How do aspherical lens elements affect image quality compared with spherical designs?
Asked 1/15/2015
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I’ve read that aspherical elements differ from spherical ones geometrically, but what does that change in actual photos? What visible differences should I expect in sharpness, glow/haze, corner performance, or bokeh? Also, if a lens is advertised as having an aspherical element, does that simply mean it uses one method of correcting aberrations, while other lenses may use different designs or may not list it prominently?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
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Geometry is a big part of optics. Don't think of it as something other than the picture, it's what makes the picture.
An aspherical lens does not suffer (so much) from spherical aberration. That's a fancy term for "the rays of light do not meet exactly in one distance from the lens". But what's exactly in one distance from the lens? Right, the sensor or film of the camera. If you have spherical aberration in your image, some parts of it will be blurry (out of focus) even if they should be sharp because the rays do not meet each other exactly on the sensor (they meet a bit in front or behind it). The further from the sensor the rays come into the lens, the more pronounced will this problem be.
That's why the cool kids are always bragging about the corner sharpness of their lenses. That's where it pays off to have aspherical lens.
Well, "advertised as" plays an important role here. It sounds technical and can attract buyers. Lenses are often lens systems that are made out of several elements. Usually not all elements are aspherical, because the production of such elements is more expensive than the spherical ones. Optical systems have a lot of properties you don't even hear about or only hear about insufficiently making them useless for comparison.
For example: a lot of lenses have a stabiliser, to prevent camera shake. But how does one compare to the other? The information is limited to them having a stabiliser. What exactly does it mean to have weather sealing? Can it be dropped in the mud, used in a hail storm or what?
But sure enough, not mentioning them will make your product look worse than those of other vendors.
Don't worry so much about these marketing buzz words. If you are not sure what lens to buy, read about them. This will give you an estimate of their strengths and weaknesses. If you still can't decide, rent both. Preferably at the same time and compare them for yourself.
And remember that it's you who takes the picture, not the asphericitillityness* of your lens.
*that totally is a word
Originally by user35348. Source · Licensed CC BY-SA 4.0
user35348
11y ago
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Generated from our catalog & community — verify before relying on it.
Aspherical elements are mainly used to reduce spherical aberration—light rays from different parts of the lens focus more accurately onto the sensor. In photos, that usually means:
- better sharpness, especially at wide apertures
- less glow/haze when shooting wide open
- improved edge/corner sharpness
- more even focus across the frame
With more spherical aberration left uncorrected, lenses often show:
- softer rendering wide open
- a glowing/hazy look at large apertures
- smoother background blur, but harsher foreground blur
With stronger correction using aspherical elements, lenses often show:
- cleaner, crisper wide-open images
- background and foreground blur that look more similar
- sometimes slightly harsher bokeh than less-corrected designs
- in some cases, concentric “onion ring” patterns in blur circles from some aspherical elements
So “aspherical” doesn’t mean the whole lens is fundamentally different; it usually means one or more elements are shaped that way to help correct aberrations. If another lens doesn’t mention it, that may mean it uses other corrections, fewer aspherical elements, or the maker simply doesn’t emphasize it in the marketing.
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