Why can photos look softer at longer focal lengths like 300–500mm?
Asked 12/13/2016
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I understand that lens quality matters, but why do images sometimes seem less sharp at longer focal lengths such as 300–500mm? What factors make telephoto shots look soft, and is this caused by the lens itself or by shooting conditions and technique?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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Several focal-length-related factors can influence sharpness:
It is usually harder to manufacture long focal lens, so at constant cost, expect a 50 mm to be sharp, a 200 mm to be not-so-sharp, and >300 mm to be really low quality.
On a related note, it's hard to make a lens with both a long focal lens and a wide aperture. So, long focal lens often have a narrow aperture, hence more diffraction.
Long focal lens implies shallow depth of field, so any focus imperfection (front or back focus) is much more noticeable.
Long focal lens implies more motion blur except if you use a tripod or have a very fast shutter speed.
Long focal length are often used to shoot distant subjects, in which case the atmospheric effects can be important. Depending on the distance and weather, the atmospheric effects can be the limiting factor, and then whatever the lens, you'll always get bad pictures (thanks @mattdm for the hint, I forgot this one).
Originally by user40449. Source · Licensed CC BY-SA 4.0
user40449
9y ago
0
Generated from our catalog & community — verify before relying on it.
Long focal lengths are not inherently soft, but several things make softness more noticeable at 300–500mm.
First, telephoto lenses are harder and more expensive to design well. Budget long zooms often lose sharpness, especially at the long end. High-end telephoto primes and pro telephoto zooms can be very sharp.
Second, depth of field gets shallower as focal length increases, so even small focusing errors become obvious.
Third, camera shake and subject movement are magnified at longer focal lengths, so you often need a faster shutter speed or better support.
Fourth, many long lenses have relatively small maximum apertures, and stopping down too far can introduce diffraction.
Fifth, telephoto shots are often made over long distances, where haze, heat shimmer, and other atmospheric effects can reduce apparent sharpness.
Finally, optical issues such as chromatic aberration can be more visible in some telephoto images, especially along high-contrast edges.
So the “softness” may come from lens quality, focus precision, motion blur, diffraction, atmospheric conditions, or optical aberrations—not simply from the focal length itself.
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AI9y ago
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