I don’t believe in autofocus for video. It can’t work. I doubt it will ever work in the way I would want it to work.
That’s a bold statement to open this post with. Let me explain. For my entire 25 year career it’s been manual focus all the way for a reason. Manual focus works, well, it works as well as the person pulling focus, and 99.9% of the time that is me. My brain knows what I want to be in focus within my frame. My brain knows when to keep something in focus and something out, no matter what the composition. My brain knows exactly when I want to pull between certain things at a certain speed, changing speed, perhaps even going back. The options are infinite…simply down to what I see travelling down the optic nerve to the cerebral cortex where the decisions are made triggering impulses that travel down my spinal cord through the motor neurons for the appropriate muscles and releasing a chemical which then causes my muscles to react in a way that hopefully keeps my shots in focus…see EASY!!! 🙂 Not much for a camera to replicate then?!
OK…auto focus in stills cameras…it works, right? Why? Because you move the camera to get what you want to be in focus, half press the shutter, then adjust the composition and fully press down to fire the shot. You simply cannot do this in video. Fine for stills, where you temporarily re-frame before locking in the composition, but for video you are rolling the whole time. Sure, on some cameras you can do this before you hit record, but once you are rolling, that focus is in your hands. You can’t then keep moving the frame back and forth to select your focus. This is one shot auto focus, each time you press the button to get focus a new point is found and held. This is no good for video. Video needs to be continuous auto focus.
Getting focus correct is even more critical than nailing exposure. After all, with the raft of raw camera, incorrect exposure can be fixed, to a point. Out of focus shots? Well we aren’t quite at the point of cameras having the Lytro technology in them yet…one day. Out of focus of course is unfixable…now in focus? Yep, that can be made out of focus in post!
Explaining exactly how the different auto focus systems work is very complicated. I have tried to simplify it in laymen’s terms, but it’s well worth reading the countless articles online which explain much better than I do below how they work!! After all, I was not that knowledgable about it until I had to find out about it!
Pretty much all video, and many stills cameras, use autofocus via the contrast method, picking a single point in the frame. Generally a small part in the centre. This is a passive method. The sensor is searching for the maximum intensity difference between adjacent pixels. When stuff is blurred/out of focus the contrast is minimal, as it all blends into one. When the shot is in focus the contrast intensifies. This is when the sensor thinks it is in focus. That’s why, when you try to get autofocus lock on some clouds in the sky, it will struggle because the contrast is so soft. You need something hard at infinity to grab it then reframe. The single biggest issue with contrast autofocus is that it won’t know it’s in focus until it’s gone past the correct focus point, realizes that it’s getting blurrier, and comes back again. It’s always checking…just to be sure! The dreaded “hunting focus”! 🙂
Autofocus for DSLR stills is more complicated, as almost all use phase detection which is faster and more accurate. It’s also done via multiple points, not a single point like in stills. Roughly putting it, they use a mirror which splits the light differently so it can quickly and accurately measure differences to get focus. Phase detection autofocus (almost always) needs a mirror though. When you shoot live view with these DSLRS for stills, naturally the mirror flips up and you are just using the plain old contrast method, which is slow. That’s why I am sure anyone who has taken a photo with a DSLR “properly” and then in live view mode can attest to the huge difference in speed.
You don’t actually have to have a mirror to get fast auto focus though. Sony for example have been at the forefront of hybrid autofocus technology using contrast & phase detection with their Alpha line of DSLRS for some time, and now with their mirrorless stills cameras they are surpassing what mirrored cameras could do. It’s still phase detection like mirrors, but replicated on the sensor itself with dual pixels, adding in contrast too for the best of both worlds. In fact the soon-to-come-out Sony Alpha A6000 is stupidly fast with a speed of 0.06 seconds to nail that focus and 11 frames a second capture! It’s all super high-tech, and if you really want to learn more, I am sure a bit of searching can yield a white paper for you to read!
The one other main type of focus is called active auto focus. It’s something done externally by the camera to help it get the focus. Sound waves have been used in the past. Nowadays many compact cameras (and in low light) DSLRS emit a light beam, mostly infra-red, to know what is in focus.
Naturally, active is not used in video as a light shining on something is not conducive to a great shot! That is why contrast has been the one used for video.
Auto focus is not at all new in video cameras. I think my first video camera, an old Sony Video 8 Handycam from 1987 had it…every single consumer video camera I have owned pretty much has had some sort of auto focus in it. I have always turned it off!
The only one I have had relative success with is facial tracking continuous autofocus.. I first came across it on the Panasonic GH1 with the excellent big range kit lens. In fact the first thing I put out with the GH1 was shot almost entirely with auto focus. That was almost exactly five years ago! It recognises a face, puts a square round it and keeps following it…you could even tell it to just follow that one particular face. It sort of worked, but I think cameras just think we all look alike 🙂
Of course, keeping focus in small-sensor camcorders is a lot easier due to a much deeper depth of field, and that combined with standard definition let you get away with a lot. But with larger sensor cameras like 2/3″ broadcast ones and then with High Def, your mistakes were easier to see.
Now so many of us are shooting on big sensor cameras, Super 35mm and full frame, keeping moving shots in focus has become a nightmare. Static shots? Fine. It’s that movement that kills us, plus all those lovely DSLRs that changed everything didn’t help us at all with their lack of focus peaking….oh and of course now there is the move to 4K? This really does separate the men from the boys..and yes I am often reduced to being a boy on some occasions. You simply have to stop right down and/ or use EVFs or monitors with peaking.
Another massive contributing factor is that most of us are still using still lenses for video. The majority of these have rather short focus throws, which means it can sometimes be incredibly hard/ impossible to follow a moving object/ person accurately when the movement on the barrel is sometimes so miniscule.
