by Lin Yangchen
Optical system
Canon EOS-1D X
sensor: 35-mm-format complementary metal–oxide–semiconductor
18.1 million pixels at 6.95 µm pixel pitch for optimal resolution and signal:noise ratio
14-bit analogue–digital conversion
Distortion is practically non-existent in the MP-E 65 mm lens, as shown by a photograph of a pdf test grid.
lens: Canon MP-E 65 mm
undistorted rectilinear projection at very high magnification
ultra-low-dispersion lens element (neutralizes chromatic aberration)
indicated aperture set at f/5.6 (optimal tradeoff between spherical aberration and diffraction)
camera fitted with two-way spirit level
cable release with mirror lock-up (to minimize vibration)
ISO 100
digital sharpening off
digital enhancements off
The hi-fidelity optical system captures true detail with a larger dynamic range and greater colour depth than scanners and USB microscopes. The devices in the latter category often digitally interpolate lost colour and missing or blown-out detail to generate a sort of watercolour painting of the stamp with fake pixels liberally added to make it look big.
Manœuvring
Gitzo GT3541LS tripod (carbon fibre, rated load 18 kg)
Arca-Swiss Z1 ball head (rated load 60 kg)
heavy-duty, high-precision Kirk FR-2 screw-type focusing rail
Specimen mount
Edmund Optics fused silica disc (transmits ultraviolet-visible-infrared)
diameter 50 mm, thickness 4.00 ± 0.38 mm
transmitting surfaces parallel to within 5 arcmin, flatness 1λ at 632.8 nm
250–700 nm anti-reflection coating (R ≤ 0.015)
keeps stamp flat to ensure image planarity
Illumination
F&V HDV-Z96 light-emitting-diode panel (96 LEDs, 800 lux at 1 m, 5600 K)
Angle of attack approximately −30° to sharply delineate topographical features through shadows. NASA spacecraft use the same technique to map the moon, with the sun as light source. Scanners cannot do this.