How to use it
- Pick metric or US units and the sensor size of your camera.
- Enter the focal length in millimetres, the f-number and the distance to your subject.
- Read where sharpness begins and ends, and the hyperfocal distance for those settings.
How it works
All distances are worked in millimetres with the standard formulas, where f is the focal length, N the f-number, c the circle of confusion and s the focus distance:
- Hyperfocal distance: H = f² ÷ (N × c) + f
- Near limit: s × (H − f) ÷ (H + s − 2f)
- Far limit: s × (H − f) ÷ (H − s), or infinity once s reaches H
The circle of confusion c is the largest blur spot that still looks like a point. The calculator uses 0.030 mm for full frame, 0.020 mm for APS-C and 0.015 mm for Micro Four Thirds. These are conventional values; viewing size and eyesight change what looks sharp.
Worked example
A 50 mm lens at f/2.8 on a full-frame camera, focused at 3 m. H = 50² ÷ (2.8 × 0.03) + 50 = 29.8 m. The near limit is about 2.73 m and the far limit about 3.33 m, so roughly 0.6 m of the scene looks sharp.
Tips
- For a landscape, focus at the hyperfocal distance: everything from half that distance to infinity is acceptably sharp.
- Depth of field is shallower at wide apertures, long focal lengths and close focus.
- The limits are an estimate. If a print will be viewed very closely, stop down a little further than the numbers suggest.