How many of you own F1.4 lenses? Shoot wide open a lot? Gave up on moving objects and stopped down? Of course you did…well you should have done!
I consider myself to be pretty good at keeping stuff in focus manually, even quite wide open, but that is only due to a lot of practice. I screw up a fair amount of times still. It’s just too bloody hard on some shots! Human error is the most common reason for me doing another take, not an issue with the equipment.
So FINALLY this brings us to the C100 auto focus upgrade. Something I read about and dismissed about as fast as I read it. After all, I had the 70D and that has the dual pixel CMOS auto focus tech in it, and I had never been inclined to use it. I just really had no interest in it. I don’t like video auto focus. So even though I am an owner of a C100 (and C300) I moved on. It was only when Canon USA contacted me in late November about it did I put it back on my radar.
They wanted to hire me to test it out for them in a number of scenarios. I made it very clear straight away about my dislike for auto focus in video, I actually think they considered my opinion a benefit for this job! They wanted me to try it in different configurations and see how well it worked and then tell them on camera what I thought…
That’s caused two problems for me. Firstly if I agreed to being interviewed about it, what would happen if I didn’t like it? I would only be 100% truthful. Would they really want that from me? Secondly I didn’t want this to then become a paid endorsement of something I had never used, had no interest in using, and had no plans on getting. Ethically it was not good.
I asked if I could try it out first on my camera before deciding anything. With it being so new, that was not possible. There was at the time I think 1 maybe 2 cameras in the US late December/ January with the firmware. So they were going to send me a camera with it to try out to see what I thought. Unfortunately it didn’t happen. Due to my schedule and CES (where the camera was) getting the camera proved impossible. They knew of my strong ethical concerns about this and were very respectful of them thankfully.
This is what we agreed: I would be in the Miami right at the end of January for 10 days for a job anyway and on the day after I got in from London, they would give me the camera and let me test it out fully…whilst filming me. Afterwards they would interview me, warts and all, about exactly what I thought. I warned them it might not be pretty! If I hated it passionately I am pretty certain they would not be using me in their video! 🙂
For me there are two types of shooting where if it worked, autofocus could be very useful. Firstly where you couldn’t touch the lens…steadicam/ glidecam/ movi type devices. Secondly, wide open shallow depth of field, where human error isn’t too likely to get good results.
So there we go. I was going to shoot on the gorgeous Movi (a piece of gear I have had for a few months and have gotten quite good at, but mostly have to use in single operator mode which is very limiting due to focus issues. You really need a focus puller!) , some hand held wide open shots and some tripod shots.
You will understand more once you watch the video below but one of the biggest issues for me was the limitation of the auto focus area just being that small square in the middle. Never in every shot are you going to want your focus to be dead centre. The key to getting good results with the continuous autofocus, is clever use of the focus lock button, which I programmed onto function 7 in the photo below. I demonstrate it in the C100 autofocus video below.
The problem I had, though, was I wished I could have used it during the Movi shooting. I simply needed the ability to press the button. What is needed is a Zacuto Grip Relocater. You unscrew the side handle, run their extension cable to the grip holder which would be on one of the handle bars of the Movi and you would be sorted!
So what do I think? Am I a convert? Well you see the results in the video below that Canon USA put together. That there is a video at all says a lot!! I went from skeptical to marginally impressed, to frustrated, to very impressed…at times.
It is definitely a tool for your arsenal. Something you may never use or something you may use all the time. Depends on your style of shooting. It’s not cheap. It’s $500 in the USA (via this link) 400 euros or £340 (plus VAT). You may complain (and I hear you) that it’s a lot of money for a firmware upgrade, for something that was already in the cameras, but it is more than just new firmware. The sensor is re-calibrated to make sure the phase detection is working accurately. They had put the technology in there when the camera was made, and at that point were not sure if or when they would actually be able to make it work well enough to enable it. Hence the camera has to go back in to be made 100% accurate.
The other good news is the C300 will be able to get the same upgrade in May with the C500 next I expect. Don’t expect my beloved 1DC to get the same treatment, as it has a different sensor to the other C cameras which all share the exact same sensor. Shame…it really needs it, as it has no focus peaking…there is a point! If you can’t give me autofocus on my 1DC can I have focus peaking please? 🙂
The C100 is an excellent budget S35 video camera. It has so much going for it. A wonderful image, nice form factor, great LCD, amazing low light. It’s not perfect, but it is $5000. For a Super 35mm HD video camera, that’s pretty damn good. You can see my review of the camera at the bottom of the post…it was done last year before the autofocus of course.
Am I a convert? I would say yes…I am impressed enough to be booking my C100 in when I get back from NAB and also my C300 in May. How much will I use it? No idea. I think on the Movi I will use it a fair amount actually. That’s why it’s a shame it won’t be on my Movi camera of choice, 1DC. At least my C300 will have it, and this feature with the Zacuto grip relocator could be the answer to my one man 3 axis brushless gimbal problems!!
Just in this iteration I really wish we could move the area to be measured ourselves, and also change the reaction speed of the autofocus. Fast works well, slow also works well at times!
Going back to my opening paragraph about I don’t believe it will ever work the way I want it to, why is that? It simply cannot read my mind. That is what autofocus needs to do, to understand what I want in the frame to be in focus etc…Once we have that bluetooth implant for the cerebral cortex available, we will have the best of both worlds! Mind reading autofocus with mechanical precision…then again will my mind deliberately make the autofocus no longer work as well? Perhaps it will be trying to replicate the (flawed) human touch…in which case we are back to square one…
STOP DOWN! 🙂