Sony A7, A7R, and A7S...questions....

So my basic question is what is the relationship between the lower sensor megapixels and the higher video recording pixels.
A simple comparison on B&H's site although preliminary for the A7S will show you that the
A7 is effectively 24.3 MP, 6000*4000 resolution, with a 35.8 x 23.9 mm sensor, with 14-bit depth
A7R is effectively 36.4 MP, 7360*4912 resolution, with a 35.8 x 23.9 mm sensor, with 14-bit depth
A7S is effectively 12.2 MP, 4240*2832 resolution, with a 35.8 x 23.9 mm sensor, with 14-bit depth

So, why doesn't the A7 or the A7R shoot 4K when they seem to have larger maximum resolution?
Why is the resolution the A7S lower than the A7 and A7R when it can shoot better video at 4K?
Is this all "firmware"based? Are all three cameras actually the same with different limitations?

Could a raw feed out of the A7 and A7R that have higher resolutions give you better than 4K images?

I'm looking at this camera too as a possible 5Dmk3 replacement (with a metabones adapter to use my existing Canon lenses).

I am no expert, but I'm guessing that the lower resolution actually is beneficial to shooting video. When using Canon DSLR's the resolution used in video is far less than what you get shooting stills: and this leads to all the pixel binning (which leads to all the aliasing problems). Must be something to do with that when shooting 4K (the higher resolution is overkill for video)?

Heres the blurb from Sony:

Full Pixel Read-Out with Clean HDMI Out for 4K Recording
Line-Skipping has been the Achilles Heel of video recording DSLR and Mirrorless cameras since video recording was first introduced. Most full-frame and APS-C still cameras have extremely high pixel counts, which is great for still photography, but makes utilizing the whole sensor technically infeasible when recording video since scaling down, say a 36 megapixel image in real time would require a much more expensive image processor and generate more heat than such a compact body could handle. So traditionally these cameras skip lines when recording video, leading to major aliasing and moiré from the large sample gaps as well as decreased resolution and increased noise. However, the lower resolution sensor of the a7S is designed for video recording and features a full sensor readout without any line skipping. This means you will see a sharp image devoid of major aliasing and moiré whether recording internally at 1080p or externally in UHD 4K.

For times when the high quality 50 Mbps XAVC S Codec is not enough the a7S is able to output uncompressed UHD 4K (3840 x 2160) at a 4:2:2 color depth over HDMI to compatible third party recorders. Or, if recording internally to a memory card the HDMI can output 1080p at 4:2:2 for external recorders or HD monitors that don't support 4K inputs. The full lust of supported HDMI output signals is:

3840 x 2160 (30p/24p/25p)
1920 x 1080 (60p/24p/50p)
1920 x 1080 (60i/50i), YCbCr 4:2:2 8-bit/RGB 8-bit

THANKS Simon! It'd would be cool if you could take a 36.3 MP picture while maintaing the A7S 4K video though. But I guess the intrinsic setup doesn't allow for the best of both worlds, although the sensors are the same.

Then again, the 12.2MP images are just fine for me. I won't be doing any highway billboards any time soon.

Just to be 100% clear... The A7S has a completely different sensor than the A7 and A7r - which is why we have the lower megapixel count, better low light and why it can do 4k without skipping lines or binning pixels or any of the other crazy hacks these cameras do to still sensors to turn them into video sensors.

Looks like a cool camera. I for one would hold out for a few 3rd party reviews before leaping in.

I wish I had the money for one of these!

Simonpwood it is good to see you back and posting

Dave

Really? The sensor is completely different? The specs say otherwise. Is the sensor physically different OR is the sensor physically the same but read differently from a firmware point of view. The specs on BH indicate no difference.

Is there another source that tells you this?

The specs you posted tell you it's physically different, it has less pixels over the same area.

What Seamus VFX said... It's in the specs. The specs say a7s creates UHD by scanning the pixels - pixel by pixel. The full frame on the a7s is 4 by 3 shaped and has 4240 x 2832 pixels. The sensor of the a7r by comparison listed as 7360 x 4912. The a7 is listed as 6000 x 4000, the same sensor - reason for the lower megapixel count being it has an optical low pass filter to reduce aliasing.

I assumed that 35.8 x 23.9 mm meant they were physically the same size.....????

.....and the resolution was indicated on a secondary level...???


(((ahhhhhhh less pixels over the same area....OKOKOKOKOK)))

Yeah, the pixels are actually physical photo sites on the sensor. Bigger photo sites mean greater sensitivity to light but less resolution. It's all a balancing act; that's why there's 3 different a7 models.

Waternyc - none of this stuff is common sense. Sony Marketing does itself a disservice by not be clear on what these cameras can and can't do. Personally It's the lack of internal 4k recording that makes me nervous. I can't shake the feeling that in 6 months to a year there will be a Mark II or an "A7V" that has this feature.

tedmcneil wrote: Waternyc - none of this stuff is common sense. Sony Marketing does itself a disservice by not be clear on what these cameras can and can't do. Personally It's the lack of internal 4k recording that makes me nervous. I can't shake the feeling that in 6 months to a year there will be a Mark II or an "A7V" that has this feature.

That's a given; the technology is moving on and everything will improve. 3D was a flop, so now the big push is going to be UHD or 4K. Sony will really start pushing 4K cameras soon, not because they want to sell 4K cameras, but because they want to sell 4K TV's.

But who is really ready to deliver 4K anyway? Most of the work filmed in 4K on the RED cameras over the last few years has been delivered in HD or 2K. Most CGI houses are loath to have to do CGI in 4K.

The Arri Alexa continues to be one of the most popular cinema cameras; it's not 4K. The C300 continues to be one of the most popular cameras for TV drama and documentary; it's not 4K.

I reckon the A7s is going to be popular more as an HD camera rather than a 4K camera. Like a C300 you get to use a 4K sensor which downsamples to HD; making a very high quality HD image. People are going to be using this thing as a budget C300; I for one am looking forward to see how it handles in this capacity.

simonpwood wrote: I reckon the A7s is going to be popular more as an HD camera rather than a 4K camera. Like a C300 you get to use a 4K sensor which downsamples to HD; making a very high quality HD image. People are going to be using this thing as a budget C300; I for one am looking forward to see how it handles in this capacity.

I completely agree. 4k for delivery is long way off and this camera is going to be a monster hit. Based on what I see at press conferences, this sucker should be huge with newspaper/web journalists. And even if there was no 4k - the S-Log2 Gamma and high ISO features would be good enough reasons to purchase it.

I'm hoping that the "give and take" with the sensor specs are based on technical essence, have the expected results, and the rolling shutter fixed.....

...here should be the first example where MP aren't all that matter....