The book scanner needs a camera lens with a flat focus field. Most affordable lenses are spherical field. I’m evaluating the Raspberry Pi HQ camera, which has 12 megapixels (sufficient for A4 at 300 dpi) and has variants taking C/CS mount or M12 mount lenses. C/CS is the old 16mm cine format, since adopted for CCTVs, so there’s a long history of lenses. Camera specs:
Sensor
: Sony IMX477R stacked, back-illuminated sensor, 12.3 megapixels, 7.9 mm sensor diagonal, 1.55 μm × 1.55 μm pixel size
Output
: RAW12/10/8
Back focus length of lens
: 2.6mm–11.8mm (M12 Mount variant), 12.5mm–22.4mm (CS Mount variant)
Lens sensor format
: 1/2.3” (7.9mm) or larger
IR cut filter
: Integrated
Ribbon cable length
: 200 mm
Tripod mount
: 1/4”-20
As per Arducam, sensor inch sizes aren’t actual inches but just a naming convention:
Focal length calculator for a 13” field of view from same distance away:
Catalogues
Tamron
Arducam
Easily available, but Arducam doesn’t specify if they are flat focus, so this needs verification. Maybe that is what they mean by “low distortion”? (Nope, that refers to barrel and pincushion distortion.) Full list.
I wrote to Arducam and they recommended the LN024, without clarifying if it has flat-field focus. It doesn’t have a focus ring, so I assume it’s infinity-focus.
Candidates
| Brand | Model | Mount | Sensor | FL | FoV | USD | INR |
|---|---|---|---|---|---|---|---|
| Tamron | M118VM413IR | C | 1/1.8” | 4.0–13mm | 105.4°×77.6° | $285 | |
| Tamron | M118VG413IR | C | 1/2” | 4.0–13mm | 91.7°×67.9° | $240 | |
| Arducam | LN051/CS17320M12 | CS | 1/1.7” | 3.2mm | 120° H | $30 | ₹2739 |
| Arducam | LN024/M2306ZM13 | M12 | 1/2.3” | 6mm | 50° H | $13 | ₹1027 |
| Arducam | LN064/M23325H12 | M12 | 1/2.3” | 3.25mm | 120°×83° | $20 | ₹2149 |