No one was surprised to see the introduction of several 4K camcorders at CES 2014. Sony’s announcement of the 4K (Ultra HD) FDR-AX100 for less than $2,000, however, was a surprise. UHD camcorders still had an aura of exotic technology with a high price tag, not a technology targeted to semi-professionals or even consumers.
Paired with the unexpected price is the camera’s surprising technical capability. While the world of consumer camcorders is dominated by 1/3-inch sensors, the AX100’s CMOS 1-inch (1-Type) BSI (backside illuminated) Exmor R sensor offers a true breakthrough. The Super 16-sized sensor enables, at wide apertures, a moderately shallow depth of field (DoF). Of course, to open the aperture when shooting in bright light, ND filtering is required. After shooting with DSLRs, I was happy for the AX100’s built-in ND filters (0, 1/4, 1/16 and 1/64).
The camera’s 1 inch (13.2mm x 8.8mm) CMOS sensor and BIONZ X processor enable full-resolution Ultra HD (3840 x 2160) shooting at 24p and 30p with XAVC S encoding. The inclusion of a 24p (23.976) frame rate in a camera that will likely be bought by those used to shooting 60i is also surprising. The alternate UHD frame rate, 30p (29.97), runs counter to the recent trend of some consumer camcorders to offer 60p.
The AX100 introduces Sony’s XAVC S codec to a market where AVCHD has been the norm. XAVC S uses MPEG-4 AVC/H.264 for video compression and linear PCM for audio compression, saving files in an MP4 wrapper. XAVC S (H.264 HP@5.1) has a VBR data rate of 60 Mb/s, and uses 2-channel, 16-bit, 48 kHz PCM audio. A Class 10+ SDXC memory card is required for recording in XAVC S. You also must use Class 10 SDXC UHS-1 cards to be able to format a memory card in the camera
Almost lost in the camera’s launch announcement was the AX100’s ability to shoot Full HD (FHD) at 24p, 30p and 60p at a VBR data rate of 50 Mb/s. The sensor employs pixel binning to increase sensitivity from 6 lux to 3 lux (at 1/60s). Binning cuts in half the number of photosites to be read out, which enables the 60p frame rate.
FDR-AX100 Recording Formats
XAVC S 4K
XAVC S HD
3840 x 2160
1920 x 1080
1920 x 1080
28 Mb/s (max.)
Up front the AX100 has a Carl Zeiss Vario-Sonnar T* 9.3-111.6mm (29-348mm) 12x zoom lens. The maximum f-stop increases from f/2.8 to f/4.5 as one zooms. The minimum f-stop is f/11. Unlike some DSLRs, the AX100 downscales sensor data to 3840 x 2160 pixels without skipping lines. (Line skipping is one cause of moiré.)
For those whose computers cannot handle XAVC S, the AX100 can record using AVCHD: 60p at 28 Mb/s, and 24p and 60i at 24 Mb/s. A 720p120 slow-motion AVCHD recording option is also available. Dolby 2.0 or 5.1 audio can be recorded when AVCHD encoding is employed.
The AX100 has a 921,000 dot, 3.5-inch foldout LCD and a tiny, 0.39-inch, 1,440,000 dot OLED viewfinder. If you wear glasses as I do, you’ll not be able to see the entire image.
Although the AX100 supports either an audio limiter (without AGC) or manual audio level control, the latter controls audio only from the internal mic.
Sony markets the AX100 as capable of being operated manually. While that’s literally true, the configuration of its manual controls makes doing so difficult. Let’s look at how manual mode works when setting shutter speed as an example. Press the Shutter Speed button and then dial in 48 or 60. Ideally you’d lock this setting; the AX100’s dial remains live, however, all but guaranteeing that at some point you’ll accidently change the shutter speed.
The solution: Initially use a menu to set Camera Data Disp to “on.” Then use menus to set the AGC Limit (I recommend “up to +18dB”) and the AE Shift. (I found “-0.7” prevents highlight clipping.)
After setting these options, preset iris, gain and shutter speed by pressing the Program AE button. An “A” will appear beside each value.
Press the Shutter Speed button. Dial in the shutter speed. Press the gain button twice to lock the shutter. An “A” appears next to the gain and iris values. The AX100 now will automatically adjust the aperture, and the gain, if necessary, to make spot-on exposures. The AGC Limit and AE Shift presets are honored.
