by John Wattie (kiwizone) This version: March 19, 2012
Panasonic Meduza Fuji
The idea of moving the camera receptor sideways for convergence control, adjusted by a linear motor, was mentioned on the previous page. There is no reason to use mechanical receptor motion if it can be replaced by electronic control for:
Variation in stereo base has to be mechanical, (albeit motorised) since it involves moving the the two cameras sideways, but the remaining stereo geometry control is electronic.
Oversize receptors in the two cameras are set up parallel, so there is no keystone distortion at any stage.
A large 2K or even 4K CCD chip is suggested, but only part of the CCD is used for the image. This portion might be:
1/30 rule for stereo base would be 1920/30 = 65 pixels needed for convergence.
Convergence is done by electronically moving the smaller portion of the CCD used for imaging (instead of moving the whole sensor mechanically).
It is even possible with an oversize chip to move the two image reception zones vertically, to overcome converging verticals, without the need for shift lenses.
The alignment corrections could be viewed in real time during filming, in stereo if desired.
Big sensors means many pixels, times 2 because we are outputting stereo means a big big computer needed, hopefully without hitting the "2K limit." (2048x2048).
The advantages are:
This is the same as the old Stereo Realist film camera. (Asymmetrical frustrum with no keystone distortion).
Improvements possible are:
Looking at this picture of the prototype Panasonic 3D movie camera I cannot see any correction for stereo base. That is not good, because I use base adjustments extensively. A small stereo base will not do for sports 3D TV.
A new camera (2011) which does have variable stereo base and convergence, interchangeable lenses and even interchangeable 4K sensors. It can be controlled from an iPad or Android: Utube
Silicon Imaging SI-2K is said to have digital convergence because it outputs direct to a Windows computer running post processing software. But buy two of those for 3D and you are into big bucks.
There are rumours the Panasonic Full HD 3D camcorder, which is not yet available on the market, will be using the digital convergence and alignment system described here.
This is the first digital stereo camera on the market.
Victor Reijs has done experiments on the Fuji camera and found parallax variation was more complex than initially suspected.
So the Fuji camera is converging using two methods at once.
In the camera's automatic mode, the stereo window is placed at the focussed distance (like the Loreo beam splitter does). Since the optical convergence angle is fixed, the variable convergence must be done by HIT on the sensors.
Convergence can also be done manually. However, it seems this only works on the 3D viewer on the back of the camera, but that is great for checking the stereo image when big convergence close-ups are taken. Convergence needs to be done again in post-processing, which is no problem with Stereo Photo Maker program.
Having the object of interest in sharp focus and also at the convergence point is a method favoured in movies, including Avatar.
The advantage is the object of interest is on the screen surface, meaning no stereoscopic disparity, which is easy on the eyes, especially for an audience which is not trained in stereoscopic viewing. No conflict occurs between focus and convergence in the eyes of the audience.
Convergence and focus are linked, making it easier to vary them both simultaneously and keep a moving actor at zero disparity
The object of interest has no disparity ghosting.
The director can draw attention to the main feature by having it in focus, on the screen and ghost-free, even if it is moving
Convergence on the focus point causes a window violation, unless floating windows are used, or if it is considered acceptable to have objects overlapping the lower edge of the screen.
The animated 3D movie, Toy Story 3, does use floating windows but at times also overlaps the lower screen edge to project objects into the movie theatre space. But the projected object is usually dark, and so merges into the dark of the theatre and it takes an astute observer to realise what has happened.
Overlap of the upper screen edge is not acceptable, since we do not enjoy having a character's head split by the screen.
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Jay Gharavi: 20/4/10
The hardware design and picture processing pipeline of the digital camera style sensors, including those with video capture capability, assumes that the entire effective area of the sensor yields a single frame per capture. This means that it may not be feasible to force the system to capture a frame mapped only from a part of the sensor, in real time. The implication is that the desired mapped frame may have to be extracted from a fully captured frame.
Another point that worries me a little, is the offset axis of the lens(though the offset may not be large enough to cause trouble). Lenses with large image circles are necessarily more bulky, and complicated, adversely affecting the design choices (zoom range, max aperture, minimum focus, etc.), bringing to question their usefulness as the normal lens.
Over-sized sensor means over-sized lens distortions which makes toe-in a superior method since only barbell and keystone correction is required.
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I'm not sure I got the whole idea, because for HDTV cameras now a 36mm senzor is oversized, but for 36 a 6x6 etc... but here is something as a quick over:
Well, there are some nice points here. But custom sensors are expensive :-)
Nice one and keep going!
"If the cameras are thin (such as the 65mm SI-2K Mini) there is no need for a mirror box because the stereo base (I.O.) can be set at the normal 65mm."
Oversize!? The chips are 1/4", this is not enough to qualify as HD for ANY channel (Sky, nat Geo, Discovery), even if you use all of the chip. If there is extra room on a 1/4" chip then how much is left? Now, the EX3D camera (with 1/2" chips and HDSDI out at 10 bit off the sensor) is a much more interesting proposition - particularly, as I hear, it will use interchangeable C mount lenses and thus be able to get a min i/o of 1.5" as opposed to the 2.5" of the Panasonic
I'd say that electronic transformation of picture information captured by camera sensor could be thoughtfully done in post, or TV station. The more functions are built into the camera, the less interactive control you have, the more consumer (vs. professional) the camera appears.
Parrallel camera's with digital post processing works fine with the added benefit that its extremely easy to align the rigs with a checkerboard.
Introduction to Mounting cameras for stereo
Practical and theoretical stereo rigs ( more details than given on this page )