Aspheric lenses advantages disadvantages

A decade ago, I was lucky enough to get a 35 f/1.4 "Aspherical" and an "ASPH" together in the same place at the same time, and do a little test.

What they do depends on what the designer wants them to do: improve performance without adding elements, allow fewer elements without reducing performance, allow other elements to correct something other than spherical aberration (chromatic aberrations, astigmatism, etc.)

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Spherical lenses have a surface that is a section of a sphere. That is, they have a constant radius. This makes them easy to grind and polish, especially in mass production.

Note that the APO Sonnar 135/2 is not part of the high-end Otus line, but it is in my opinion the best 135 lens ever made.

And when these lenses are compared, it is clear that what really matters is the overall lens design, rather than the number of asphericals.

Asphericallensvs spherical

When Leica first produced aspherical surfaces (Nocitlux f/1.2, 35mm f/1.4 "Aspherical," not "ASPH") they had to be hand-made one at a time, with a fairly large failure rate (toss the lens and start over).

But since about 1990, better (cheaper, mass-production with a low loss rate) techniques have allowed the addition of aspheric elements throughout the industry. Leica and Hoya jointly developed a "blank-pressing" or molding process whereby soft hot glass is pressed against a metal mold already shaped to the aspheric curve. So that now even inexpensive P&S lenses often have aspheric elements.

This requires additional glass elements that correct the error of the first element, but introduce their own aberrations, and more elements to correct those...etc. etc.. However, for quite a long time, it was still cheaper to pay for the extra bits of glass than to produce one-off aspherical surfaces.

But since about 1990, better (cheaper, mass-production with a low loss rate) techniques have allowed the addition of aspheric elements throughout the industry. Leica and Hoya jointly developed a "blank-pressing" or molding process whereby soft hot glass is pressed against a metal mold already shaped to the aspheric curve. So that now even inexpensive P&S lenses often have aspheric elements.

What they do depends on what the designer wants them to do: improve performance without adding elements, allow fewer elements without reducing performance, allow other elements to correct something other than spherical aberration (chromatic aberrations, astigmatism, etc.)

Thanks for all the easy explanations. Just of out of curiousity, can you please share your thoughts and analysis on Zeiss ones - more specifically Sonnar and Otus lenses. I know some of them are meant for DSLRs.

Hi jip, Take a look here Aspherical so non spherical what is it actually?!. I'm sure you'll find what you were looking for!

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Aspheric meaning

However, a spherical surface is not the best way to form a photographic image, especially with large-diameter (i.e. "fast") lenses. It introduces "spherical aberration" - light coming through the outer edges is not focused at the same point as light passing through the center.

At f/1.4, the Aspherical was a bit sharper in the center and softer in the corners - the ASPH had more even sharpness over the whole image. Net - it would be hard to say one was "better" than the other overall, although the Aspherical might be a bit better for photojournalism (corners don't matter) and the ASPH better when the corners DO matter.

Asphericallensvs normallenscamera

The "Sonnar" name is for a lens design, while the "Otus" name is for a high-end lens line (with different lens designs, currently a Distagon and a Planar).

This requires additional glass elements that correct the error of the first element, but introduce their own aberrations, and more elements to correct those...etc. etc.. However, for quite a long time, it was still cheaper to pay for the extra bits of glass than to produce one-off aspherical surfaces.

When Leica first produced aspherical surfaces (Nocitlux f/1.2, 35mm f/1.4 "Aspherical," not "ASPH") they had to be hand-made one at a time, with a fairly large failure rate (toss the lens and start over).

Just to add a bit of personal experience about the magic of "asph"... in the automotive industry is normal to have aspherical surfaces in the reflectors of front lamps : the need to accord this with style-driven constraints makes the manufacturing of moulds for those components a very delicate and highly specialized job.... btw, CNC machines do not perform, mathematically strict speaking, aspherical tool paths, but very small arcs, continuosly tangent one to the other, with very small variations in radius... tolerancing fixes it all.

Aspheric lenses for astigmatism

Aspheric Lenses price

The 35 f1.4 "Aspherical" will cost you anywhere from $10,000 to $15,000 today. There are several on ebay if one is interested.

Inexpensive lenses reduce aberrations by adding lots of lens elements, but this increases flare. Using asphericals reduce the number of elements which may improve flare suppression

Erwin Puts says one aspheric surface does the work of two spherical surfaces, so two aspheric surfaces can eliminate one entire element (two sides, both spherical). Or improve the lens without adding one whole additional element.

In general, a double-aspherical lens is supposed to be better corrected than a single-aspherical lens. But this may not be the case. Technology always advances, and an improved/better design could use less asphericals for similar performance.

Erwin Puts says one aspheric surface does the work of two spherical surfaces, so two aspheric surfaces can eliminate one entire element (two sides, both spherical). Or improve the lens without adding one whole additional element.

However, a spherical surface is not the best way to form a photographic image, especially with large-diameter (i.e. "fast") lenses. It introduces "spherical aberration" - light coming through the outer edges is not focused at the same point as light passing through the center.

Spherical lenses have a surface that is a section of a sphere. That is, they have a constant radius. This makes them easy to grind and polish, especially in mass production.

Erwin Puts says one aspheric surface does the work of two spherical surfaces, so two aspheric surfaces can eliminate one entire element (two sides, both spherical). Or improve the lens without adding one whole additional element.

Spherical lenses have a surface that is a section of a sphere. That is, they have a constant radius. This makes them easy to grind and polish, especially in mass production.