HD Webcasting with the Sony NEX-FS100

Advantages of Autofocus

Before the FS100, I honestly never used the autofocus on my previous camcorders. I would sometimes use the push autofocus button if I needed focus help, but I always kept my cameras set to manual everything and my camera operators were trained to focus manually. Granted, a small-sensor video camera has a great depth of field and lacks detail, so it's much more forgiving than focusing on a large-sensor video camera. This is why modern photographers typically use autofocus because their photographs are being blown-up larger and zoomed-in more than ever before, and accurate focus can make or break a shot more, especially when you are filming with a shallow depth of field. Since the FS100, I longed for some autofocus functionality. If I used the FS100's native E-mount lenses I could get CDAF, but the current lineup of E-mount zoom lenses are slow with the following zoom lens offerings: 18-55mm f/3.5-5.6, 18-200mm F/3.5-6.3, and 55-210 F/4.5-6.3. The 18-200mm "kit lens" that I opted not to purchase is the only lens that many FS100 users own might start at f/3.5 when fully wide on the 18mm end but by the time it reaches 50mm it is limited to f/5.6. This might be fine for outdoor shooting, which incidentally is challenging on the FS100 because it lacks an ND filter wheel, but I film most of my webcasts at f/3.5-4.0 in order to minimize the use of noise-causing gain. Outside of stage performances where I want a great depth of field, f/5.6 doesn't defocus enough for me on a webcast where I want to minimize the background detail so that my web codec can spend its precious bitrate resources on the important parts.

I still don't use the PDAF that often, but there are times where it does help me get shots I otherwise wouldn't be able to manually or when reaction times are important. One examplefrom filming conferences that are being webcast is when there is a speaker on a large stage who walks to and fro and fore and aft. I like to film these at f/4.0, usually on the long end of my Minolta AF 70-210mm f/4.0 "beercan" lens, for the benefit of a defocused background, but when I have a walker I either have to stop-down to f/5.6 or lower to increase the area that is in focus at the expense of a desired level of background defocus or use PDAF. In this scenario PDAF works very well, as long as you keep your subject framed on one or more of the 15 point focus markers that become visible on the LCD when PDAF is enabled-the active point is highlighted in green.

Performance-wise, the PDAF is accurate and fast, regardless if you are using a screw-driven focus system on the old Minolta AF lenses, which is supported with the LA-EA2 adapter or a newer Sony SAM (silent autofocus motor) or SSM (SuperSonic Motor) drive. Don't get caught-up in marketing hype that SSM is faster and quieter than the SAM focus system and thus better for video. Unless you're using on-board audio with a shotgun microphone, the camera audio doesn't matter much. The iris changes are actually louder than the autofocus noise anyway, and the autofocus speed on video with PDAF is a magnitude faster than anything in CDAF. I can't discern a speed difference in either of the systems that would matter in all but super-slow motion. In fact, I think the PDAF speed is too fast and might even look a bit unnatural as it is faster than a human would ever focus-pull. I wish Sony would allow an AF speed adjustment so the autofocus would look more "film-like."

Outside of the webcast market I need PDAF on my FS100 for when I mount my camera on my Kessler KC-Lite Crane (Figure 4, below). Manual focus used to be OK on a camcorder, but if I want to use a shallower depth of field, then one manually set focus setting just won't work, especially if my subject is moving.

Figure 4. 3-camera Sony FS100 shoot filmed by Greg Lam, Shawn Lam, and Scott White.

In the below Heart tribute band video that I produced, and shot with three Sony FS100s, I was operating the crane angle and I filmed two takes for each of the three songs. At first I was going to manually focus the first take and then use PDAF for the second, but it quickly became obvious that PDAF was the way to go for the crane angle if I wanted as much usable footage as possible. In the end, I had to discard most of the manually focussed crane footage because it was out of focus. The other two camera angles were manually focussed both times.