6.1) Rotational capture.
6.2) Tangential capture.
6.3) Side by side capture.
6.4) Side by side single camera capture.
6.1) Rotational capture.
Rotational capture is pure illusionism, because we are going to deceive our cerebral cortex by showing two images with a different parallax captured with a single camera ahead of the NPP. In a way that what we are doing is to take advantage of the parallax perception of a Cyclops to generate two different images, but let’s not forget that Cyclops sees in 2D.
In the case of “Google Jump” 16 cameras are used, which indicates that there is a camera every 22.5º.
If we make this capture from the photographic point of view, we will say that the “off-set” of the entrance pupils with respect to the NPP of the RIG “Its geometric center” is 13cm, and as we are going to use a rotation of 22.5º to take 16 photos, we will be using an interaxial distance of 4.5cm.
Many years have passed since the Jump project was presented and now the VR cameras have reduced the number of optics by expanding their FOV above 180º, so the Kandao Obsidian uses only six cameras, one every 60º and with a diameter of 143cm, so its interaxial distance is about 6.5cm and its safety distance is about two meters.
It is interesting to know that using a rotation base of 60º, the “offset” that we use will be equal to the interaxial distance, since an equilateral triangle is composed by three angles of 60º, and for this same reason if we use a rotation base of 30º, 12 photos, the interaxial distance will be equal to half of the “off-set” used.
“We the photographers have the freedom to choose the “offset” and the number of photos to take, which allows us to calculate the interaxial distance to adapt it to each scenario, or for special scenes in which we have to capture very close to walls or objects of the composition”.
The minimum number of photos to make a rotational stereopanorama is six, but if we make 8 like the “Insta Titan” the stereoscopic quality increases generously, and if we take 12 photos using a 30º rotation base we will obtain a stereoscopic quality a little closer to the one we obtain capturing side by side.
In the following table we see the off-set equivalences and the number of photos with the interaxial distance.
We will use a 45º rotation base (8 photos), in small interiors and the 30º rotation base (12 photos) in large interiors. This technique cannot be used outdoors, except in special cases where the wind is zero.
6.2) Tangential Capture.
The tangential capture is an evolution of the “rotational” capture that solves the stereoscopic fall in the seams, obtaining a result with a stereoscopic quality much superior to the “rotational” technique and very similar to the capture side by side, but still without reaching its plasticity.
It is important to emphasize that this technique is only valid for photography and it is not possible to construct a RIG video using this configuration, since the bodies of the cameras force to occlude the captured image.
The capture is done by means of a 30º base rotation, 12 photos that we can take in a single row if we use 8mm, or in two rows if we use 10mm optics.
In the following graph we can see the difference of configuration between the rotational and tangential capture. We can see that the only difference is that in the rotational the optical axis is aligned with the radius of rotation, while in the tangential the axis of the camera is rotated 90º with respect to the radius of rotation.
This photo was taken using a 10mm Alpha 6, so that in each of the 12 positions (30º) a tilt of +- 45º has been made. A simple glance with anaglyph glasses shows that the stereoscopic quality of this technique is much better.
6.3) Side by side using twin cameras.
Side by side capture is done based on traditional stereography, placing two twin cameras side by side, resulting in a more natural stereography. It is important to place both cameras as close as possible to obtain the minimum interaxial distance, which we will obtain using Sony’s Alpha 5 series that will allow us to mount at 6.2cm, or Sony’s Alpha 6 series with which we will obtain an interaxial distance of 6.8cm.
Pseudo-nodal alignment is performed by matching the NPP of the RIG with the midpoint of the hypothetical segment that joins both entrance pupils.
The main advantage of this system is its freedom of movement in two axes, which allows us to make two rows, even using 8mm, to obtain a correct stereo superposition in Zenit and Nadir. This system will also be necessary whenever we use optics of 10mm or higher.
The lower supports can be moved laterally, This function allows us to join both cameras until their physical contact, obtaining the minimum possible interaxial distance, and at the same time allows us to work with hyperstereoscopic interaxial distances, simply separating their optics more than 7cm.
If we want to work with hypo-stereoscopic interaxial distances, we will use only one camera and we will nodally misalign it at half of the chosen interaxial distance.
In short, an economic and multifunctional solution that will allow us to work in any type of environment, with any type of optics and sensor.
6.4) Side by side, single camera capture.
Working in parallel with a single camera implies duplicating the work during the capture, but it also has its advantages. On the one hand we will use the same optics and sensor so that there is no disparity between the shots, on the other hand we can work with interaxial distances adapted to any scenario.
It is enough to make two captures, each one of them moving the entrance pupil to the right and left of the vertical nodal axis. This is the system called “Cha-Cha” by the traditional stereography.
All the captures proposed in the following chapter, can be made with a single camera.