Softness is exaggerated for illustrative purposes to show the concept and effects of diffraction.
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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What is Lens Diffraction?
The Smaller the Aperture, the Softer the Photo
Stopping down your aperture (f-stop or f-number) brings more of the scene into focus. But go too far, and the whole picture starts to lose its sharpness. This is known as lens diffraction. See the f-stops below for their relative sharpness with regard to diffraction.
f/2.8 – f/5.6
Sharpness
Image very sharp, fine detail
Low f-number, wide aperture
A low f-number means a wide opening on your lens. Light passes through with almost no spreading, so it reaches points on the sensor directly and the fine details stay crisp.
aperture opening f/2.8 – f/5.6
one point of light
fine detail in the photo
details crisp
f/8 – f/11
Sharpness
Good sharpness but a touch softer
Midrange f-number, narrower aperture
The higher the f-number, the narrower the aperture gets. That means light squeezing through the smaller gap then spreads out, so that same point covers more of the sensor. Fine edges and details begin to lose their sharpness.
aperture opening f/8 – f/11
one point of light
fine detail in the photo
edge detail starts to soften
f/13 – f/22
Sharpness
Visibly soft, loss of detail
Highest f-number, smallest aperture
At the highest f-numbers, f/13 through to f/22 (about as small as most lenses go), the spreading will be at its worst. Every point becomes a soft blob, and neighbouring details run into each other, making the whole frame look soft and blurred.
aperture opening f/13 – f/22
one point of light
fine detail in the photo
detail and texture is lost
Rule of thumb
Most Lenses are Sharpest Around f/5.6 to f/8
•Two or three stops down from wide open is the sweet spot for almost every lens.
•Only go past f/11 when you need the extra depth of field more than you need the finest detail, which is often the case in landscapes and close-ups.
•Softness in lens diffraction cannot be reversed in editing. It is a permanent loss of detail.
Want to keep this information handy? Download a free PDF version of the diffraction infographic.
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