Cardboarding
If objects look volumeless, like cardboard cutouts lined up one behind another, this is called cardboarding (cardboard effect). There is depth in the scene, but the objects themselves are flat.
Measured by roundness
The ratio of an object's perceived depth to its perceived width is called roundness. Near the screen plane:
where: b interaxial, V viewing distance, C convergence distance (object), e interocular distance
At ρ = 1 the object appears in its natural proportions; as ρ decreases it looks flattened. If ρ drops below 0.2, cardboarding becomes noticeable; this is a commonly used limit (Mendiburu).
Causes
- Small interaxial: depth is proportional to the interaxial.
- Shooting from a distance: ρ is inversely proportional to the convergence distance. This is why shooting a distant object with a long lens flattens the object. For example, with a 65 mm interaxial and a TV viewed from 2.5 m, ρ ≈ 0.71 if the object is at 3.5 m and ρ ≈ 0.13 if it is at 20 m.
- Viewing conditions: ρ is proportional to the viewing distance and independent of the screen width. If a film shot to be viewed from 16 m is viewed from 4 m, ρ is divided by four (Devernay and Beardsley).
What to do
Moving closer to the object or increasing the interaxial raises ρ; since both also enlarge the depth range, they are evaluated together with the comfort window. The calculator shows the roundness of the main subject in the result cards and in the checks.