2011. But then in 2012/2013 they must have gotten new equipment because the digital noise of those first two HD series is basically gone and the whole thing looks much more "filmic" for lack of a better term. A lot of that part is probably down to the cinematographer, of course, but maybe the cinematography crew couldn't get as visually and technically creative until they got those new cameras in that brought all the other benefits. Since then DW has always looked Crisp and Sharp and almost noise-free. Just interesting to compare and see how the production of the show has evolved since 2005.