A Filmmaker's Perspective

By Andrew Reid, EOSHD.com

Key points for filmmakers

The Sony a7S shoots the best looking internally captured 1080p video of any current mirrorless or DSLR camera. However, shooting 4K with the a7S is less ergonomic and less affordable compared to some of the competition. The Panasonic GH4, Samsung NX1 and Canon 1D C all have internal 4K recording, which is more convenient.

As a filmmaker I find the a7S has some great creative advantages over a number of other cameras, thanks to the 12MP full-frame sensor with stunning low light capabilities, adaptable mirrorless lens mount, and the built in EVF. Disadvantages include the lack of an internal 4K codec and the need to buy quite a few add-ons such as lens adapters, external recorders and battery grip to make up for the limited (and too expensive) E-mount lens range and poor battery life. I am not a fan of workarounds and they all add to the cost of the body!

That said, I very much enjoy shooting plain old 1080p with the a7S. If the a7S was a film look, it would be creamy and dreamy 65mm, as used to great effect by Christopher Nolan in Inception. By comparison the Panasonic GH4 has more of a documentary style, with fine grain and a similar feel to Super 16mm - The Hurt Locker springs to mind. Neither style is ‘right or wrong', they're just different. Subject/background separation is more abundant on the a7S at every focal length compared to APS-C or Micro Four Thirds. Shooting full-frame with the a7S allows for a three-dimensional-looking image even when the subject is at a medium distance rather than close to the lens. The trade-off is that focus is trickier, especially for moving subjects.

Video recorded on Sony a7S using internal XAVC-S codec at 24p and 120p. (Also includes some footage from the Nikon D750.)

In comparison to the a7S, the 2.3x crop of the GH4 makes for a flatter feeling image at the same equivalent field of view, for example 10mm instead of 24mm for a wide angle shot. Additionally, for those looking for an extremely shallow depth of field, it's easier to achieve on the a7S at 24-50mm compared to the equivalent field of views on a crop sensor. You don't have to resort to longer focal lengths and super fast apertures as often. When the subject is close to the lens, differences between crop and full-frame sensors become less noticeable. In particular, for extreme close-ups with a lens such as the Canon 100mm F2.8L Macro, focus is so shallow on full-frame to be almost unmanageable. A crop sensor is still an advantage for macro and telephoto work.

The Sony a7S has an excellent quality APS-C crop mode, with no loss of detail in 1080p compared to full-frame mode (unlike the Nikon D750). However there is a loss of quality in full-frame 50/60p mode, so shoot 24/25/30p for the best quality. If you need the best 1080p image at 60p from a full-frame sensor, the Nikon D750 will give you this. Also bear in mind, the 4K image over HDMI is significantly sub-par in APS-C crop mode with heavy artifacts, moire and false detail compared to the ‘real' 4K mode on the a7S which is full-frame and native 3840 x 2160 without any upscaling.

Creatively, I found the 120fps mode of the a7S very interesting but it produces soft results with quite a lot of moire. The NX1 and GH4 have a better image in 120fps and 96fps respectively but again both cannot escape moire and aliasing in this mode, so shoot at the cinema frame rate of 24p for best quality.

Rolling shutter is severe in full-frame 24/25/30p on the a7S. In APS-C crop mode it's much less of a problem. The skew is due to the time it takes to output every pixel from the 12MP sensor to produce each frame of video - around 25ms. This has the advantage of giving us much better image quality, but the disadvantage of slanted verticals with fast moving subjects.

Grading flexibility

The appearance of S-Log2 on the a7S represents the first time that Sony's professional picture profile has been implemented on a consumer camera. Prior to this S-Log was a $4000 upgrade to Sony's professional CineAlta cinema camera, the F3. S-Log2 can be finely tuned in-camera and it will give you a more cinematic image with an increased dynamic range over the standard color profiles. Unfortunately it's not a free lunch. S-Log2 has a minimum available ISO of 3200 and cannot go below, therefore you will need to use very fast shutter speeds or very strong ND filters in bright light, especially if shooting at fast apertures for the typical 'full-frame' shooting style. Ideally video needs to be shot at 1/50 for the most film-like motion cadence.

