Depth of Field (DoF)
Definition
The zone of acceptably sharp focus around the focused plane; controlled by aperture, focal length, and subject distance. Critical for close-up evidence photography.
- Controlled by
- Aperture, focal length, subject distance
- Narrower aperture
- Greater depth of field
- Relevance
- Close-up and macro evidence photography
- Tradeoff
- Smaller aperture needs more light or longer exposure
Common questions
Why is depth of field especially critical in close-up evidence photography?+
At macro distances the zone of sharp focus becomes very shallow, so a mark, tool impression, or fingerprint can easily have part of its surface out of focus. Photographers use a smaller aperture and, where needed, a tripod and slower shutter speed to keep the whole item of evidence sharp.
Does a wider aperture ever help evidence photography?+
Yes, when the goal is to isolate a subject from a cluttered or distracting background, a shallow depth of field from a wider aperture can be used deliberately, though this is less common in documentation shots where the whole item must stay in focus.
Related terms
- ABFO No. 2 Scale
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- CCD (Charge-Coupled Device)
- A sensor architecture that transfers accumulated pixel charge across the array to a single output amplifier, producing uniform noise characteristics suitable for...
- CMOS (Complementary Metal-Oxide Semiconductor)
- A sensor architecture with per-pixel amplifiers, enabling fast readout and low power consumption; BSI-CMOS variants now dominate professional forensic cameras.
- Diffraction Limit
- The aperture threshold below which wave diffraction at the aperture edges degrades resolution more than the narrower aperture improves depth of field....
- Dynamic Range
- The ratio in exposure stops between the brightest recordable highlight and the darkest shadow detail above the noise floor; typically 12-14 stops...
- F-Stop
- The ratio of focal length to aperture diameter, expressed as f/number. Lower numbers mean wider aperture, more light, and shallower depth of...
- Focus Stacking
- A computational technique combining multiple images focused at sequential depths into a single all-in-focus image; used for three-dimensional evidence with relief exceeding...
- ISO
- A standardised sensitivity rating for digital sensors; higher ISO values amplify the output and allow lower-light capture but introduce random noise that...
- Oblique Lighting
- A lighting geometry with the source at 5-30 degrees to the evidence surface, casting long shadows that reveal surface relief. Standard for...
- Ring Flash
- A circular flash tube mounted around the lens that illuminates from all azimuths simultaneously, producing uniform shadowless illumination used for bite-mark and...
- White Balance
- A camera setting that corrects for the colour temperature of the ambient illuminant, ensuring neutral colours render as neutral. Manual white balance...