Optics & Physics Tutorial
Understanding Depth of Field & Hyperfocal Distance
Depth of field (DoF) is the zone of acceptable sharpness within an image that will appear in sharp focus from front to back. Mastering DoF lets you selectively isolate portraits with velvety bokeh or render expansive mountain landscapes sharp from foreground wildflowers to distant horizon peaks.
| Sensor Format | Sensor Dimensions | Crop Factor | Circle of Confusion (CoC) | Equivalent 50mm f/1.8 DoF (at 3m) |
|---|---|---|---|---|
| Full Frame 35mm | 36.0 × 24.0 mm | 1.0x (Reference) | 0.030 mm | 31.5 cm (Shallow Bokeh) |
| APS-C (Sony, Nikon, Fuji) | 23.5 × 15.6 mm | 1.5x | 0.020 mm | 47.2 cm (Moderate Bokeh) |
| APS-C (Canon) | 22.3 × 14.9 mm | 1.6x | 0.019 mm | 50.4 cm |
| Micro Four Thirds (MFT) | 17.3 × 13.0 mm | 2.0x | 0.015 mm | 63.1 cm (Deeper Focus) |
| Medium Format (44×33) | 43.8 × 32.9 mm | 0.79x | 0.038 mm | 24.8 cm (Ultra-Thin Focus) |
What is Hyperfocal Distance and how do I use it?
Hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. When you focus your lens precisely at the hyperfocal distance, your depth of field extends from half the hyperfocal distance all the way to infinity. This is the cornerstone technique for landscape and astrophotography!
Why do smartphones have so much deeper depth of field than DSLRs?
Smartphones use physically tiny image sensors (~1/1.3-inch or smaller). To achieve a standard wide field of view, smartphones use actual focal lengths around 6mm to 9mm. Because depth of field increases exponentially as focal length decreases, small smartphone sensors produce massive depth of field even at fast apertures like f/1.8.
Does aperture alone control background blur (bokeh)?
No! Depth of field is controlled by three factors working in harmony: physical focal length, f-stop aperture, and camera-to-subject distance. Subject distance is the most powerful variable: moving twice as close to your subject reduces depth of field by a factor of four!