Petrographic Thin Section Scanner Specifications

1. Scanning method and light path

• Tile based stitching rather than a single frame capture

• Transmitted light as standard, with switching between plane polarised and crossed polarised

• Reflected light as an option for opaque minerals, ore phases and polished sections

• Motorised XY stage moving the slide automatically during the scan

• Note: petrographic work needs both light paths, since transmitted only systems cannot show opaque minerals

2. Polarising system

• Polariser and analyser independently rotatable over 360 degrees with 0.5 degree accuracy or better

• Crossed polar extinction position calibratable against a known isotropic sample

• Support for gypsum and mica accessory plates for optic sign and interference order

• Stage or image rotation for extinction angle and cleavage angle measurement

• Note: without a rotatable analyser the extinction angle cannot be measured, losing key identification data

3. Objectives and resolution

• Common magnifications of 2X, 4X, 10X, 20X and 40X, with 4X and 10X most used in petrography

• Strain free objectives are mandatory to avoid false interference colours under crossed polars

• Working distance must clear thin section plus coverslip, especially above 40X

• Numerical aperture and resolution should be stated per magnification for structure and mineral work

• Note: ordinary objectives generate stress birefringence under crossed polars and distort identification

4. Stage and slide compatibility

• Standard thin sections of 46 by 26 mm with 0.03 mm thickness

• Stage travel covering the whole slide with repeatability of 1 micrometre or better

• Support for normal thin sections, impregnated sections and probe sections

• Adjustable slide clamping to avoid cracking or shifting the section

• Note: uneven section thickness causes focus drift across one slide, so flatness should be checked first

5. Stitching accuracy and image quality

• Stitching repositioning error within one pixel or one micrometre

• No visible brightness bands at seams, requiring flat field correction and intensity balancing

• Colour reproduction matching visual observation, since interference colour is identification data

• Z axis autofocus tracking to handle uneven section thickness

• Note: interference colours are measurements rather than decoration, so camera colour management must be calibratable

6. Scanning speed and throughput

• One thin section at 10X within 5 minutes including autofocus and stitching

• 60 to 100 sections per eight hour shift depending on magnification and area

• Batch loading with multi slide magazines and optional automatic feeder

• Live preview during scanning with pause and resume

• Note: throughput figures must state magnification and section area to be comparable

7. Image analysis and quantification

• Grain size statistics including equivalent diameter, aspect ratio, area fraction and size distribution

• Mineral phase area percentage by colour, grey threshold or machine learning classification

• Porosity, fracture density, grain contact and cement type analysis

• Export of raw images with annotation layers for verification

• Note: colour based mineral identification must state accuracy, since 90 and 70 percent are very different

8. Software and data management

• TIFF, JPEG and pyramidal formats with multi level zoom viewing

• Raw data volume per section stated, typically 1 to 5 gigabytes at 10X over a full slide

• Local network multi client viewing with access control

• Database search by sample number, borehole number and depth

• Note: geological samples are archived by borehole and depth, so systems without search are just image piles

9. Where procurement goes wrong

• Transmitted light only, leaving opaque and ore minerals completely unobservable

• Objectives that are not strain free, producing false interference colours that distort results

• Stitching without flat field and intensity balancing, so seams remain and area statistics shift