Review: Sony PXW-X70 Professional XDCAM Compact Camcorder

In my previous article on HD Camcorders for Webcasting, I outlined why I thought there was need for a medium-sensor video camera to split the difference between the pros and cons of small-sensor camcorders and large-sensor interchangeable-lens video cameras and DLRS.

Most users and reviewers focus their efforts in video camera comparisons on a similar group of features that are deemed important for professional video production acquisition, but this group of features often overlooks the sensor size beyond its effect on focal length and crop factor.

Why Sensor Size Matters

Sensor size is one of the most important features to consider when comparing video cameras, especially seeing that in only a matter of a few years, acquisition and delivery resolution jumped from NTSC 480i to HD 1080P and now 4K or UHD 2160P. Ignoring adjustments to compensate for non-square NTSC pixels recorded in interlaced fields, acquisition and delivery resolutions have effectively jumped by 25x in a single frame, while the base sensor size in similar classes of camcorders has remained the same.

Manufacturers compensated for the lack of change in sensor size through a variety of methods, some more successful than others. The first big move was to abandon CCD sensors in favor of CMOS sensors and while the 1/3" sensor size increased to 1/2.84" or 1/2.88", the rest of the improvements were designed to improve the signal to noise ratio, native resolution, exposure latitude, and a variety of other important signal processing improvements. Ultimately, there is a limit to the image quality that a small sensor can deliver, and the low-hanging fruit on the tree of image-quality gains is to increase the sensor size.

Sony X70 vs. Canon XA20/25

The Sony X70, with its 1" Exmor R CMOS sensor (20MP native, 14.2 MP effective pixels), is the first in what I expect to be the new norm for professional camcorders—medium-sized single-sensor camcorders, as opposed to three 1/3" sensor camcorders. The trade-off when moving to a larger 1" sensor is that companies need to design new lenses to cover the larger sensor, so initial offerings are not going to be as fast nor have the same focal length range. In the case of the X70, Sony paired it with a 12x Zeiss F/2.8-4.5 lens.

Consider that the X70’s most direct competitor is the Canon XA20/25 that pairs a 1/2.84" sensor with a 20x f/1.8-2.8 lens. If you compare the XA20/25 lens focal length range and maximum aperture, in isolation of consideration for the sensor size, you might conclude that the Canon system has superior low-light sensitivity, can zoom in further, and be able to attain a shallower depth of field, but you would be wrong. Sony claims that the X70’s 1" sensor is 1.87 stops brighter than it previous generation HXR-NX70’s 1/2.88" sensor.

On the other hand, the Canon f/1.8-2.8 is 1 1/3 stops faster than the Sony Zeiss f/2.8-4.5 lens. When the dust settles on this low-light sensitivity duel, and acknowledging that I am using a comparison of two Sony sensors to determine how light-sensitive the Canon XA20/25 sensor is, the Sony X70 may have a slight 0.5 f-stop lead. The depth of field comparison between a larger sensor and slower lens and a smaller sensor and a faster lens isn’t that interesting, either, and the news gets even duller before it gets better.

When I factor in the generation difference between the slightly older Sony NX70 vs the Canon XA20, I’m comfortable calling the discussion of the theoretical native low-light sensitivity difference between the Sony X70 and Canon XA20/25 a moot point, and too close to call, without using a waveform monitor. This is consistent with the limited real-world comparisons I performed when I owned both cameras at the same time, for a whole day, before I shipped my Canon to its new owner. When sensitivity is this close, who really cares in real-world usage – but despite this, I’m not going to call the usable low-light sensitivity comparison a tie. As promised, the low-light comparison gets more interesting when you add additional factors to the comparison.

The usable low-light sensitivity in real-world usage is a combination of three factors: lens maximum aperture, sensor size/sensitivity, and signal-to-noise ratio beyond 0dB of gain. We have determined that the first two comparisons result in a tie, but the beauty of the Sony X70, and its larger 1" medium-size sensor, is that it can produce a cleaner and more usable image when you increase the gain (Figure 1, below).

Figure 1. Comparing the Sony X70 and the Canon XA25 at high gain. The Canon image is on the left, Sony on the right. Click the image to see it at full size.

In all cameras, the higher the gain, the noisier the image. In general, a larger sensor is better able to handle higher gain values. This holds true when comparing the Sony X70 to the Canon XA20/25. The Sony X70 delivers a cleaner, less noisy image well beyond the range where the Canon XA20/25 image starts to fall apart.

By starting with a higher-resolution sensor, the Sony X70 has a few tricks up its sleeves to differentiate it from the 1/3" HD camcorder class it is outclassing. First is the ability to perform a 2x Clear Image Zoom. This brings the effective zoom range to an impressive 24x, a full-frame equivalent range of 29-696mm. Sony does this by zooming on the sensor, which has plenty of leftover resolution, and not on individual pixels, an undesirable technique otherwise known as digital zoom. The X70 also has a v2.0 firmware upgrade with an optional 4K upgrade license planned for June 2015 that will support 3840x2160 internal recording. The MXF wrapped XAVC-L 60Mbps 4:2:0 8-bit codec will be available in 29.97p, 23.98p, and 25p frame rates. By comparison, the current internal HD recording is available in XAVC-L 50Mbps 4:2:2 10-bit at up to 29.97p or 60i frame rates, or AVCHD 28Mbps 4:2:0 8-bit up to 59.94 frame rates.