Sony Breaks New Focal Length Ground in Professional Video--and No One Notices

Sensor Size

I have always felt that the 1/3" sensor size was fine for SD work but not quite up to the task for HD work, especially when gain (higher ISO) was required. My 2010 side-by-side comparisons of the Super35 FS100 and 1/3" NX5 camcorder convinced me that if I wanted a cleaner video signal (less noise), sharper image, and one that had my subject pop more than the flat image that small sensors--with their great depth of field--are limited to, I had to move all my productions to large-sensor video cameras. I eventually did add back a camcorder in the 1/3" sensor class, the Canon XA25 (Figure 4, below), which I recently replaced with a the 1" sensor Sony X70, for when image quality wasn’t paramount and for when a camcorder was the best tool for the job.

Figure 4. The 1/3" sensor Canon XA25

Now that 4K UHD acquisition and delivery are growing in demand, I feel that a 1/3" sensor just won’t be up to the task of such a high-resolution image. Sure, sensor technology has come a long way since 2010, but the laws of physics as they concern light transmission haven’t, and a larger sensor will result in a cleaner and sharper image.

Teleconverters

One of the benefits of the e-mount, with its shallow flange back distance, is the ability to mount most other lenses on e-mount video cameras. This requires a simple adapter for most lenses or--in the case of Sony a-mount and Canon EF lenses--a powered adapter. With adapters comes compromise. I’m not going to get into that discussion in this article, but I’ll simply acknowledge that there are benefits to sticking with native lenses on Sony e-mount video cameras.

Up until today, there were only a few options for extending the natural optical reach of a particular lens using a teleconverter. Sony has a pair of legacy a-mount 1.4x and 2.0x teleconverters (Figure 5, below) that could be paired with their a-mount 70-200 f/2.8 lens, but who wants to invest in an a-mount lens, considering there is little demand for a-mount cameras or lenses in the resale market? Canon has a similar option. Ultimately, combining a heavy lens to a teleconverter to an adapter to a video camera feels very cobbled together, and because of the additional length, it requires a rail system to protect the lens mount from strain.

Figure 5. The Sony TC 2.0x teleconverter

The new Sony 1.4x and 2.0x teleconverters for the Sony 70-200mm f/2.8 FE GM lens (Figure 5, above) eliminate the need for a smart adapter, and as a result, likely also the need for lens-support rail system. Teleconverters come at a light transmission cost--2 stops for the 2.0x and 1 stop for the 1.4x, which means the above f/2.8 lens acts like a f/5.6 or f/4 lens in terms of light transmission.

Large-sensor video cameras handle higher gain or ISO levels better than do smaller-sensor video cameras. This comes down to physics, as I alluded to earlier, and because of this, filming with 18dB of gain on a Sony Super35 camcorder can result in a cleaner video signal than filming at 0dB on a 1/3″ camcorder, which is about the difference when you compare both scenarios with the X160/180 at full telephoto. While f/5.6 might sound like a lousy starting point when you need light transmission, consider that 2 f-stops of light transmission is equivalent to 12dB of gain, and the difference between the X180’s f/1.6 constant aperture lens and f/5.6 is 3 2/3stops, or about 22 dB of gain. Measuring actual light transmission using f-stops is all theoretical, of course, as opposed to T-stops that measure the actual light transmission, and the light transmission of the X180’s lens is reported to lose about a full stop of light transmission through its 25x zoom range, bringing the actual number below 3 stops, or 18dB of gain.

If you’re keeping tabs, with the addition of the 2.0x teleconverter on the SEL 70-200 f2/8 GM lens, we can attain a 600mm focal length. This is almost as far as the reach of the 25x X160/180 camcorders with their 25x zoom.

Zoom Revisited

Optical Zoom > Digital Zoom. There is no debating this when traditional digital zoom merely zooms in on the resolved image and is the equivalent to zooming in on pixels beyond a 1:1 ratio. Consumers don’t always understand this, so many consumer camcorders are comically marketed featuring extremely high digital zoom numbers.

Super35 sensors have more resolution than is required to resolve an HD (and even 4K image). This additional resolution is useful for keeping noise levels low with high ISO/gain settings, but it’s also useful for a new type of digital zoom that Sony calls Clear Image Zoom. Sony first introduced this feature to the professional market in late 2012 with the APSC sensor EA-50, but because that video camera used a sensor that was designed for photo use and was smaller than a Super35 sensor, the image quality wasn’t on-par with the older FS100 or the 2012 FS700. Clear Image Zoom is available on Sony’s a7s series of professional interchangeable lens cameras, that are more video-centric than the A7 and A7r models, but up until now this feature never made it to the FS line of professional video cameras.

The Sony FS5 has many desirable features to its credit, including 4K UHD internal recording, 10-bit HD output, SLOG3, and finally a form factor that allows the video camera to be operated like you would a handheld camcorder. The LCD placement of the FS100/700 has long been my biggest complaint with that line of video cameras as it made handheld work without a rig all but impossible. Users and the media were quick to talk about all these features but didn’t give much coverage to the 2x Clear Image Zoom feature that can be controlled via the zoom rocker on the ergonomic SmartGrip.

Using Clear Image Zoom results in an image that is very similar to using only optical zoom, but without the dramatic loss in light transmission. I hesitate to call it a form of digital zoom because it results in a full-resolution image and in many senses in superior to using a teleconverter for the light transmission loss alone.

Stacking all these zoom range-extender technologies one on top of each other results in a maximum FFE focal length of 1200mm. This is equivalent to 46x zoom, relative to the 25x on the Sony X160/180. Now, it’s likely you don’t need all that zoom range and a 20x range (576mm on the NX3) might be all the reach you need, but now you finally have a few tools to accomplish this zoom range on a large sensor video camera. My advice would be to pass on the 2.0x teleconverter unless you really do need to get into the >600mm FFE range or are using the FS100 or FS700 models that don’t have and will likely never benefit from firmware upgrades to add Clear Image Zoom.

By comparison, the 1.4x teleconverter only adds 40% more zoom range but the cost is a more reasonable 1 stop of light transmission loss. What’s more, a 200mm lens can reach 420mm FFE with the 1.4x TC alone.

If you have the FS5 or FS7 (via a future firmware update), the Clear Image Zoom will get you to 600mm on its own with a 200mm lens. Pairing the 1.4x TC with these cameras means you don’t have to push the Clear Image Zoom right to the end of its range, as the end of the range is where performance would suffer the most. The 70-200 lens and TCs were just announced, so I haven’t been able to test either on my FS5, but the lens is scheduled to ship in May 2016. No date was provided for the TCs, and price is to be determined.