Stopping down your aperture is the easy way to get more of your scene in focus, but there's a point where it starts working against you. Here's why your images may not be as sharp as you'd thought
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The Smaller the Aperture, the Softer the Photo
Closing your aperture down brings more of the scene into focus. But go too far and the whole picture starts to lose its sharpness. This is diffraction.
A low f-number means a wide opening. Light passes through with almost no spreading, so a point in the scene lands on the sensor as a point and fine detail stays crisp.
The higher the f-number, the narrower the aperture. There is still plenty of detail at f/11 and it remains a perfectly usable setting, but light squeezing through the smaller gap has begun to spread. Diffraction is setting in and the finest details start to soften.
f/22 is about as small as most lenses go, so the spreading is at its worst. Every point is a soft blob, neighbouring details run into each other and the whole frame looks blurred.
That is the sweet spot for almost every lens, though it lands in a different place depending on where yours starts. Corners sharpen up about a stop after the centre, and smaller sensors reach their limit sooner. Only go past f/11 when you need the depth of field more than the last of the detail.
Want to keep this diffraction information handy?
Download a free PDF version of the diffraction infographic.
