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December 07, 2019, 12:03:34 PM


Author Topic: AF to MF while filming  (Read 4709 times)

Offline DanceVideoTV

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AF to MF while filming
« on: February 06, 2013, 08:49:41 AM »
Im not new to photography or or videography, however, I am new to DSLR cameras. I'm pretty savvy with technology and I learn quick, I learned how to use MF when shooting photos, but Im interested in learning how to use I guess you would say transitional focus during filming. By this I mean Im shoot my subject whose center stage everything else behind them is blurred, another subject walks in from behind and the focus switches to that person and everything in front is blurred. Any help would be greatly appreciated! Also on a side note, is there any way to silence the sound the lens makes when focusing during filming? Or is that something I would just have to edit out?

~Thanks

Offline ctyhntr

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Re: AF to MF while filming
« Reply #1 on: February 06, 2013, 03:42:34 PM »
The technique is called rack focus, changing the focus during a shot.  You can google follow focus, as they range from $5 gadgets and up.  If you're manually focusing check to see its switched off from AF,  autofocus motor shouldn't be engaged.  For cleaner audio, you may want to look into external mics (shotguns and lapel), or a separate audio recorder and add the sound back during editing.

Offline AndyCivil

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Re: AF to MF while filming
« Reply #2 on: February 06, 2013, 05:20:54 PM »
Everything ctyhntr said. There's a wikipedia article under http://en.wikipedia.org/wiki/Follow_focus

Pros don't use autofocus when filming. They'll generally plan the shot, often mark the focus point on the puller (see the Wikipedia article) and do it manually.

Offline DanceVideoTV

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Re: AF to MF while filming
« Reply #3 on: February 06, 2013, 06:26:31 PM »
Thank you both! I do have lens with MF and AF, obviously I would use MF, but Im not quite sure how on my camera I would control when what it focuses on other then setting up the initial shot, but once I begin filming Im not sure how I can switch my focus?

Offline DanceVideoTV

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Re: AF to MF while filming
« Reply #4 on: February 06, 2013, 06:29:54 PM »
Upon re-reading that article, I think I may be a little confused perhaps. Is a focus puller an actual device? Or a technique?

Offline AndyCivil

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Re: AF to MF while filming
« Reply #5 on: February 06, 2013, 10:51:05 PM »
The T2i isn't going to help you much to do this, to be honest. Its autofocus features are that when the switch on the lens is set to AF, it will focus when you half-press the shutter (*) according to your settings, the type of focus (quick, servo) and which focus points you've chosen. You don't want it to autofocus while you're taking a movie because it will search and hunt for the best contrast - i.e. mess up your video. The sound will come through, too.

(*) Some smart ass is going to say "what about back-button focus?", but let's keep things simple, OK?

So basically, you need to manually change focus for your 'focus pull'. A 'focus pull' is an instance of the technique in your movie. A focus puller could be a lever or rack attached to your lens to help you do it in a controlled way (trying to rotate the lens with your other hand is bound to introduce some sway, LOL) or for a pro setup, it could be an assistant dedicated to changing the focus at the right moment, possibly aligning pre-planned marks on the device.

Professional focus pullers are a bit expensive, we've talked about DIY devices before; you can search for them on youtube. I've got a jar opener made by Trudeau which does work, unfortunately it's awful with the cheap wide-aperture lens that everyone wants to use it with (the 50mm ƒ/1.8) because the focus ring on that lens doesn't lend itself to having a rubber ring wrapped around it.

Also, the T2i only provides a basic mono microphone on-board. They expect that anyone serious about video will attach their choice of stereo mic to the input jack. Another slightly amateur feature of the T2i is that you can't shut off the auto-gain on the mic; this is one of the things that Magic Lantern does rather well; I think it's one of the 'killer apps' that push people into installing it.

I put a 'focus pull' in my squirrel video; I wanted to zero in on the paw marks on the window. I started a clip in focus, then manually turned it out of focus; then I reversed the clip in the video editor.


Offline DanceVideoTV

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Re: AF to MF while filming
« Reply #6 on: February 07, 2013, 07:21:14 PM »
Thank you so much! Im still a little bit fuzzy on this topic but you guys gave me great reading material and research to work with! I do have my own external mic so that wont be a problem. Thanks again!

Offline 1074

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Re: AF to MF while filming
« Reply #7 on: February 13, 2013, 11:55:55 AM »
A focus puller is a person who uses a device called a follow focus to manually change the focus of the lens, live, while recording.

An acceptable alternative to using a follow focus rig exists, but it's kind of risky, and I only recommend it to advanced operators.


You place your fingers gently on the focus ring of the lens, and then....   you turn it.   :o
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