Full frame Sony A7S ‘with 1.1x sensor crop in 4K mode and XAVC-S codec’

A7S would be beautiful with the Canon 50mm F1.2L

I’ve just had some information from a source that may be of interest to those awaiting Sony’s NAB announcement.

As we know from previous rumours the Sony A7S will feature a 12MP sensor. This is very good news for video.

My source says this will be 4230 x 2820 for stills. The cinema DCI format of 4K as seen in the GH4 is 4096 x 2160 which would mean only a very small crop of the sensor.

However according to the source the A7S features the same codec as the AX100, XAVC-S, which is Sony’s de facto consumer 4K standard. This consumer codec only supports 4K at Ultra HD resolutions in 16:9, which means a slightly larger crop of 3840 x 2160 (around 8MP).

That amounts to a 1.1x crop over full frame in terms of how wide your lenses are… The same crop as Speed Booster on APS-C (E-mount). Still very little difference so we really are going to get real full frame VistaVision 4K out of this beast.

I also did some research on the AX100’s implementation of XAVC-S. It records in MP4 format but perhaps rather disturbingly it has a much lower bitrate than the GH4’s 4K codec. It is just 60Mbit/s vs 100Mbit/s on the GH4 in Ultra HD. I have not yet graded any footage from the Sony AX100 but it will be interesting to see how XAVC-S stands up at that bitrate. It is a very modern codec and bitrate isn’t everything.

Sony A7 and Canon 50mm F1.2L

Above: my Sony A7R and Canon 50mm F1.2L – a great match

The last piece of info I was told relates to HDMI. It is uncompressed 4K out of the port but it isn’t clear whether this will be 10bit like the GH4.

Also it is not clear yet what the colour sampling is for the HDMI – 4:2:0 or 4:2:2. Part of the reason the GH4’s image looks so great is that the whole imaging pipeline is 10bit 4:2:2 and the codec only introduces 4:2:0 sampling at the very last encoding stage.

Will I buy one?

So far I have a lot of excitement for the 12MP full frame sensor on this beast, but some trepidation for how Sony might handle the other aspects of the camera such as the codec and rolling shutter… so let’s see.

Low light performance should be amazing with the full frame sensor and the 1.1x crop will be a great match for my full frame glass.

However the GH4 also has very respectable low light and only a 1.5x crop over full frame if used with the 0.71x Speed Booster from Metabones.

So the potentially better codec on the GH4 along with Super 35mm standard sensor size with Speed Booster, and of course a sensor not too big for my PL mount Cooke lenses might be enough to swing it in Panasonic’s favour, at least for me. Let’s see what happens as NAB gets under way. I do love the full frame look.

I’ll have more news as soon as it comes…

And in case you are wondering where Canon are in all of this… so am I!