Question, zooming and autofocusing?

[stevet1]

If I am zooming while filming, and I am in an AI focus mode, do I keep the shutter button down halfway, or do I leave it alone and let the camera take care of re-focusing?

Should I keep the camera in single shot mode?

Thanks,
Steve Thomas

 

[VidThreeNorth]

What camera is this?

 

[stevet1]

I am using a Canon Rebel T6. I went back and re-read the manual, and I don't think I can reconcile autofocusing and zooming at the same time.

To paraphrase the manual,

Auto Focus during shooting:

"AF is possible during movie shooting using the shutter button, if you enable it in the Menu. However continuing autofocus is not possible. If you autofocus during movie shooting, the focus may be thrown off momentarily or the exposure may be changed. The movie will also record the lens operation sound. During movie shooting, if the AF method is set to Quick Mode, AF will executed in Flexizone-Single"

I took several test movies; with and without AI Servo, and with and without using the shutter button to autofocus, and they all turned out crap. I think my best bet will be to make several, what Canon calls, Video Snapshots of 2-8 seconds each, and string them together into an album.

Zoom (manual on my lens) - autofocus - shoot short movie. Re-zoom.

Repeat

I also disabled the sound recording for now. That was really annoying.

Steve Thomas

 

[zombiesniper]

If you are using the shutter button to auto focus you can half press the button for auto focus to continue to work in video mode. If you are using back button focus you can have the button depressed for auto focus.
Now if you are doing this I highly recommend using a single focus point. Don't let the camera decide what to focus on.

OR

Use the touch screen to set the focus point and the camera will try to maintain focus on the selected point.

Shaky movement, quick panning or rapid zooming can also cause your focus to go out.

 

[VidThreeNorth]

I have not used that camera, but I can say that in part it is also going to depend on the lens. Many still camera zoom lenses will allow the focus to drift wildly during zooming based on the assumption that a still photographer won't care as long as the camera finds the focus again fast enough when focus is activated for the next picture. But that means that as you are zooming, the focus might need fairly extreme compensation to maintain focus, and it will vary depending on the lens. If this is a "money job" then you might even want to rent a proper cinema zoom lens, and that will probably be a fully manual lens.

Another answer, if it is a "money job" then you might think about accumulating specific shots and then renting a good camcorder for a day. That opens a different set of problems if you have no experience with camcorders. The "Pro-sumer - to - Real-Pro" stuff will not be familiar to someone coming from a DSLR.

 

[TWX]

The nature of the behavior will partly depend on if the lens is parfocal or varifocal. Parfocal is arguably best since the lens remains in-focus as it is zoomed in and out. Varifocal lenses do not remain focused when zooming.

Now that said, not all varifocal lenses are created equal. Some varifocal lenses aren't strongly so, such that the camera can keep up autofocusing as the zoom changes without it being particularly noticeable. Other lenses that suffer strongly will probably lose focus as one zooms.

I found the 18-135mm nano USM lens with the power-zoom module does a pretty good job managing to refocus as one zooms. It's not parfocal but it's not horrid either.