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What is Pulling Focus?
Pulling focus is a concept that is relatively foreign to most digital video filmmakers. Often times the only check for focus that a consumer digital videographer will do is a quick look at the LCD screen and that will be it. There is no way that even in the highest level prosumer HD cameras you will be able to do this accurately, and it is obviously impossible on a film camera. To estimate focus there is often a process of "pulling focus," which can mean different things with different video equipment.
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Conventionally pulling focus is the job of the assistant camera person, which is a challenging job. To do this the assistant camera person will measure the distance from the film magazine to the subject meant to be in focus. Then you calibrate the focus on the camera to the specific distance that is there. This is how you can ensure that objects are going to be in focus.
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New Digital Video Focus
This principle can also be in place with digital video as the focus measurements can also be in terms of distance from the camera to the subject. This is really a way of ensuring the focus on digital video as it is not required with digital video. Most of your focus work can be done simply with the image itself. Pulling focus can now mean other ways of estimating and ensuring that focus. The first thing you have to remember here is that you will never be able to ensure focus with the LCD screen or a digital monitor. These tools are good for framing and blocking images, but you will not get a clear enough image to determine absolute sharp focus. Instead you have to use the viewfinder eyepiece to get the image quite right. This should be used in combination with what is called a focus card. This focus card often has a difficult image on it, such as a black and white spiral or other type of semi-optical illusion. This is the best way that you are going to ensure that your image will be in focus.
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Pulling the focus has always been the job of the first AC, and this can be extended along with digital video. The job of the AC will be extended to dealing with the digital storage options that you may be using, such as a mini digital video tape or P2 storage card. The AC has also traditionally just done the measurements and focus changes, but they do not make the changes according to the image itself. This is done by the camera operator as dictated by the director of photography. On smaller productions these jobs are going to have to be united, so the camera operator may do all of these functions. Crew positions always have to be cut on low budget productions, so you have to compensate for that and move away from the conventional order of filmmaking. In this way the focus pulling will likely have to shift to the camera operator for most functions, but it is still going to be important to complete measurements and focus adjustments. The best thing that the camera operator can do is get a clear idea of what the kind of depth of field the camera is capable of and work within that with the measurements.