The third regeneration, from the the third Doctor (Jon Pertwee) to the fourth (Tom Baker), was disappointing, to say the least, even taking into account the special-effects restrictions of the time. I've updated the transformation here, with a morphing effect, but note how the lighting changes between the last scene of "Planet of Spiders" and the UNIT lab scene in "Robot". Also, not only does Sarah's hair famously grow (an effect of being close to the Doctor's regenerative energy, perhaps?), but someone (who?) has closed the TARDIS door!