S-Log2 requires time and software expertise in post production to get it looking right. It's also tricky to shoot with as there's no built-in view assist, making exposure more difficult from the extremely low contrast display, and gauging color virtually impossible. Showing actors or clients low contrast S-Log2 material in-camera doesn't make for a very satisfying viewing experience.

Slow motion video shot at 120 fps on the Sony a7S between ISO 3,200 and 12,800 (S-Log)

Grading S-Log2 footage is also a challenge - beginners should approach with caution. I personally find myself spending a lot more time with software and a lot less time shooting as a result! The red channel in particular (with S-Log and S-GAMMUT enabled) needs an expert adjustment to balance it, otherwise reds have a purple bias. The flat picture profile on the Nikon D750 and the Canon LOG profile on Cinema EOS cameras is much lighter log and the desired look is far simpler achieve in post with these cameras.

External HDMI recording with the Atomos Shogun

Like the GH4, the Sony a7S can output a 4K feed over HDMI to an external recorder and/or display. Unlike the GH4, the HDMI output is of utmost importance since the camera does not have an internal 4K codec at all. So, for those wanting 4K you are compelled to buy an external recorder (currently in the region of $2000).

File sizes and compression quality for 4K recording on the a7S are therefore at the mercy of whatever codec is offered by your recorder, usually ProRes. File sizes end up far larger than the internal 1080p XAVC-S codec. I recommend ProRes LT as a good balance between quality and file sizes in 4K, but with a data rate of over 400Mbit, compared to 50Mbit for XAVC-S, it eats up 8x the hard drive space for 4x the resolution.

Video shot on Sony a7S using 4K HDMI out to Atomos Shogun recorder.

For in-depth information about 4K recording on the Sony a7S and the Atomos Shogun, you can see my shooting experience and reviews at EOSHD here:

http://www.eoshd.com/2014/12/winters-mirror-sony-a7S-atomos-shogun/
http://www.eoshd.com/2014/12/atomos-shogun-review-part-1/

High end features for pros

The low light performance of the a7S makes it unique, even around professional cinema cameras like the Sony F55 and Red Dragon. The small size of the camera is also an appealing aspect for filmmaking pros used to much larger rigs. If equipped with an equally small lens the a7S also becomes practical for professional drone use.

S-Log2 is a fantastic feature on the a7S for professional colorists. They will be able to match shots from the a7S to material shot with other professional Sony cameras like the F55. It makes a great small B-camera on a F55 or F5 shoot and also makes a good companion to the mid-range Sony FS7. S-Log2 is more challenging if you're a beginner. Experts will get on well with it.

The a7S does not do quite as nice a job of packaging the myriad features together into a cohesive whole as does the GH4. I prefer the ergonomics of the GH4 for video, and some basic usability aspects are poor on the a7S, such as the placement of the video record button. In terms of build quality the a7S feels like a consumer toy compared to a cinema camera like the Red Dragon or a professional grade DSLR such as the Canon 1D C, which shoots 4K internally, has a native EF mount, and full compatibility with weather sealed L lenses. Although the a7S body itself is sealed against the elements, your 4K recorder and Canon lens adapter probably won't be.

For photo-video journalists who wish to capture both stills and video on assignment whilst traveling light, the inability to shoot stills in video mode on the a7S is another ergonomic quirk that should never have been in the final camera. Battery life can also be a weak point, due to the excessively small body. The Sony battery grip helps by holding two cells at once. The cells are so small you wonder why it couldn't house 4 of them! The GH4 will run 5x longer on a single battery compared to the a7S, a remarkable achievement by Panasonic.

These complaints do not obscure the fact that there's a number of huge features professional filmmakers will lust for on the a7S, but the price is rock bottom for pros, and reasonably accessible even for most consumers.