The Oculus DK2 is a remarkable VR headset, producing a remarkably wide field of view with very inexpensive single element optics. VRtifacts was curious about the characteristics of the Oculus DK2 lens: what size, what material, and what focal length? The lenses themselves have quite a bit of chromatic aberration, giving the impression that they are very low cost simple lenses. The diameter is 41mm and focal length (of the “B” lens) is approximately 45mm.
Distortion and Chromatic Aberration
This is a fairly high degree of magnification which produces significant distortion and chromatic aberration (color fringing near the lens periphery.) Oculus takes full advantage of modern day graphics cards using OpenGL to pre-distort opposite to the lens distortion, and to individually distort the red, green, and blue channels to (imperfectly) correct for chromatic aberration. The color fringing correction is imperfect because the lens bends different frequency light by different amounts. The process in the lens is a continuous curve across the color spectrum, while the graphics card only corrects at 3 discrete frequencies corresponding to red, green, and blue… essentially a step function. However, since the display emits moderately narrow bands red, green and blue, we perceive good chromatic aberration correction.
AMOLEDs (DK2 uses a Samsung Galaxy Note 3 Full HD Super AMOLED) use organic electroluminescent materials which do not emit single frequency red, green, and blue colors. Instead they emit a range of light frequencies consisting of a spectral curve for each color primary. AMOLED spectral curves are narrower than produced by IPS LCDs (used in Apple retina displays), but the width of the frequency range for each primary is not a single frequency. The Oculus chromatic aberration correction technique only works perfectly at the exact center frequencies of each (RGB) emission curve. Since the AMOLED emissions spread around these ideal Oculus corrected center frequencies, chromatic fringing can not be totally eliminated by the Oculus technique.
Spectrum plot for Apple iPhone 4 and 5 vs. Samsung AMOLED (older version than Note 3)