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If you have a small DSLR, how do you maintain focus on the subject if, suppose, you are moving it on a mini jib crane or a slider?
The piece of equipment primarily used to focus when camera is in motion is a follow focus. While on a crane or even steadicam, pulling focus can be hard or even impossible. A wireless follow focus will help with wirelessly pulling focus with a separate knob. This takes an extra person and some expensive equipment but will set you apart when the camera is moving while focusing on certain elements in the frame. If this doesn't seem to be an option for your production, you can always set the focus in the general area of action before you start the camera movement. Also, bump up the aperture to achieve a more deeper depth of field so the subjects stay in focus more easily.
October 16, 2014 at 9:49AM
Before you can make use of a follow focus, you need a lens with hard marks for focus range. Otherwise all the focus marks you make wont hold on a still-image lens.
DSLR lens mechanics give priority to being controlled by the camera. They are designed for auto-focusing to one point and snapping a still.
Cine lenses have hard distance marks on the lens and give manual control to the user, or the assistant who is pulling focus. Once the lens reaches ∞, it stops. Likewise, when it reaches near-focus, it also stops. There are no hard stops on most still lenses. They give a little, but then continue to turn thus throwing your marks off.
This is a pretty informative video on the difference between Canon Cine primes and L-Series still lenses. https://vimeo.com/56357604 It pretty much demonstrates how they handle focus in the first 15 seconds.
I hope that helps.
October 22, 2014 at 5:19AM
Keeping focus with a shallow depth of field is tough, so for those shots consider a deeper DOF. Shooting with a wide lens can also help. Of course, these options may not give you the look you are seeking.
November 13, 2014 at 6:20PM
if it's for a shot you can rehearse, then get the actors to go through the shot and put marks on the focus ring of where you need focus to be and then have someone turn the focus at the right times.
Otherwise you can try and use focusing assist if your camera has it. ie: where red lines appear in the camera screen of what's in focus. The sony a7 cameras have it, the cannon dslr's you have to use magic lantern to get it.
November 30, 2014 at 4:03AM
Follow Focus and Dry Erase markers or Gaffe Tape... works for me everytime. If you Can Afford the Cine Lens then get them otherwise work with what you have, find a follow focus kit (Asumming you have a Rig or Rods) and make it work for you
December 1, 2014 at 1:08AM
I recall some film shot on GH2 - it was called Musgo - anyway, they did the low-fi trick of tying a cord between actor and camera op, ensuring that the distance between them stayed the same.
My advice (along with all the excellent tips above) is to try and engineer your shots so that you're not trying to keep focus on the fly. Smooth focus pulling is hard. If you're using cheap-ish modern lenses it's next to impossible. So instead look at ways of keeping the actor and camera at roughly the same distance even when the camera's moving. Shane Carruth did this a lot in Primer - he tended to use circular dolly moves, so although the camera was moving around the actor, the distance between them stayed the same, meaning they stayed in focus (he didn't have a trained DP). If you can, figure out a way of getting the shot as simply as possible.
December 1, 2014 at 2:56AM
Shoot wide! With OIS!
December 1, 2014 at 3:17AM
This is probably blasphemy, but get a mirrorless camera and use auto focus. You can use the focus hold feature to get more accurate results. This is how I shoot on steadicam as a single operator most of the time. Not 100% accurate, but can it can get you there without spending thousands more and/or hiring an AC.
Wireless Follow focus and monitor setup is how its normally done, but as other have said, you need cine lenses as well. That is in the thousands.
Or shoot way stopped down.
December 1, 2014 at 6:15PM
You know it is a nice little community we got going here when nobody has answered..
"I stay focused mainly by taking a couple of deep breaths before I start shooting.. That and yoga..."
December 2, 2014 at 8:44AM
If you maintain a constant distance between yourself and the subject, you should (in theory*) maintain the focus that you set when you first established the distance that will be between you and said subject. As previously mentioned, rehearsing the shot is incredibly helpful here. Also, stopping down (increasing the f-stop number of your aperture) will aid in giving you a higher range of what that distance can be. Happy shooting! -George
December 3, 2014 at 7:00PM
Do you know how use follow focus? is with marks. You must practice before.
January 20, 2015 at 5:03AM