Part 11 of 13 in the aperture guide
Does a smaller aperture always make a sharper picture?
Short answer. No. A very small opening bends light at its edge and softens the picture, and a very wide one shows lens flaws. Most lenses are sharpest a few stops below their widest, around the middle of their range.
- Diffraction: light spreads as it passes a small opening, so each point becomes a small disc. The disc is about 2.44 × wavelength × f-number wide.[3] For green light (0.55 micrometres) at f/16 that is about 21 micrometres, several times the width of a typical camera pixel, so the blur spreads over neighbouring pixels.[3]
- Wide open: lens flaws called aberrations are strongest at the widest openings.
- Sweet spot: most lenses are sharpest a few stops down from the widest opening, around the middle of their range.[2]
- Test your own lenses, because every lens is different.
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Questions people ask
Why are my photos soft at f/22?
At a very small opening light bends around the edges of the blades, which is called diffraction. It reduces fine detail.
Which aperture is sharpest?
Most lenses are sharpest a few stops down from the widest opening, around the middle of their range. Test your own lenses, because every lens is different.
References
- Wheeler, P. (2005) Practical Cinematography, 2nd edn. Oxford: Focal Press, pp. 101, 130, 139 to 140.
- Langford, M. and Bilissi, E. (2008) Langford’s Advanced Photography, 7th edn. Oxford: Focal Press, ch. 3, “Choosing lenses”, Fig. 3.19.
- Edmund Optics. Limitations on Resolution and Contrast: the Airy Disk. edmundoptics.com/knowledge-center/application-notes/imaging/limitations-on-resolution-and-contrast-the-airy-disk
All 13 questions in this guide
- What is aperture, and what does it do?
- What is a diaphragm, and how does it work?
- What is the difference between absolute and relative aperture?
- How is the f-number written, and why does a bigger number mean a smaller opening?
- Why does each f-stop multiply by 1.4 and not by 2?
- What are full, half and third stops of aperture?
- What is effective aperture?
- What is lens speed, and what does maximum aperture mean?
- How do I set the aperture on my camera?
- What is the difference between an f-stop and a T-stop?
- Does a smaller aperture always make a sharper picture?
- How does aperture affect depth of field?
- How do cinematographers use aperture?
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Creative Hut Academy in Mattakkara, Kottayam, Kerala teaches photography, cinematography, editing, sound and AI filmmaking in one-year residential diplomas. Students come from across India.
Guide by Abin Alex and Anu Joseph, Creative Hut Academy.