Understanding the Aspherical Lens in Photography (Asph Lens)

Ever wonder what the difference is between an aspherical lens and a “normal” spherical lens?

Maybe you’re looking at buying a new lens and aren’t sure if you should fork out the extra cash for the one marked “Asph Lens,” or you’re just wondering what makes aspheric lenses expensive.

Either way, knowing what an aspherical lens is and what it does will help you in better understanding your gear and when it comes time to purchase new types of camera lenses, you’ll have a better idea of what to buy.

So let’s take a look at the aspherical lens, what it does, and why it just might be worth that extra hit to your wallet.

What is an Aspherical Camera Lens?

An aspherical lens is simply a lens that doesn’t have a spherical surface shape. Instead, it has an aspheric surface (i.e. non-spherical), usually with counter-curves near its edges.

These counter-curves direct light rays hitting the edges of a lens to converge at the same point of focus as the light rays hitting the center.

Standard lenses use spherical elements, many of which aren’t natively able to direct the light reaching its edges to the same focal point as the light reaching its center.

Designers – especially with wide-angle lenses – often have to stop-down their optical systems to exclude the corners so as to avoid an excess of field curvature.

The lens surface of an aspherical lens corrects for this, making it possible to shoot at wider apertures and allowing us to use the entire surface of the lens.

What is an Aspherical Camera Lens Used for?

Aspherical lenses are used primarily in high-end optics to create sharper images and reduce or eliminate certain optical imperfections (i.e. chromatic aberrations, field curvature, etc.).

They also allow manufacturers to create smaller and lighter lenses since they reduce the need for numerous lens elements and lens groups.

As you can imagine, aspherical lenses aren’t just used in cameras. They’re a vital part of any system that needs a high standard of optical quality, from telescopes and contact lenses, to rifle sights and missile-guidance systems.

Aspheric eyeglass lenses are especially useful in combatting astigmatism.

Spherical and Aspherical Lenses: What are the Differences?

1. Physically, spherical lenses have a front surface that is spherical, meaning the curve is the same from top to bottom and left to right – like a portion of a sphere.

Aspheric lenses, on the other hand, have curves that deviate from the regular spherical curve.

2. Aspherical lenses are much more challenging to manufacture. The result is a much deeper hit to your wallet!

The aspherical glass lenses used in top-of-the-line telephoto and wide-angle lenses are particularly expensive. They’re usually ground and polished by hand.

Less expensive aspheric lenses – like those used in point-and-shoots – will often be made of plastic or resin.

3. An aspherical lens element has much more precise control of how light travels inside your lens. So much so, that one asphere can oftentimes negate the need for many of the standard lens elements that would otherwise be needed to achieve the same effect.

The result?  A much lighter, more compact lens.

What is Spherical Aberration?

Ideally, light rays, when passing through a camera lens element, would all converge at a single point thereby creating a sharp focus. Unfortunately, this isn’t the case with many spherical lenses.

Spherical aberrations occur when incoming light rays pass through a spherical lens and focus at different points, causing blurry images and reducing overall image quality.

One way to compensate for this is by using a combination of concave and convex lens elements. Another way is by using an aspheric lens.

Aspherical lenses are curved outwards on their rear element so that they can better direct light rays into a single focal point. These counter-curves help correct spherical aberration, creating sharper images.

Advantages & Disadvantages of Aspheric Camera Lenses

Are aspherical camera lenses better than normal camera lenses?

Absolutely! They’ll make your lens lighter, your images sharper, and bring aberrations and distortion down to near zero. The only downside is how much they cost.

In the past, only pros could afford such top-of-the-line optics. These days they’re still spendy, but at least they’re not completely the ballpark for ordinary photographers.

Final Words

It’s really amazing how far modern optics have come. Not too long ago, only pros could afford full-frame cameras and aspherical lenses. Now those of us in the prosumer world can get them too.

Of course, asph lenses are considerably more expensive than spherical lenses, but high-quality glass will last a lifetime, so if you can spring for the high-performing lens, go for it!

What do you think? Where do you stand in the aspheric lens vs normal camera lens debate?

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