This last weekend I took the FS-700 out to my club's cyclo-cross race at Lake Hodges. Action sports are notoriously hard to get in focus while recording a live event. You never know which way the athletes are going to bob and weave. This seemed like the perfect opportunity to test the Sony FS-700's auto-focus feature at 240fps. To really commit to this project, I decided to go the follow-focus equivalent of "full commando" and leave my nice Arri MFF-2 at home. No guts, no glory!
Auto-focus works with Sony's E-mount lenses, such as the 18-200mm lens like I had, or the Alpha lenses with the LA/EA2 adapter. Without the adapter; i.e. with E-mount lenses it seems as though the camera is using contrast detection. With the LA/EA2 adapter the camera uses phase detection, which is far superior, but your lens must constantly be at f/3.5 for the feature to work! Most of my day I was at f/6.3-f/8 because the 18-200mm stock lens is very, very slow at long focal lengths. I've never met anyone, outside of GoPro users, that shoots sports without a long lens. 200mm even seemed short, but that's a subject for a different article. I'm sure Martin didn't want me too close to the action, especially when he sees MY edit of the race!
For standard auto-focus it's as simple to setup as flipping a switch on the control panel side of the camera near the lens mount. There's also face detection auto-focus available in the menus, but I couldn't really test that in my situation.
I found a couple common trends after reviewing the footage. First, the contrast auto-focus gets it right about 50% of the time. So 50% of my shots ended up being out of focus at some critical point. Second, if the auto-focus gets confused it tends to focus further out to the background rather than staying on a fast moving subject. Of course there is going to be less contrast on the athlete when there's motion blur, but the failure mode was still inconsistent. However, I can't complain too much. I didn't have an assistant to pull focus. I didn't even have much much loved Arri follow-focus (Sorry baby. Please forgive me. I want you back!). So my best bet was to get multiple takes of similar action of the athletes and choose the best one. Sometimes it took four takes to get the athletes where I wanted them and sufficiently in focus. It would have probably taken eight takes if I was operating and pulling focus with peaking turned on.
One item I could see as room for improvement is if the camera could somehow indicate that it tried to focus at the minimum focus distance of the lens, so I knew to back up a bit if that was the issue. I still don't know if that was my issue on some of the long lens shots.
The video below shows a series of similar shots side by side where the auto-focus succeeded and failed. As I mentioned previously, the hit and miss ratio was about 50/50. So between my inexperience capturing action sports and the auto-focus I ended up abandoning about 60% of the shots, and that's before the edit selection. Unfortunately we don't have the LA/EA2 adapter, nor alpha mount lenses at the shop, so I can't provide a comparison or opinion on the phase detection auto-focus versus the E-mount native contrast detection auto-focus. One other item I included in the sample video are two examples of the focus transition time. At 240fps it takes a few seconds for the camera to transition between focus points.
The main question is would I use it again? That's a definite yes, but with respect for the limitations I mentioned previously. What I didn't look at is the Steadicam friendly face detection auto-focus, but maybe Michael will let me come into the shop and torture the Saturday crew with the Steadicam Flyer. The face detection feature seems like a perfect combo for wedding and commercial shooters; maybe even some indie filming with a small crew. Many reviewers on the 'net love that feature.
One quick update: The camera we had in the shop previously was a b-stock camera from Sony. Some of you may have noticed my warning about aliasing during over cranking. We received word from Sony that this was a pre-production camera. The camera we have now, a full production model, does not alias while shooting in super slow motion. Woohoo!
If you would like to try it for yourself just give Michael a call at the shop.
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