To lock exposure, press the Manual button and an “E” will appear beside the iris and gain values. Alternately, to manually set exposure, press the Manual button and use the dial to set values. Aperture (and gain, if necessary) will be adjusted as you turn the tiny dial. (I’d prefer to use the lens ring to set exposure—it feels more natural to me—but the AX100’s lens ring can control only focus or zoom.) The AGC Limit will be honored but AE Shift will not. To return to auto, press the Manual button again.
The AX100 has several options to aid manual focus. It’s unfortunate that Sony placed the magnification button on the right side of the camera where it’s unlikely a standard-issue human can reach it. A menu item enables yellow, red or white peaking so you can accurately adjust focus using the lens ring. Turning peaking on/off requires many menu steps, however, so I ruled out using peaking. I decided to leave the AX100 in AF mode, where it tracks focus very well. To lock focus, press the AF/MF button. To return to AF, press the AF/MF button again.
Initially I shot with Cinematone but switched when I found it added a slight pink tint to neutral shades.
Another decision you need to make: 24p or 30p. The advantage of 24p is that Blu-ray does not support 30p. Potentially, 4K Blu-ray will not either, preventing optical storage of 2160p30.
One of Sony’s 4K-UHD marketing slogans is “Four times clearer than HD,” and video recorded by the FDR-AX100 plainly shows Sony engineers have worked their magic to deliver on the slogan. Video captured by the AX100 is very sharp, with high contrast and natural color.
Sharpness curves. Rightmost point is 3840 pixels.
In light of math predicting that UHD will not appear to have greater resolution than Full HD at typical viewing distances, my experience matches reports from others indicating that AX100 video is distinctively sharp even on lower resolution displays.
To help explain this paradox, the graph of sharpness curves (right) presents a set of frequency response curves from a Sony camcorder that demonstrate the effect of manually adjusting sharpness. (The AX100 does not provide controls to adjust sharpness, saturation, brightness or contrast.)
I’ve viewed AX100-shot video extensively and can generalize that most footage from the AX100 has an inordinate amount of aliasing. My experience matches lab testing conducted by the German site www.slashcam.de, which reports that the AX100 has “significant sharpening” and “too strong … sharpening produces distinct halos around dark edges.” Thus the sharpening boost is most likely similar to the orange (“8”) curve.
Looking at the graph, the energy (signal strength) under the orange curve is so great that monitors with display resolutions less than 4K will still display a sharp picture.
Sharpening—edge enhancement, i.e., edge hardness—creates two side effects: judder and aliasing. Because our eyes sense motion judder based on a moving object’s edge hardness, low-frame-rate video will exhibit judder. To help prevent judder (as well as CMOS rolling shutter artifacts), avoid panning unless following an in-motion foreground subject, and always pan with the subject. Never allow a shutter speed faster than 1/60th of a second because short exposures decrease motion blur, which reduces edge hardness, thereby keeping video from exhibiting unpleasant strobing.
With excessive sharpening on object edges, very fast transitions create high frequency information. When the frequency of this information is greater than half of the digital display’s resolution (its sampling frequency), aliasing appears. Aliasing can materialize as moiré or line-twitter (not the same as inter-line flicker). Twitter occurs when a camera moves across fine detail such as tree leaves. The faster the motion, the higher the twitter frequency. Recordings are less likely to exhibit aliasing when made by digital cinema cameras (which do not sharpen) or professional 4K camcorders such as Sony’s FDR-AX1 (which offers sharpness control).
Assuming your NLE employs a very good anti-aliasing filter prior to downscaling UHD to FHD, aliasing can be diminished by creating HD videos. Doing so, however, likely runs contrary to your reasons for buying a UHD camcorder.
Because televisions have several resolutions, computer monitors have many resolutions, and software windows can be sized to most any resolution, there is no onedisplay resolution. Reported artifacts will, therefore, range from none to many. Reports of video quality will vary widely, thereby creating QC difficulties for producers.
When presented on a large screen, 4K video allows viewers to visually roam within a picture. To take advantage of super-resolution images without introducing aliasing, mount the AX100 on a tripod or, when handheld, engage Active Stabilization. When fine detail is present in a scene, do not pan or zoom. To minimize rolling shutter when shooting handheld, keep focal length short (under 1/4x zoom).
Aliasing not caused by over-sharpening is generated within a sensor when the information frequency that arrives from a lens is greater than one-half the sensor’s resolution. Sony seems to have effectively controlled this source of recorded aliasing.
The process of editing UHD XAVC S, although time-consuming, was remarkably straightforward. Here is some of what I learned.
