Auto Focus Video Camera

[Mahesh Patel]

Hello - Is there a camera that will shoot HD video on auto focus?

I want to just mount the camera on Glidetrack or Glidecam and off it goes.

[Brett Sherman]

There are lots that auto-focus. In the DSLR world it's the Panasonic GH2. Canon's do not. Supposedly the upcoming T4i might have it. But who knows if that's true or when it is happening.

[Justin Molush]

Unfortunately, in the DSLR world you are stuck with manual focus unless you go the panasonic route where I hear it is alright, but obviously not up to par with a true video camera.

DSLRs autofocus is optimized to run through a different AF method than what you use when in video mode or live view, which is purely contrast detection. The AF of these cameras also hunts extremely quickly back and forth to find focus, and that is something that must be eliminated in video for it to be viable. On top of that, internal audio goes to crap when the lenses focuses even with USM/HSM lenses. you can still hear the whirring and the servos turning on and off.

I wouldn't hold your breath for it, but it would be a pleasant surprise in future releases.

[Kin Lau]

Yes, the m43 DSLR cameras all do as do the Sony SLT series, which are true SLR's with phase-detect AF and a stationary mirror.

I've use my GH1 with a monopod acting as a cheap steadycam type balance, and used the AF on my 14-140 for a few glidecam style shots. DOF is so deep on the wide shot, that you can't really tell if anything wasn't in focus.

[Nigel Barker]

Professional Steadicam operators use a wireless follow focus & have a camera assistant pulling focus for them (they may also be remotely zooming & adjusting aperture too). What us amateur Steadicam operators do to cheat is to use a wide lens & stop it down if necessary then focus at the hyperfocal distance for maximum depth of field. For instance with a 17mm lens on a Canon APS-C DSLR at F/5.6 the hyperfocal distance is 8.88 ft & everything is in focus between 4.7 ft & infinity. Online Depth of Field Calculator

[Chris Harding]

That's a neat calculator Nigel!! Now is there any way that you could calculate the circle of confusion for a video camera with 3 x 1/3" chips????

It would be very useful to know (even roughly) when my camera is at full wide (3.9mm focal length) what sort of DOF I have at a few common distances!! The calculator only lists still cameras.

Actually I mistakenly grabbed my A-Cam at a wedding ceremony with the lens in manual and set around 15' and put it on the stedicam and did a full 15 minutes with the couple and I was surprised that everything was pretty sharp...it was a bright day so the iris was small which also helped!! So a DSLR at F16 on a stedicam with the lens set around 5' is really going to be pretty sharp as long as you don't try any big closeups!!!

Chris

[Nigel Barker]

Chris, the 3 x1/3" chips are one each for R,G & B so for DoF it's the same as a single 1/3" chip CMOS camera & if you scroll down on that calculator you will find that it's not just stills cameras listed but also real cinema cameras using film plus camcorders with various size sensors. For a 1/3" camcorder with the lens at 4mm even at F/1.7 you can see that when focused at 15 ft that the DoF stretches from about 2 ft to infinity while at F/11 it's from about 5" to infinity!

[Chris Harding]

Thanks Nigel

I made it a favorite!! It would be a useful tool on the upper zoom ranges .. in full wide unless you are poking the lens hood into someone's nostril you are unlikely to be out of focus on a stedicam!! I would say that our OP could quite safely put his cam on the stabilizer, and at F11 or F16 and a general focus of a few feet he could run around without too many focal worries!!

Chris

[Mitch Holland]

Check out the free android app "Acacia" too. You set it up to save your cameras and lenses, then it shows you DOF calculations. A bit confusing at first, but pretty cool once you figure it out.