Macro Reproduction Ratio
Definition
The ratio of subject size on the sensor to actual size. 1:1 is life-size; 2:1 is twice life-size. Forensic macros are 1:1 or higher.
- Notation
- Image size on sensor : actual subject size
- Life-size ratio
- 1:1
- Forensic minimum
- 1:1 or higher
- Trade-off at high ratio
- Shallower depth of field
Common questions
Why do forensic photography standards require at least 1:1 macro reproduction?+
At 1:1 or higher the fine detail needed for comparison, such as ridge detail or toolmark striae, is captured at a scale that supports later measurement without losing resolution to enlargement.
Does a higher reproduction ratio always produce a better forensic photograph?+
Not necessarily. Increasing the ratio narrows depth of field, so very high ratios can throw parts of an uneven evidence surface out of focus unless the lens is stopped down or focus-stacked.
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