3D TV essential guide Become a 3D TV expert

3D TV is growing apace with 3D-enable products - including 3D TV, 3D cameras and 3D camcorders - hitting the shops.

Which? is keeping on top of all things 3D to help you make the best decisions, and Which? reporters attended a 3D production discussion hosted by Buzz Hays, an executive stereoscopic 3D producer at Sony. Buzz Hays explained to us the complexities of shooting 3D films.

Interocular and interaxial distance

The interpupillary (also known as interocular) distance is the distance between our two eyes. It's because we have two eyes (binocular vision) that we are able to perceive depth. 3D camera rigs try to mimic this by using two lenses. The distance between the two lenses is the interaxial distance.

Cameras can be large devices so it's not always possible to place two side-by-side. When a 3D producer needs to use a small interaxial distance, they might use a beamsplitting, rather than side-by-side camera rig. A beamsplitting rig has one camera pointing at the action and another pointing upwards or downwards at a mirror that is beside the first camera.

3D producers can use different interaxial distances to play with the scale of subjects being filmed. Two cameras positioned far apart can reduce the scale of the object being filmed; This technique is called hyperstereo. Hypostereo is when the scale of an object is scaled down by using cameras positioned closer together.

Convergence control and 3D depth budget

Convergence control is another important control that 3D producers need to think about. If the two cameras are parallel then objects being filmed can appear two far away. To make the image appear in front of, or slightly behind the TV screen producers need to angle the cameras slightly towards each other. The point at which the two shots of the camera meet is called the convergence point.

When the convergence point is in front of the screen, it is called negative parallax. This make images seem to jump out of the screen. When the object appears to be behind the screen, it is called positive convergence. This makes watching 3D TV seem like you're looking through a window. A zero parallax describes an image that appears upon the screen.

The difference between the deepest and closest 3D effects used by a producer is called the depth budget. When Sky shoots football it uses a small depth budget as the choice of camera angle can't be pre-determined and a large depth budget can lead to players appearing in front of the on-screen titles that show the score. Furthermore, football might be watched on screens of small (pub and home) and large (cinema) sizes, and this is another key reason why the depth budget is limited. A 3D film for the cinema and Blu-ray will be 'massaged' to suit the different screen sizes.

Why is some 3D uncomfortable to watch?

In this clip, Buzz Hays talks about how the interaxial control and the convergence control have a practical effect on the way that 3D pictures are seen on TV. He talks about why some 3D footage can be uncomfortable, and why other material looks like cardboard cut outs.

He also looks at how the size of the screen that the 3D film is going to be watched on affects the production, and explains why 3D filmed for the TV, or for the cinema need to be approached in different ways.

Focal length and depth-of-field in 3D films

The focal length describes how much a lens is zoomed in or zoomed out. A wide-angle lens is one that can zoom out very far, and a very wide-angle lens (fisheye) can distort still images. The distorting effect on a 3D image is exaggerated when a very wide-angle lens is used.

Depth-of-field is a term that describes how much of the image is in focus. A shallow depth of field is often used in portrait photography as it can blur the background and give a pleasing effect. In 3D films, however, the producer will want the viewer to focus on certain parts of the image that are not always the closest (such as the object sticking out of the screen). In these instances, depth-of-field becomes a tricky technique to master.

Which? has rounded up the small number of 3D TVs that are currently available and has put them through their paces in our independent lab. As new 3D TVs launch we'll be updating our report, so you'll always know which 3D TV is the best.

For this detailed and unbiased information, check out our 3D TV reviews.