Why are f/8 to f/11 often considered the 'safe' apertures?
Asked 7/22/2013
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I often read that if you’re unsure which aperture to use, f/8 to f/11 is a good default. Why is that? My first thought was to use a much smaller aperture, like f/22 or f/32, to maximize depth of field and then add blur later in software if needed. Is f/8 to f/11 popular because it’s an optical sweet spot, or is it mainly just a compromise between sharpness, depth of field, and diffraction?
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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If you care about image quality then there isn't really a "don't care" aperture any more. With 35mm film the effects of diffraction at f/11 or f/16 weren't readily apparent, however with a high megapixel DSLR diffraction has a measurable effect at apertures as wide as f/5.6!
It's worth stating for the record: more megapixels does not make diffraction worse. But they do make it more apparent when quality is lower than it could be. If using a FF DSLR your images will be no worse than those taken at f/16 with a film SLR, but peak sharpness could be higher. That's why it makes a difference whether you really care about image quality or not.
If you don't care about image quality then use whatever aperture you feel like. The idea that if you have tons of light then you should stop down as far as possible to maximise DOF and cover focus errors and thus obtain the sharpest image is a misconception as you could potentially lose more sharpness over the critical parts of the image due to diffraction.
The only thing to do if you care about image quality is to care about the aperture setting and chose the appropriate value for each scene, taking into account your focal length, the distance the the subject, it's depth and the type of image you want to achieve. Good focusing technique is necessary too.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
13y ago
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f/8 to f/11 is often treated as a “safe” or “who cares” range because it’s usually a good compromise, not because it’s always best.
Why it works:
- Many lenses are very sharp when stopped down a bit from wide open, often around f/8 to f/11.
- You get more depth of field than at large apertures, which helps when the subject isn’t perfectly flat or focus placement isn’t critical.
- If you stop down too far, like f/22 or f/32, diffraction softens the image and can reduce sharpness.
So although smaller apertures increase depth of field, they do not automatically give the sharpest image. Past a certain point, the loss from diffraction outweighs the DOF benefit.
The “who cares” idea usually means the scene is flat enough, or all the important subjects are at similar distances, so exact DOF isn’t a major concern. In that case, using the lens near its optical sweet spot is a sensible default.
Bottom line: f/8 to f/11 is popular because it often balances lens sharpness, usable depth of field, and minimal diffraction. The exact best aperture depends on the lens, camera, and scene.
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