Accelerated (rapid) filming, in frequency exceeding the standard (24 fps), is used to create the slow motion effect, which is in demand in the projection of films, television, computer games, scientific cinema. It is used to capture sports events, to reproduce the movement of the elements of the layout or natural phenomena in accordance with the established time scale. The screen shows an imaginary slowdown of the recorded phenomena, and the viewer is given the opportunity to consider the intermediate phases of the processes and poorly distinguishable details.
Features of fast shooting
Types of shooting:
- accelerated or rapid shooting (32-200 fps) is carried out using standard equipment with a clamshell mechanism and intermittent movement of the film;
- faster shooting at a frequency of 200-10,000 fps is ensured by continuous uniform motion of the film using optical and electronic methods of manipulating light. Accelerated shooting is carried out from the hands of a moving vehicle using professional or conventional amateur equipment with an extended frequency range necessary for image stability.
Filming technologies have remained almost unchanged since 1955, with the exception of creating an electronic shutter, although the image is currently not captured on film, but on a sequence of digital matrices, which ensures a frame rate of 100 million per second.
The degree of acceleration is limited by the capabilities of the camera, its design and dynamics. For amateur equipment, accelerated shooting is characteristic - 64-72 fps, for professional - 360-600 fps. Modern cameras are able to provide a frequency of 200 fps with its gradual increase in order to obtain the special effect of speed increase. If you need more acceleration, then resort to the manipulation of frames on film.
Frame frequency
There are various types of filming in scientific and applied cinematography, in particular for the study of fast-moving phenomena and processes. One of them is high-speed, or rapid shooting, with a frequency of more than 250 frames per second, which allows you to capture processes that are inaccessible to the human eye because of the short duration or high speed of the phenomena.
Among the objects of research you can include:
- the movement of living creatures: the frame rate is from 100 to 300 fps, shutter speed - 1/1000;
- the functioning of mechanisms (1-10000 fps);
- destruction and explosions (10-100 thousand fps);
- shock waves of gases (100 thousand - 1 million fps);
- electric discharges (10-100 million fps) and the like.
Technique
Due to the variety of conditions, a wide range of technical means and variety of frequencies, professional video shooting of high-quality objects is possible. High-tech equipment in addition to standard image processing mechanisms also uses optical accelerators, high-speed shutters, electronic and optical converters.
High-speed photography is usually carried out using pulsed light sources (gas discharge lamps, explosive light sources, spark gap with air gap).
Chrono-photography is an intermediate way between photographing and filming of capturing successive phases of phenomena using a rotary slit shutter. The resulting images are layered on top of each other and combined into a single tape. The method is used for continuous movement of the object of observation. Unique effects are provided by an open lens with pulsed lighting.
High Speed Movie Methods
- Intermittent moving film is captured at a frequency of 600 fps using a mechanical film transport system.
- More accelerated shooting at a frequency of 1000 fps is realized using pneumatic devices or with the mobility of the film due to the elasticity of the loops that form behind the film channels.
- To achieve higher frequencies, moving photosensitive materials are used.
The effect of sharp images of successive transformations is possible when the film is shifted relative to the object in the following ways.
Electronic switching
A method in which gap seals cut off limited time instants to expose a frame. For the shortest period of time, the frame offset relative to the optical image does not exceed the permissible blur of the negative. It will require intermittent lighting with pulsed flashes (lasting 10-7 fractions of a second) or a shutter located in front of the frame connector like a shutter, but instead of a cutout there may be a miniature slit (one or several).
Optical switching
If accelerated shooting involves a still image with respect to uniform motion of the film, it is necessary to neutralize the displacement of the light-sensitive material relative to the image in the interval of exposure of the film by moving the light-reflecting optical system, acting with speed and in the direction of movement of the film.
To implement optical compensation, a mirror polyhedron, a glass plate, or a prism in motion are suitable. The size and position of the optical element must ensure that the linear displacement corresponds to the movement of the frames. The film should be located on the surface of the polyhedron in a special channel of the film. The method is used for low-volume processes.
The limit of frequency increase during electrical switching is limited by the possibility of reducing the interval between flashes, and with optical - the speed of rotation of the shutter disk and its diameter.
Projection Slow
For visual viewing on the screen, slow motion is used, which is possible both with an increase in the frequency of filming, and with a slowdown of the motion of the film in the projector.
The disadvantage of this method is the apparent discontinuity, and some high-speed processes generally fall out of sight, hiding between the captured frames during the shooting. If the deceleration is more than 1 fps, the demonstration of the image resembles a slide show. Therefore, the optional slowdown is more often replaced by faster shooting.
Modern filming techniques
- Modern cameras are equipped with an electronic stabilization system, but still high-quality accelerated shooting is created using an adjustable length support, a "monopod" to ensure image stability without jitter.
- The vertical objects and the sides of the frame must be parallel.
- Video techniques such as alternating close-ups with small and medium ones are considered good style. Overuse of the zoom system tires the viewer, so it’s better to sometimes stop recording, transfer the shooting to the desired scale, and then continue.
- A plot of about 5 seconds is considered the most optimal duration for perception, a maximum of 12 to preserve the vivacity and dynamism of the footage.
- It is recommended to set the white balance in an artificially lit room manually.
- The horizon line is not the last characteristic that professional video shooting is distinguished for: it should take place at the level of the middle line of the viewfinder or slightly higher. Scenes in which the upper part of the frame is occupied by 2/3 of the celestial space are perceived with tension.
- To give volume to medium and large-scale frames, an object can be placed in front of the lens that unobtrusively creates an idea of the depth and scale of the image.
- When choosing a shooting angle, various perspectives should be considered, going beyond stereotypes, for example, showing an object from the side of the audience and “judges”, as well as through the eyes of an outside observer. And each such step for the operator is a new round in his skill and a new discovery that raises his level.
We should also mention professional ethics: during large events there are not so many advantageous positions that are suitable for a successful shooting, so you should take care of all the necessary conditions in advance.