3D rig
With the help of a 3D rig , two cameras are connected to form a 3D camera system in order to record stereoscopic 3D films and photos.
background
In order to create a stereoscopic illusion of depth, two images with a horizontal parallax must be displayed simultaneously, one for each eye. These can either be recorded sequentially with one camera or simultaneously with two. If moving objects are to be captured, it is important that the images are taken at exactly the same time. Depending on the speed of the object, the tiniest asynchrony can lead to errors in the depth display. This is why two cameras are generally used in photography and especially in film.
In addition, it must be ensured that the two cameras are geometrically correctly aligned with one another. Even minimal deviations from a parallel alignment of the two camera axes to one another lead to an incorrect spatial impression, or to the fact that the images produced cause nausea or headache. The challenge for a 3D rig is that two cameras are connected to each other in such a way that they can be aligned in all axes, but that this alignment is also maintained during movement. For the production of 3D films, the horizontal distance between the cameras must also be changeable by remote control during the recording, so that different recording situations can be dealt with.
There are basically two types of 3D rigs: side-by-side rigs and mirror rigs.
Side-by-side rig
construction
The easiest way to take a 3D image is to place two cameras side by side. The optical axes are either aligned in parallel or can be converged so that they intersect at a predetermined distance. In some side-by-side rigs, the cameras are permanently connected to one another. In addition to the rigs used by hobbyists, this principle can be found, for example, in the GoPro 3D rig and all 3D camcorders, as it is comparatively easy to implement. However, professional side-by-side rigs offer the option of adjusting the distance between the camera axes. It is important that the correct geometric alignment is maintained even when the cameras are moved.
operation area
A side-by-side rig is ideal for long shots such as landscape shots or overseeing sports broadcasts. However, they are unsuitable for close-ups, since the distance between the camera axes must be smaller than the diameter of even small lenses.
advantages
Side-by-side rigs are comparatively easy to build and therefore inexpensive. In addition, they often offer a greater maximum distance between the cameras than mirror rigs. This can be used to achieve a miniaturization effect or minimization and to make even mountain ranges look like a model landscape.
disadvantage
Side-by-side rigs cannot be used for close-ups, as the smallest possible distance between the camera axes is limited by the size of the lenses. For close-ups, however, this distance may sometimes not be greater than a few millimeters. For this reason, mirror rigs are usually used for scenic film recordings.
Mirrory
construction
With a mirror rig, both cameras are aligned with a semi-transparent mirror, a so-called beam splitter. This reflects fifty percent of the incident light. The other fifty percent are transmitted. One camera films the reflection, the other looks through the mirror. Since the cameras are physically separated from each other, they can optically be on the same axis. The cameras overlap in the mirror image and seem to merge into one. In this case, the recorded image is identical. On this basis, any distance between the two optical axes can then be set and the depth effect of the image can be freely selected.
operation area
Because very small interaxial distances are also possible, a wide range of setting sizes can be implemented. This makes the mirror rig best suited for use in scenic films.
advantages
Only through Spiegelrigs is narration with classic film style devices possible. In addition, the option of superimposing the optical axes of the two cameras offers the advantage that the video output can be used for the geometric alignment of the cameras.
disadvantage
The mirror is another optical element that must be precisely manufactured and is prone to dust, stray light and other soiling. The cost of high-quality beamsplitters drives up the price of a mirror rig. In addition, the division of the light for the individual cameras causes a loss of brightness by a diaphragm. Lower quality mirrors often cause different color behavior of the two images, which has to be corrected in post-production . In addition, problems can arise if the mirror filters the light depending on its polarization. This occurs particularly with reflective materials such as metal, leaves and rain-soaked streets.
In some mirror rigs only one of the two cameras can be moved. These have the disadvantage that in steadycam recordings they unbalance the overall system if the distance between the cameras is changed. To avoid this, there are mirror rigs in which both cameras are automatically moved at the same time so that balance is maintained.
Individual evidence
- ↑ http://www.weir3d.de/film/stereofehler
- ↑ a b Max Hemmo (Ed.): S3D NOW! - A Stereoscopic Experiment for Film and TV. 1st edition, Fachverlag Schiele & Schoen GmbH, 2012, p. 218
- ↑ a b Holger Tauer: Stereo 3D - Basics, technology and image design. 1st edition, Fachverlag Schiele & Schöen GmbH, 2010
- ^ Bernard Mendiburu: 3D Movie Making: Stereoscopic Digital Cinema from Script to Screen. 1st edition, Focal Press, 2009, p. 198.
- ↑ Page no longer available , search in web archives: koenig-watzmann.de