Plenoptic Camera Design
Plenoptic (light-field) camera design: lenslets and views, microlens f-number matching, refocusable object range, data size and assembly tolerance (Ng 2005).
Spatial samples (lenslets)
288 × 288
one sample per 125 µm lenslet
Views N × N
13 × 13 = 169
whole pixels across a micro-image; 61.87 arcmin per pixel at the lenslet
Microlens vs main-lens f-number
f/4.00 vs f/4.00
micro-image 100 % of the pitch: matched: micro-images tile the sensor
Refocusable object range
809 mm – 1.34 m
image side ±N·N_w·p_µ = ±6.50 mm; conventional ±0.500 mm
4D light field
14.02 M samples
28.04 MB at 16 bit; raw frame 32.00 MB
Lenslet-to-sensor tolerance
±36.0 µm
p_px·f_µ/p_µ; lenslet Airy diameter 5.37 µm vs 9.0 µm pixels
Model
A plenoptic camera (Ng et al. 2005) puts a microlens array where the sensor would be and the sensor one microlens focal length f_µ behind it. Each lenslet is one spatial sample, and the N pixels across its micro-image sample the main-lens aperture: N × N views of the scene. The defaults are close to Ng's prototype (125 µm f/4 lenslets, 9 µm pixels), whose micro-images are 12 pixels across (§6.3).
The micro-image of the aperture has diameter f_µ/N_w, so the microlens f-number f_µ/p_µ must equal the main lens's image-side (working) f-number N_w. A larger N_w leaves unused pixels; a smaller one makes neighbouring micro-images overlap, mixing neighbouring views in a band D − p_µ wide, so N counts only the 2p_µ − D clean pixels. The lenslet-to-sensor spacing must be right within p_px·f_µ/p_µ.
Refocusing sums shifted sub-aperture views, each seen through an aperture N times narrower, so a refocused image is sharp (blur within one lenslet) over the depth of field of an f/(N·N_w) lens: ±N·N_w·p_µ on the image side, mapped to object distances by the thin-lens equation. Ng's prototype refocused within the depth of field of f/22 against the ideal f/45, about half this (§6.3).
Spatial–angular trade-off (matched lenslets)
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
Plenoptic 1.0 with the sensor one microlens focal length behind the array. Refocus range: geometric depth of field of an f/(N·N_w) aperture with the lenslet as circle of confusion, through a thin main lens; Ng's prototype reached about half of it. Overlapping micro-images keep only 2p_µ − D clean pixels.
- Ng R., Levoy M., Brédif M., Duval G., Horowitz M., Hanrahan P. (2005). Light field photography with a hand-held plenoptic camera. Stanford Tech. Rep. CTSR 2005-02. Sections 3.1, 3.2 and 4.2. graphics.stanford.edu
- Levoy M., Ng R., Adams A., Footer M., Horowitz M. (2006). Light field microscopy. ACM Trans. Graph. 25(3), 924–934. Eqs. 1–5 and Table 1. doi:10.1145/1141911.1141976