Any camera position data from the original shot can be used to aid in line-up, but with elements such as water, pyro, flames, or atmospherics that are likely to break the edges of frame, it is best to overshoot (shoot a slightly wider shot), which will allow the compositor a bit of freedom in repositioning the element to best advantage without bits of the action disappearing off the edge of the frame. VFX Directors of Photography often use all of the area of full-frame 35mm or, when possible, VistaVision (43), in order to allow for the most repositioning without sacrificing resolution when resizing or repositioning the image in post.
When it comes to shooting actors in front of blue screen, green screen, or sky, once the correct distance and angle have been worked out to ensure proper perspective, one frequent practice is to select a longer focal length lens in order to magnify the subject. As long as the subject does not break the edge of frame, this magnification yields better edge detail, which allows for easier, cleaner matte extraction. Note in this case care should be taken to avoid the perspective difference of the foreground and background becoming apparent. The intent is still to make the finished shot appear as if shot as one.
Even though there are obvious advantages to shooting elements for specific shots, once the equipment and crew are assembled, one may realize a great return on investment by shooting a library of elements with variations in size, focal length, orientation, action, and lighting. These generic elements can be used as
necessary in building many different shots, scheduled or added.
When shooting either generic or shot-specific elements such as flame, dust hits, atmosphere, etc., it makes sense to shoot some lighting, focal length, and angle variations – sometimes the correct setup ends up not looking nearly as good as some variation shot just in case.
DETERMINING ELEMENT NEEDS
During the bidding and pre-production of a project, the numbers and types of elements needed for various shots are usually broken down and categorized. (44) During production it is common to keep a running list of new elements that are required. Additional elements may be added to the list after a review of the shots in the edited sequence or during the post-production work on those shots.
The first step is to review the list of desired elements with an SFX Supervisor and a VFX DP if at all possible. Their expertise can make things much easier and provide insights to alternate techniques. A skilled special effects person can do wonders with devices they have or with devices they can construct rapidly.
Certainly, elements that require anything potentially dangerous such as flames or explosions will require a special effects person with the appropriate license.
The only hard and fast rule with regard to shooting elements is that they have to look right when they are incorporated into a shot. Since individual elements are shot one at a time, all sorts of tricks can be used when creating them. One can composite together elements shot in different scales, at different frame rates, with different camera orientations, and even with different formats of cameras. An element can be flipped and flopped, played backward, recolored, pushed out of focus, made partially transparent – in short, the VFX Supervisor has an arsenal that includes all of the different types of shooting tricks plus all of the various compositing tricks for creating the desired look.
Even as the bar is constantly being raised in creating realistic digital effects, numerous tricks of the trade of the old school creators of special photographic effects (45) are still valid. To paraphrase Duke Ellington, “If it looks good, it is good.” Some types of atmospheric elements, such as smoke, steam, or fog, can be shot small and scaled up, often being shot overcranked in order to give the correct sense of scale. Water effects can be scaled up somewhat, though issues with surface tension limit the degree to which this works.
Different materials can be used in clever ways. For Star Wars: The Phantom Menace (1999) large amounts of salt (46) were poured over a black background to create the illusion of waterfalls seen in a Naboo matte painting. For Independence Day (1996) a comprehensive library of steam, dust, glass, and debris elements was shot on a single day of thousand-frame-per-second photography. Those elements were massaged in countless ways and incorporated in many shots of destruction. To create the effect of a man whose skin was on fire in a zero-gravity environment for Event Horizon (1997) hundreds of individual bits of paraffin-soaked paper were attached to a specially constructed puppeted mannequin and burned in small groups to create small patches of flame that were not drawn together by convection. For the free-fall sequence in Vanilla Sky (2001), Tom Cruise was suspended upside-down and wind-blown with E-fans while the camera, turned sideways or upside-down at various times, hovered around him on a crane or whizzed past him on a 90-foot-long motion control track.
Miniature pyrotechnics that are supposed to be in space are often shot looking up (or at least upside-down) so that the arc-shaped paths of debris and convection-driven smoke propagation patterns don’t give away the presence of gravity.
It is easier to cheat at some games than others, of course. As humans, we are highly attuned to the way other humans look, and when human elements are shot from the wrong angle, the wrong height, or the wrong distance, even the most nontechnical audience member will often sense that something is wrong with a shot. The cues that trigger this response usually have to do with a perspective mismatch – and the most common error in shooting actors on green screen is to shoot from too short a distance with too wide a lens, resulting in unnatural relative sizes of different parts of the subject.
The best protection against this danger is to line up the shot with the same lens, distance, and angle as was used in the plate shot or as dictated by the action of the shot, but when this is not possible, a decent rule of thumb regarding perspective on a human that is allegedly being seen from a great distance is to get the camera at least 25 or 30 feet away.
(43) VistaVision: a special format camera that shoots with horizontal running motion picture film to provide a large size image equivalent to a 35 mm still camera.
(44) Elements shot for stereoscopic 3D production must be carefully shot with stereo camera rigs, because elements shot “single eye” will often be very difficult to integrate into a 3D shot.
(45) Before the rise of digital compositing and CG effects, most visual effects were referred to as special photographic effects.
(46) Care should be taken when filming any material that may produce dust or small particles. Use eye protection and breathing masks.