Technical Details and notes - Equations for pre capture

Here are some equations and notes I've taken that I'll have to properly familiarise myself with by the time my 3D rig is ready.

Stereoscopic Parallax Budget (sometimes called Depth Budget) vs Depth Bracket

The Depth Bracket of your scene refers to the actual distance between your closest object in the frame and the furthest object.  The Parallax Budget refers to your calculated maximum positive parallax and desired maximum negative parallax represented in percentage of screen width.  For example if I determine through a simple calculation that my positive parallax should never exceed 0.7% of screen width and I have determined that my negative parallax should not exceed 2% of screen width, then my total Parallax Budget is 2.7%.   The Depth Bracket must be able to be squeezed into the Parallax Budget.  There are many algebraic formulas to determine the proper interaxial distance to achieve this.

Native Parallax for final display size

The native parallax for a given screen size simply refers to what percentage of screen width will equal the human interocular.  If you are using 2.5 inches as the baseline interocular and you know your presentation screen will be 30 feet wide (360 inches) then just divide 2.5 by 360.  2.5 ÷ 360 = 0.007 or 0.7%  Therefore the Native Parallax of a 30 foot screen is 0.7%, so we should make sure to keep our maximum positive parallax under 0.7% of screen width if we plan to show our footage on a 30 foot wide screen.  If we shoot for a 65” 3DTV, then we can get away with over 3% positive parallax.

The 1/30th Rule

The 1/30 rule refers to a commonly accepted rule that has been used for decades by hobbyist stereographers around the world.  It basically states that the interaxial separation should only be 1/30th of the distance from your camera to the closest subject.  In the case of ortho-stereoscopic shooting that would mean your cameras should only be 2.5” apart and your closest subject should never be any closer than 75 inches (about 6 feet) away.

Interaxial x 30 = minimum object distance

or

Minimum object distance ÷ 30 = Interaxial

If you are using a couple standard 6″ wide camcorders in a side by side rig as close as they will fit together then the calculation would look like: 6” x 30 = 180 inches or 15 feet.  That’s right… 15 feet!

But does the 1/30 rule apply to all scenarios?  No, the 1/30 rule certainly does not apply to all scenarios.  In fact, in feature film production destined for the big screen we will typically use a ratio of 1/60, 1/100 or higher.  The 1/30 rule works well if your final display screen size is less than 65 inches wide, your cameras were parallel to each other, and your shots were all taken outside with the background at infinity.  When you are ready to take the next step to becoming a stereographer you will need to learn about parallax range and the various equations available to calculate maximum positive parallax (the parallax of the furthest object,) which will translate into a real-world distance when you eventually display your footage.

Remember that illustration on page 3 of the eyes pointing outward (diverging)?  Well it isn’t natural for humans to diverge and therefore the maximum positive parallax when displayed should not exceed the human interocular of 2.5 inches (65mm).   You can readjust the convergence point and bring the maximum positive parallax within the limits of the native display parallax (2.5 inches) but that will also increase your negative parallax.

3D photography tests + Active Shutter & Passive Display techniques

So I couldn't wait to get started and make some 3D images. I decided to jump right in and do a bit of hands-on research even though I'm yet to build my rig, or source 2 identical cameras to shoot with.

The basics I operated from:
- A stereoscopic image is composed of two images of the same scene, captured with a small distance in position along the same axis.
- All the settings must be the same (Focus, exposure, shutter speed, etc)

I only had one camera available at this stage so there were some other things I had to operate by:
- The scene had to remain unchanged
- At this early stage of stereoscopic learning, the camera angle (or convergence) should stay the same.

So here is how I did it:

I didn't have a dolly on hand so I found a flannel and slid it to the left on the second capture.

I edited the two photos together in Photoshop and saved it as the JPS file format.

Blogger doesn't allow embedding of JPS files, but this is what it looks like as a side-by-side stereoscopic file.

I have a 3D monitor wnd NVIDIA 3D Vision glasses, so this shows the left eye...

And the right one.

This is just a video demonstration of the above images.

So this 'no-budget' test was very successful. This was also the second attempt. On the first go round I did not take proper care to keep the camera aligned, so the 3D effect was thrown off.

If you have a means of viewing 3D images here is the file for you to download and see for yourself: This is the link.

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Stereoscopic 3D display Technologies

The display technique shown here to display my work is using active shutter technology. For this to work, the screen has a refresh rate of 120hz and the glasses sync with this, blocking the lenses asynchronously so that the left eye sees the left image and the right eye sees the right image one after the other. This happens so fast that we (usually) don't notice any flicker or ghosting.

An alternative display technique to this (and one that most cinemas employ for their 3D projection) is passive 3D which makes use of horizontally and vertically polarized lenses. The images are projected with matching polarisations onto the same screen or surface at the same time, with each eye seeing the intended image through the polarised filters on the lenses of the glasses.

Some general information about 3D capture.

There are terms in this post that you may not understand. Please refer to this page for any definitions you may be unsure of: http://jamesgodfrey3dstudy.blogspot.co.nz/2015/12/some-key-terms-and-phrases.html

Ortho, Hypo, and Hyper stereoscopy

With the interocular distance being about 65mm on average for an adult, most stereographers use this as a stereo-base. When the the interocular and interaxial distances are the same, then you are shooting in ‘Ortho-stereo’.

If the interaxial distance used in smaller that this you then shoot in ‘Hypo-stereo’. This technique is common for theatrically released films to accommodate the effects of the big screen.  It is also used for macro stereoscopic photography.

