How can I get sharper focus on faces when shooting a 50mm lens at f/1.8?
Asked 10/10/2017
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2 answers
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I’m using a Canon EF 50mm f/1.8 on an EOS 200D. When I shoot portraits at f/1.8, I often struggle to get the face perfectly sharp, especially if the person moves slightly between shots. I’ve tried Dual Pixel AF in Live View and the center AF point through the viewfinder.
With a tripod and a still subject, focus looks good, so it doesn’t seem like a camera or lens defect. Is this normal for fast lenses used wide open, especially budget ones? Or are there techniques that improve hit rate when shooting people at f/1.8?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
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Is this simply a characteristic of cheap wide-aperture lenses?
It is a characteristic of this particular lens, and in general for most fast lenses, that they tend to exhibit more softness when wide open than when stopped down. The EF 50mm f/1.8 STM has its "sweet spot" in the f/4-5.6 range.
That doesn't mean you shouldn't ever shoot the lens wide open, but you do need to understand you're making compromises on sharpness, vignetting, and chromatic aberration when you do. And you probably shouldn't shoot with it wide open by default. Especially as the wider the lens is open, the thinner your depth of field becomes, and the harder it will be to accurately autofocus the lens.
See also: Why are my photos not crisp?
Originally by user27440. Source · Licensed CC BY-SA 4.0
user27440
8y ago
0
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Yes—this is normal. At f/1.8, depth of field is very thin, so even slight subject movement can shift focus off the eyes or face. That makes wide-open shooting harder with any fast lens, not just inexpensive ones.
Your 50mm f/1.8 is also typically softer wide open than when stopped down; lenses like this often look best around f/4–f/5.6. Wide open, you’re trading some sharpness for more background blur and light.
Since your results are good on a tripod with a still subject, the main issue is likely focus precision and subject movement rather than a defect. The EOS 200D’s autofocus system is fairly basic, and only the center point is the most sensitive option.
To improve results:
- use the center AF point when shooting through the viewfinder
- focus on the eye closest to the camera
- avoid focus-and-recompose at very shallow depth of field
- stop down a little (for example f/2.2–f/2.8) for a better hit rate
- take short bursts, since tiny movements can change focus
So: sharp focus at f/1.8 is possible, but it’s demanding and never perfectly consistent with moving subjects.
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AI8y ago
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