Earlier in the week, we shared a comparison of the dynamic range of the Sony a7S to a few other popular cameras, and the results were enlightening. It turns out that the combination of the massive pixels of the a7S sensor and the ability to shoot with an S-log2 gamma curve provides for some impressive dynamic range, to say the very least. Of course, we all know that no camera system is perfect, and the a7S is no exception, especially in regards to rolling shutter. In another comparative test from Cinema5D, they measured the effects of rolling shutter on a variety of popular CMOS cameras, and unfortunately, our beloved a7S didn't fare well at all.
First, here's a brief rundown of how the rolling shutter test was conducted:
On the left you can see a frame grab from the A7S video file used to determine its rolling shutter. We used a rotating test chart framed identically with all cameras. The amount of horizontal offset between the first and last line of pixels determines the severity of rolling shutter which we measured in milliseconds. These are approximate values (Precision is limited by our method of testing as it involves a slight amount of motion blur).
And here are the results from the Cinema5D rolling shutter test:
This is what the Cinema5D folks had to say about the results:
Our test results show that the A7S’ rolling shutter in full frame HD mode is severe, but we also found that the Canon 1D C performs similarly in 4K mode. Among DSLR style cameras in our test the GH4 in 4K mode performed best and is more or less on par with the A7S’ crop mode, and the 5D mark III coming in right behind that. As expected the ARRI AMIRA has an outstanding shutter readout speed almost looking like a global shutter.
Essentially, this test shows that the a7S is, in fact, highly susceptible to rolling shutter, especially when shooting in full frame mode -- which, let's face it -- is how most people use the camera. It's rather unfortunate considering that the camera exceeds expectations in many other areas like dynamic range and low-light ability. But again, there is no perfect camera.
Here's a quick example of the rolling shutter on the a7S, both before and after a "rolling shutter repair" effect has been applied:
Ultimately, the fact that the a7S suffers from severe rolling shutter isn't something that should necessarily deter anybody from using the camera, except in very specific situations such as frenetic handheld work and when objects need to move quickly through frame. Rolling shutter is something that most of us who have been shooting with DSLRs and non-global shutter cameras are accustomed to dealing with, and there are numerous workarounds, both in how you shoot and how you post-process the footage, that can alleviate some of nasty effects of rolling shutter.