Why didn't Canon include continuous focus?
 

I love my 7D, but I'm rather dissapointed that it won't continually focus when shooting video. Afterall, even the cheapest video cameras have this ability, and have for years.

Was the function crippled, or are the lenses just so different? Is it possible that someone like Tram could add this functionality in a custom firmware?

This is how autofocus works. This might give you an idea of why it's not available on the 7D
HowStuffWorks "How Autofocus Cameras Work"
I would also say that there are many camera makers who would rather not have an active autofocus going on. Manual everything gives you more creative control.

I understand there are benefits to manual focus at times, but on a camera in that price range, if it claims it can shoot video it should be available. Their commercials even show it being used to shoot sports.

All this cameras have a small sensor = wide deep of field.

But i knew no camera with big sensor = small deep of field with autofocus - even high price cameras have not this ability.


If you use a camera with small DoF to make movies you use them because you will work with focus - and no AF can knew what Part of the picture you want in focus.


Daniel von Euw

Remember, the 7D is in the first place a still camera. The video comes as an 'extra'. The use of video in still camera's is in the development phase and come time more functions and ease of operating will progress to a more friendly level.

When operating in Live View mode for video recording, a Canon D-SLR switches to contrast detection for its AF function. The fact that it is not capable of continuous AF in this mode is definitely a limitation of the system; however, the camera is built first and foremost for still photography.

I don't think firmware can change the operational mode of the AF system when the mirror is locked in the up position. It's not "crippled," it's just the way that a Canon Digital SLR is designed to work. Despite their ability to record video, these are hybrid systems which should not be expected to operate in the same way as a proper video camcorder.

For more information, see my notes at Canon D-SLR still-photo cameras... don’t allow for continuous AF in movie mode

Pro Cameras don't come with Auto Focus for a reason
 

No pro level camera comes with auto focus.
There is no system that provides better focusing ability than the operator and an assistant.
I don't want my camera deciding what I want in focus, that's what I get paid for. Try doing a pan across multiple objects and keep focus from going crazy with auto focus. Good luck with that. It's even more critical with shallow depth of field. The camera just isn't going to pick the right spot to focus on.
If you feel that you need auto focus, get an assistant to monitor your focus and pull focus as needed.

Maybe you should call Panavision or ARRI and complain that their $250k+ cameras should come with autofocus at that price. Or call RED, TGV (Viper), Silicon Imaging, or Sony's Cinealta group and tell them that their $80-150k cameras should come with autofocus as well.

At the level of the game the 7D is emulating, AF simply doesn't exist. And pros at that level don't want it either.

For what it's worth, the forthcoming RED Scarlet 2/3" version with an integrated 8x zoom lens will indeed have autofocus, and there are plenty of broadcast video lenses that feature continuous AF or momentary AF (however, none of them are built for an APS-C sized sensor)

The limitation of the Canon D-SLR series has more to do with the way Live View works than anything else -- these cameras are optimized for still photography, not video.

True, but 2/3" is not APS-C nor is it 35mm. And at those sizes, I am unaware of any pro cams with autofocus. I am also unaware of any AF PL mount glass.

Thanks for all the great info. Daniel and Chirs, your points were especially enlightening. I wouldn't mind manual focus if I could look through an eye level finder, as on ENG cameras, but even with the Hood Loupe, it's not comfotable for me. Maybe I need more practice too.

I also had not considered the technical difficulties the larger sensor provides. I thought it was just a marketing decision.

You'll note that the people assigned to do focus on digital cinema cameras are generally working with a very high quality LCD panel attached to the camera. I'd highly recommend you look into this option. It makes the focusing quite a lot easier. Perhaps something from Marshall or IKAN.

When shooting run and gun, DSLR focus will be always be difficult, relative to the user’s ability obviously, but it won't be easy.

And these DSLRs we have now require very precise focus, too much IMO, just as a normal motion picture camera does... and motion picture cameras have AT LEAST two operators parked beside 'em.

For narrative, scripted shots:
If you can find a way to view a monitor, and what i have been doing is, putting a thick elastic band around my focus ring. I can mark it with a pen to precise focus points. Have my talent stand on certain points, mark the lens at those points and voila. This is the way its been done for..ever!

Something else I do is, keep my monitor in front of my lens. That way I can view the monitor and the lens simultaneously. My cinematography teacher taught me that one long ago. Ideally, having a focus puller and an operator would be perfect!

Every situation is different: adapt, enjoy!

When shooting with a DvSLR, the editor is your friend. Show the shots where you nailed focus. Skip the shots where you didn't. For narrative, this might mean lots of takes and taking the time to review the material on a good monitor before striking any setup. For documentary, this might mean that you have to cut some shots from the final edit that you really wish you had nailed.

One of the most impressive videos that I've seen for nailing focus is the SEC Championship Game video. It was shot with a Cavision finder, a monopod, and very fast 200mm and 400mm IS lenses. I'd bet he dumped a lot of footage in the bin, but the stuff he kept is marvelous.


Here's the associated "making of" video

Hey Jon
Thanks for posting that. I'd not seen it before and found it really interesting. Well worth watching.
Thanks