Lastly ‘Hyper-stereo’ refers to interaxial distances greater than 65mm. The greater the I.O. the greater the depth. The only potential issue with this is that gigantic real life objects may appear as if they were small models.

Decreasing the interaxial separation between two cameras to 30(ish)mm or less will allow you to shoot amazing macro stereo-photos and separating the cameras to a meter or so apart will allow great depth on mountain ranges, city skylines and other vistas.

Some notes on side-by-side stereoscopic 3d capture

Here are some notes that I've taken thus far in regards to side-by-side stereoscopic 3D capture.

BOLD for importance.

Side-by-Side does not allow for close-ups - beam splitters (over-under) do allow this as the camera lenses can converge.

Never use ‘Auto-anything’ to capture stereographic footage! Turn Image Stabilisation off. Manually set the white balance. Set the focus by hand.

It is recommended to shoot with progressive formats whenever possible - not interlaced.

In shooting with a two camera setup in may be beneficial to use two cameras that can be ‘genlocked’ together. Cameras that cannot be genlocked will have some degree of temporal disparity.

Slow down your pans - However fast you are used to panning in 2D, cut the speed in half for 3D.

Useful sites, links, and videos regarding stereoscopic 3D capture

Very Useful site:

http://www.dashwood3d.com/blog/beginners-guide-to-shooting-stereoscopic-3d/

Description: A very easy to understand beginners guide to stereoscopic 3D capture.

Stereoscopic Multiplexer driver for live 3d (windows only)

http://www.3dtv.at/Products/Multiplexer/Index_en.aspx

Description: a windows only tool (which is possibly now out of date) that I came across. I am yet to properly look into it, but it looks like it allows for a live-feed of your 3D capture setup, so you can check your shots before shouting action.

3D Rig info

http://realvision.ae/Location_Previz_3D.pdf

Description: A very useful pdf detailing one company's on-location pre-visualisation for 3D video.

3D Steadicam demo

https://www.youtube.com/watch?v=hSnyfREP6Nc

Description: A video demonstration of a 3D camera rig mounted on a steadicam setup. This is more for interests sake, and you'll learn things more by osmosis watching him than by being specifically taught anything.

James Cameron Talks about his 3D camera rig

https://www.youtube.com/watch?v=142gTbBDzWM
Description: A very interesting video in which James Cameron talks about the benefits of his custom stereoscopic rig, and shooting over-under, compared to side-by-side - among other things.

Side-by-side rig demo

https://www.youtube.com/watch?v=gJlkuHxQB20

Description: A demonstration of a side-by-side camera rig. From this I gleaned some useful information about rig construction as well as some features I want to add, that this one is missing.

Multiple camera recording via usb

http://www.breezesys.com/MultiCamera/index.htm

Description: A piece of software that controls multiple camera from one PC. An option for filming with my yet-to-be-made 3D rig as it theoretically will start recording at the same time on both cameras.

Multiple camera recording via infrared remote
http://www.pbtech.co.nz/index.php?z=p&p=CAACNP9006I

Description: A possible solution for the "needing to start the recording at the same time' problem. It is a link to an infrared remote for Canon DSLR cameras.

Some Key Terms and phrases

This post contains a list of stereoscopic 3D related terms and phrases. Most of these are standard industry terms. It serves as a kind of topic specific glossary/dictionary. Words have been added to this based on my current knowledge - i.e. if I didn't know what it meant I made a note of it and found out. There are also a few core stereoscopic terms that I already knew about that are on this list, but I figured the information may be useful for others who come across this list. (I'll also be regularly updating this list throughout my research project, and make a separate post linking here each time I update it.)

Interocular

The interocular separation (or interpupillary distance) refers to the distance between the centers of the human eyes.  For a male adult this distance is typically accepted to be an average of 65mm (roughly 2.5 inches).

Interaxial

Interaxial separation is the distance between the centers of two camera lenses. The human interocular separation is an important constant stereographers use to make calculations for interaxial separation.

Interaxial separation is often incorrectly referred to as “Interocular” and vise-versa. Interaxial separation has come to be known as “i.o.” even though it is the incorrect term.

Convergence

How cross-eyed your eyes are, and how angled the cameras should be to mimic this.

JPS

A stereographic image format based on JPEG. It stands for JPEG Stereoscopic.

Negative Parallax (before the window)

An object appears as if it is close to you; between you and the window.

Zero Parallax

An object is situated on ‘the window’ or ‘screen plane’.

Positive Parallax (behind the window)

An object appears as if it is far away from you; behind the window.

Window Violation

A window violation occurs when an object appears to be before the window, but is touching the edge of the screen. The brain is unable to understand this parallax as it is suggesting the object is before the screen, but at the same time it is obstructed by the screen edge - this will often cause great viewer discomfort.

Stereo-base

See Interaxial
Disparity

Vertical, rotational, zoom, keystone or temporal differences between the left and right eye images. A stereographer never wants disparity, as this can break the 3D effect and cause muscular pain in the viewer’s eyes or even nausea.

Genlock

A device for maintaining synchronization between two different video signals, or between a video signal and a computer or audio signal, enabling video images and computer graphics to be mixed.

Introduction

Welcome. This blog will chronicle my research journey into 3D stereoscopic film and photography. It will contain my research into everything from the history of stereoscopic cinema, the foundations of stereoscopic image capture, recommended techniques and tips for subject selection and capture, examples and 3D case studies and will also chronicle the process I take in creating my own personalised stereoscopic 3D DSLR camera rig.