How is the acceptable circle of confusion chosen for depth-of-field calculations?
Asked 2/5/2013
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Different depth-of-field calculators use different circle of confusion (CoC) values for the same sensor sizes, which changes the reported DOF and hyperfocal distance. How is an acceptable CoC actually determined? Does it depend on final display size and viewing distance, and if so, how would you estimate a suitable CoC for a particular print or screen image?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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The acceptable CoC depends on the point at which increases in resolution yield only a marginal increase is perceived detail. This in turn depends on your eyesight, distance from the media and properties of the media in question.
You can either determine this value yourself, or accept a figure that Zeiss (supposedly) came up with decades ago and divide the diagonal of your print size by 1730. Most do the latter.
One final note, the acceptable CoC for web sized shots is huge, so much so it renders DoF calculations almost redundant.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
13y ago
0
Generated from our catalog & community — verify before relying on it.
The “acceptable” circle of confusion is not a fixed property of the camera. It’s an output/display assumption used to decide how much blur still looks sharp enough.
In practice, CoC depends on:
- viewing distance
- final display or print size
- viewer eyesight
- how critical you want “sharp” to be
That’s why different DOF calculators give different results for the same sensor size: they’re using different assumptions.
A common traditional rule is to base CoC on the image or format diagonal, using roughly:
- diagonal / 1730, or
- diagonal / 1500
These are only conventions, not physical laws. They come from old assumptions about a “standard” print size and viewing distance (often around an 8×10 inch print viewed from about 10 inches).
So yes: if you make a larger print from the same image, or view it more closely, the acceptable CoC should be smaller. If the image is shown small on the web or viewed from farther away, the acceptable CoC can be much larger, making DOF effectively more forgiving.
Bottom line: CoC is an arbitrary but useful approximation. Choose a stricter value for large prints/close viewing, and a looser value for small web display or distant viewing.
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UniqueBot
AI13y ago
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