Besides the fact that the Sony A7s was proclaimed as the “low-light king” and became one of the most popular mirorrless compact cameras of 2014, it still has flaws.
Sure, it features a professional gamma curve such as S-log2, shoots 4K (though externally), has a full-frame sensor and Super 35 mm Crop Mode with full sensor readout (less moire and aliasing), 14 stops of dynamic range, 50mbps XAVC-S on-board codec, and incredible low-light sensitivity.
This is a whole set of highly demanded features by many filmmakers packed into a small compact body.
On the other hand, it has terrible rolling shutter issues (especially while shooting in Full Frame), you can’t shoot in daylight in S-log2 without heavy ND filtration (minimum ISO in S-log2 PP7 mode is 3,200), slow auto focus system, lack of internal 4K recording and some more considerable issues that we’ll find out in the next video test.
a7S Noise and Color comparison from Espionage Films on Vimeo.
The test was conducted by a Los Angeles-based cinematographer David Carstens. His initial aim was to fully compare the limits of capturing S-log2 internally with the Sony a7S. One of the main conclusions he makes is that when exposing a certain scene differently with a couple of stops under or over the correct exposure, a visible colour shift occurs while shooting in S-log2.
The shift is towards green
when the image is overexposed and towards magenta
when it is underexposed. Further, a snow-like noise appears while the image is underexposed. This is a good reason not to underexpose the image while shooting in S-Log2 mode in order to avoid the appearance of noise.
He also tried and managed successfully to match the colours form the different exposures in S-log2 with a Macbeth Chart in DaVinci Resolve 11. He used the chart as a control for the third sections of each picture profile, but loading the chart information did not achieve the results in terms of matching separate profiles to each other. However, he still found the chart match useful within individual profile sections as a control to observe chroma noise only.
There is another issue reported by some users of the camera where a lot of blue clipping occurs in a certain lighting situations that definitely ruins the image and makes it pretty unusable.
A7s color clipping issue from Kristoffer Davidsson on Vimeo.
The above material was filmed with Sony A7s, S-log2, Metabones Speedbooster, Tamron 24-70. The footage is straight from the camera.
Similar tests could give us more useful information about how to use the camera properly in certain shooting situations and how to avoid potential issues. They also reveal more of the weaknesses of each camera system that as filmmakers we should be aware of, especially if we tend to use camera such as the A7s for professional work or want to own one at some point.