Does lens sharpness change at different apertures?
Asked 7/16/2012
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Is there usually a noticeable change in image sharpness as you stop a lens down? I'm using a Canon 550D with the kit lenses and want to know whether some f-stops are sharper than others, and how I can find the sharpest aperture for my lens.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
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Yes. Generally lenses are at their worst wide open or stopped right down. The former is especially the case when it comes to cheaper zoom lenses. Most lenses have a 'sweet spot' where quality is best - an f4-5.6 lens usually has a sweet spot around f8-11. A relatively cheap 1.8 prime usually has a sweet spot around 2-3.5
More expensive lenses are generally much better wide open - it's one of the reasons they're more expensive.
Regardless of the lens quality, they will all suffer a loss of sharpness at the higher f-stops (f16 and up) due to diffraction - see this question for more on that.
Originally by user3205. Source · Licensed CC BY-SA 4.0
user3205
14y ago
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Generated from our catalog & community — verify before relying on it.
Yes. Lens sharpness usually varies with aperture.
In general, many lenses are softer at their widest aperture, especially inexpensive zooms and kit lenses. Sharpness often improves as you stop down a little, reaches a “sweet spot,” then falls again at very small apertures because diffraction reduces fine detail.
A common rule of thumb is:
- kit zooms: often best around f/8 to f/11
- fast primes: often best a couple of stops down from wide open
More expensive lenses are often better wide open, but even they can lose sharpness at very small apertures such as f/16 and smaller.
For your Canon 550D kit lens, the simplest way to find the sharpest aperture is to test it yourself: photograph the same detailed subject from a tripod at each aperture, keep focus and framing unchanged, then compare the images at 100% on your computer. That will show where your specific lens performs best.
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