Microscope Magnification Selection Guide
Guide to selecting appropriate magnifications for different metallographic applications and analyses.
Download PDF Guide
Get a printable guide with recommended magnification ranges for common metallographic applications.
Recommended Magnification Ranges
Overall sample overview
Magnification: 10x - 50x
Low magnification for viewing entire sample, checking for cracks, large defects, or overall structure.
Use case: Initial inspection, sample orientation, large-scale features
Grain size determination
Magnification: 100x - 500x
Standard range for grain size measurements using comparison charts or intercept methods (ASTM E112).
Use case: Grain size analysis, ASTM E112 compliance, quality control
Phase identification
Magnification: 200x - 1000x
Medium to high magnification for identifying different phases, constituents, and microstructural features.
Use case: Ferrite/pearlite, martensite, bainite identification, phase analysis
Inclusion rating
Magnification: 100x - 500x
Standard magnification range for inclusion content analysis and rating according to ASTM E45.
Use case: Inclusion analysis, ASTM E45 compliance, cleanliness assessment
Carbide analysis
Magnification: 500x - 1000x
Higher magnification needed to resolve fine carbides and second-phase particles in tool steels and high-alloy materials.
Use case: Tool steel analysis, carbide distribution, precipitation studies
Precipitation analysis
Magnification: 500x - 2000x
High magnification for observing fine precipitates, GP zones, and age-hardening features.
Use case: Aluminum alloys, precipitation-hardened materials, age-hardening studies
Surface finish evaluation
Magnification: 50x - 200x
Moderate magnification for evaluating surface quality, scratches, polishing artifacts, and preparation quality.
Use case: Quality control, preparation assessment, artifact identification
Coating thickness measurement
Magnification: 200x - 1000x
Magnification range for measuring coating thickness, case depth, and surface treatment layers.
Use case: Coating analysis, case depth measurement, surface treatment evaluation
Weld microstructure
Magnification: 50x - 500x
Range for examining weld zones, heat-affected zones, and fusion boundaries in welded materials.
Use case: Weld analysis, HAZ examination, fusion zone characterization
Failure analysis
Magnification: 50x - 2000x
Variable magnification depending on feature size - from crack propagation paths to fine fracture features.
Use case: Crack analysis, fracture surface examination, failure investigation
Intermetallic phases
Magnification: 500x - 2000x
High magnification required to resolve fine intermetallic phases and compounds in complex alloys.
Use case: Superalloys, titanium alloys, complex phase structures
Twin boundaries
Magnification: 200x - 1000x
Moderate to high magnification for observing annealing twins, deformation twins, and twin boundaries.
Use case: Austenitic stainless steel, copper alloys, twinning analysis
General Guidelines
Start low, go high
Always begin examination at low magnification to get overall context, then increase magnification to examine specific features of interest.
Use appropriate magnification for feature size
Select magnification so that the feature of interest occupies a reasonable portion of the field of view (typically 20-80% of field).
Consider resolution limits
Optical microscopes have resolution limits (~0.2 μm). Features smaller than this cannot be resolved regardless of magnification.
Balance magnification and field of view
Higher magnification provides more detail but reduces field of view. Choose based on whether you need detail or context.
Use standardized magnifications for comparisons
When comparing samples, use the same magnification for all images to ensure fair comparison and accurate documentation.
Calibrate regularly
Regularly calibrate microscope magnification using stage micrometers to ensure accurate measurements (ASTM E1951).
Important Notes
- Magnification values are approximate and may vary based on specific microscope and objective lens combinations.
- Total magnification = Objective magnification × Eyepiece magnification (typically 10x).
- Digital magnification on camera systems may differ from optical magnification - always calibrate.
- Resolution is limited by wavelength of light (~0.2 μm for visible light). Higher magnification does not improve resolution beyond this limit.
- For quantitative measurements, always calibrate using stage micrometers (ASTM E1951).
- Consider depth of field: higher magnification reduces depth of field, making focusing more critical.
- Use appropriate lighting (brightfield, darkfield, DIC, polarized) based on feature contrast needs.
Need More Help?
Check out our guides on microstructural analysis and equipment overview.