It’s low light ability is definitely key. While some videographers chose to use video lights these can be unobtrusive and cause people to turn towards the camera. A light straight in the face is also not a flattering light so unless you have time for a proper lighting setup (which you don’t at weddings) natural light is the best option. The a7sII is the top performer in low light with low noise images up to 20000 ISO and a staggering if a little grainy 409600 at the top end, quite good for capturing the atmosphere around a sparkler shot.
In addition to low light capabilities what really sets it apart from other DSLRs is its stabilisation. With my old Canon 60D you would not even think about using it hand held however the a7sII has in-camera stabilisation which really helps the images look smoother. Shaky DSLR footage was trendy especially on the streets of Shoreditch in 2011 but no one wants to see all that wibble wobble now. That said I still use a monopod most of the day if only to save my back.
The major limitation is that the audio recording options are not up to the pro level required for wedding videography. I use a separate sound recorder to overcome this. This may not be practical for all types of filmmaking but in wedding videography works perfectly and even adds an extra fail safe of an extra audio source being recorded.
Ok the a7sII is the best DSLR for videography but why are you using a DSLR at all you may ask? Well even if you look at top of the range pro video cameras they still don’t have the low light ability of the a7sII and they are also more obviously video cameras. It’s actually useful to pretend you are preparing to take a photo when you are actually filming someone. They are also lighter enabling you to move quicker and get more shots.
DSLRs have been have been popular for several years because of their cinematic quality which exceeded that of most traditional video cameras. This was primarily because of their large senor and interchangeable lenses which gave the look of a 35mm film camera. There did however have problems; the mentioned shakiness, audio and rolling shutter. Traditional video cameras have got better and new interchangeable lens video cameras such as the C100 and C300 have made many people send their DLSR’s into video retirement. That was before the a7sII came along.
Of course there are cinema cameras which will produce better images but in my opinion you will struggle to notice any real difference to the a7sII unless you project on the big screen and with a pro-cine camera like the Arri Alexa or the Red Epic you may get a few great shots at a wedding but only a few shots as they are trickier to use and require a professional lighting setup to really make them sing.
I was once asked to make someones wedding video look like Breaking Bad. I’m assuming and hoping they were referring to the cinematic quality and if so it would have been achieved with a cinema camera and a large team of people lighting the set. Not realistic in your wedding video sorry, not even if you are Will and Kate.
For more examples of the a7sII in action please see my wedding videography page.