@sammy. Sorry for the long post - it didn't start out this way - but thoughts kept popping in my head. Just another angle on this from a poor wannabe who has dreamt of an affordable high end image for years. Let me begin by saying that both cameras are phenomenal so I am looking at the finest points of pros and cons from my personal view.

To these eyes the GH4 1080p is not as good as it's 4k downsample. There is a big difference clearly demonstrated in resolution charts recently shot. My computer would need a significant upgrade to work with 4k so good HD will do me just fine. ( one could work with Cineform on a weak computer though )

High frame rates. The a7s has 120 fps albeit at 720p. The Gh4's 96 fps is no where near perfect and is lowish constant bitrate if I am not mistaken. I think it is lower res than the advertised Full HD so they may be comparable in actual quality.

Off camera recording. The inconvenience of the a7s having off camera 4k recording is mitigated by the fact that it may well be a perfect HD image that it spits out. Many GH4 users are considering it simply to end up with a perfect HD image. Uncompressed HDMI will always be superior to any laudible attempts for in/on-camera recording on 'lower end cameras' save for the very best cameras that offer Prores, RAW, Cinema DNG or the hi end Sonys and Canons offering very high bit rates. The hack was born out of a need for us to get beyond artefacts like mud, macro blocking and poor colour grading ability. But how much bit rate is needed to make us stop complaining but also manage data? The sweetpsot has almost been reached by the GH4 but in my grading efforts with the early samples of the mp4 files. . . . . Ummmm. . . .I realised that issues still exist with the GH4 codecs if one wants to do some serious grading with creative extreme shifts including the use of 3D luts. Any flavour of 4:2:2 would have sealed the deal for me with the GH4. I hope we all agree that no matter how sincere the effort with the codec an option for AVC Ultra, Prores or Cineform would make the GH4 have perfect 'sweetspot' on-camera recording that would make off camera recording obsolete. The fact that many are already budgeting for a recorder hints that there is a recognition that at many times higher quality may be desired that the cam doesn't deliver for discerning videographers. I suspect I am one if those sad perfectionists that wants to get beyond compromises in any way. So although the codec is good it ain't perfect. So the on board recording requirement for the a7s is less an obstacle if both may need an off camera recorder to really shine - and the GH4 would be best served with a 4k recorder ( because its HD is kinda meh to me - it's the aliasing that gets me ) wheras the a7s may look great even in HD. So to me I reckon I would have avoided the on board GH4 camera recording anyway - most of the time. For casual family stuff it makes sense. Having said all that - there will be incredible productions done with this GH4 as is. In fact it looks as good as the original RED one in many respects.

Having messed around with Red, Arri and Blackmagic files for years, one realises that as close to an uncompressed image grades much better every time for folk who have the time to tweak. I bought a BMPCC and converted to Cineform RAW grading is an absolute pleasure. I know what the fuss is about with Cinema DNG. For fast turn arounds - perhaps raw or uncompressed is overkill but for the ability to get creative that unfetterred HDMI port on a high end Sony cam is a Godsend and I mean it is truly a breakthrough. Never mind the 8 bit part - Sony are stingy with low end stuff giving this kind of accesss. Uncompressed hdmi is really cool because the offboard encoders can do so many more bitrates at will. Apart from raw you can record to whatever flavour you care for.

Personally I am pleased that finally we have a camera that allows us to tap into an uncompromised uncompressed 'probably' perfect HD image. Sony have put the effort into creating an impressive front end and basically allowed us to chose our back end and bit rate starting from uncompressed down to consumer bit rates. And Sony's image to my eyes is much more refined than the Panasonic's. On camera high bit rate would have been perfect - perhaps we will need to wait for the next iteration. But for now, we are spoilt for choice with recorders - blackmagic's stuff, Atomos' ninja star and plenty more. Roughly a few hundred bucks now. Too many HD HDMI recorders to name and many here may already have them.

I would imagine that using the APC crop with an anamorphic lens to a high quality recorder will look incredible.

So in the end it comes down to budget really and the final look. I am 'personally' convinced that the a7s will look more pleasing than the GH4 in most areas if both were to record their best image. ( still concerned about the jello as the one question mark on the Sony ). I suspect that on an HD home theatre the a7s will look as good as cameras that hitherto would have cost as much as a luxury car. It certainly appears on paper to have the wow factor. Time will tell. . . . Peace

@bozfx We are agreed that the 8 bit isn't as good as it gets - but if they included it may have begun to encroach on some serious high end visuals that they sell - interesting read none the less

http://www.redsharknews.com/technology/item/156-8-bit-or-10-bit-the-truth-may-surprise-you

Because this camera has so little noise, I suspect that it would have been the one camera that would have looked incredible with a 10 bit output - perhaps better than most of their current mid range offerings. The engineers must have seen that......Just wish Sony would offer that option at some point or would be cool to somehow hack Cinema DNG out of this camera - he he he he

http://www.sonyalpharumors.com/sr5-no-joke-sony-decides-to-split-announcement-a77m2-on-may-1-and-rx100m3-a-couple-of-weeks-later-likely-may-15/

A7s price announcement rumored to be delayed until May 15

Aw man, that blows. Was looking forward to learning the price so I could know whether I'm wasting my time or not.

I think we will see at least a few more models of cams that shoot 4K. And I also think that we will see some lower priced options in the HDMI recording market, even though these are not mass market items.

Good news is there are lots of choices. With either the Sony, 4K Studio or GH4 you get a big bump in resolution and lots of super lenses.

I'm leaning towards the BM 4k series with all the extra options, even though the sensor is smaller http://camcorders.reviewed.com/news/blackmagic-shows-off-new-4k-studio-camera-starting-at-3k

I would at least like to try the GH4 and the Sony before buying any of these, bringing along a Metabones adapter at least for the BM 4K Studio and the GH4.

Latest price rumor is $1800, which would make it competitive.

http://www.mirrorlessrumors.com/sony-a7s-priced-at-1800

2nd half of that video is without using S-Log2 and it shows how important it is to have. The highlights look awful compared to the fire in the shot on the beach by Den Lennie where the fire never seems to blow out regardless of ISO.

Some ISO test and other samples

http://www.dcfever.com/sony/readnews.php?id=10557

^ The Scotland smoked fish videos were recorded internally to 1080p with minimal postprocessing.

The Japan video was shot in UHD to a Blackmagic Design UltraStudio Pro recorder via HDMI.

These details are all in Den Lennie's blog posting: http://www.fstopacademy.com/blog/sony-alpha-7s-first-hands-on-shooting-review/

I'm thinking the U.S. price will be closer to $2500 than $2800, since the Luxembourg center's current a7R price is discounted.