If the aim is to get shallow DOF, you need fast glass to achieve it... I have tried D5100 for video, but I ended up investing on NEX mount cameras (VG20/30) that I found superior... Still, being in a similar situation (because of the APSc size sensor) and since I have a huge collection of Nikkor lenses which I use with my FF cameras, I use the Sonys with Nikkor glass using adapters in MF only. My favorites for video are the 14mm f2.8D, the 17-35mm f2.8D, the fisheye 16mm f2.8 AI-s, the 24mm f2 AI-s, the 28mm f2 AI-s, the 35mm f1.4 Samyang, the 50mm F1.4 AI-s, the 85mm f1.8D, the 28-70mm f2.8D and the 80-200mm f2.8D dual ring. Notice that all the above are FF lenses and all of them have aperture rings... I have also tried the 17-55 f2.8 G which can be sharp at full aperture for video, but dropped it in favor of the even sharper 17-35 due to the lack of aperture ring. Also, I have this opinion that proper video is MF only... You can't have (other than the poor AF performance and noise) the focus depth changing all the time... no?