Avid Media Composer’s AMA capability can access XAVC files. Use its transcode function to generate 2160p DNxHD intermediate files. (This is not a fast process.) Media Composer cannot export a 2160p movie.
Apple FCP X offers the option of creating ProRes proxy files during XAVC import. You can begin editing the XAVC files while proxies are being created. Once proxies are ready, you’ll edit them. (Select “Playback: Use proxy media.”) Before export I found I had to select “Playback: Use original or optimized media.” FCP X can export 2160p resolution movies.
Adobe Premiere Pro CS6 lived up to its reputation of being able to edit anything. After setting its source and program monitors to 1/4 resolution—you may see unpleasant aliasing—I simply started editing the XAVC files. Premiere can export 2160p resolution movies.
To play video on my MacBook or upload 2160p files to YouTube, I export using the ProRes 422 LT codec. UHD exports take a long time. Aliasing was present when I viewed UHD exports on my 63-inch HDTV connected via HDMI to my MacBook.
Uploading 2160p obviously also takes a long time. When watching movies using Apple TV, artifacts are much reduced because Apple TV selects either a 1080p or 720p YouTube stream.
Sharing edited 2160p video via the Internet is not a universally practical solution—nor does such a solution yet exist. Streaming performance varies from very good to impossible. Contrary to claims that highly compressed H.264 must look terrible, in fact it looks quite good. It’s reasonable to expect that H.265 will make the 4K distribution and viewing experience much better.
To view 2160p streams, I use the Chrome browser because it’s the only one that enables me to select a 4K H.264 stream.
Watching 4K in 4K
It’s safe to say that no consumer camcorder footage has looked as good on a 4K screen as that from the FDR-AX100. Artifacts were so minimal that most viewers would never notice them.
I discovered that UHD televisions can play exported 2160p QuickTime .mov files compressed with the x264 codec and 48 kHz PCM audio. Codec settings were 60 Mb/s, High Profile, Level 5.1, 3refs and CABAC.
Pros: The 1-inch Exmor R CMOS sensor, with almost 21 megapixels, provides an AX100 shooter with multiple capabilities: Ultra HD (2160p) and Full HD (1080p) video, plus up to 20 megapixel photos. The wonderful built-in ND filter coupled with the large 1-inch sensor enables shallow DoF video and photos. Offering much higher Full HD data rates than does AVCHD, Sony’s new XAVC-S codec supports 24p, 30p and 60p at 50 Mb/s. UHD can be captured at 24p and 30p with a data rate of 60 Mb/s. To provide maximum fidelity, when using the XAVC-S codec, 2-channel audio is recorded without compression (LPCM). Unlike many DSLRs, the AX100 has a stereo microphone mini-jack and a headphone mini-jack.
Cons: My concerns include available recording options and the AX100’s manual control system. Moving objects exhibit motion judder because UHD cannot be captured at 60p. (Sony may consider this a justification for not offering a UHD data rate greater than 60 Mb/s.) Although the built-in microphone can capture 5.1-channel AC3 audio, surround sound cannot be recorded when using the XAVC-S codec. And although the AX100 has audio level controls, they cannot be used when an external microphone is connected. Equally strange, this UHD camcorder records up to 120fps slow-motion video, but only using 720p AVCHD—thereby necessitating an impractical 8x upscale to obtain slow-motion UHD. Although the 1,440,000-dot OLED EVF features amazing technology, its tiny size and optical limitations make it relatively unusable for those of us who wear glasses. While manual control is marketed as an AX100 feature, the poor user’s manual, a complicated menu that mixes photo and video options, the DV-era manual control system, plus the bizarre placement of the magnification button placement are all reminders that the AX100 is best used as a point-and-shoot camera that happens to offer UHD resolution. Last but certainly not least, there is no sharpness control to enable a shooter to attenuate aliasing (moiré and twitter/shimmer).
Bottom Line: The AX100 records UHD video with high contrast and with extreme sharpness. For those who want a more “filmic” image, the AX100 is not your camera. Its more expensive big brother, the AX1, captures an image that will be far more pleasing to many shooters. The AX1, unlike the AX100, also provides a sharpness control. As with most CMOS cameras, the best video will be achieved when the AX100 is mounted on a tripod and both zooming and panning are held to a minimum. Doing so also helps prevent rolling shutter artifacts and offers the best chance of preventing potential twitter/shimmer. Although the lens, sensor and to some degree the XAVC-S codec are all state of the art, most other camera functions feel like a “committee” mash-up done by Handycam marketing, still photo engineers, and consumer DV camcorder firmware engineers.