Aspherical lenses What is it and what are the available options.
What is it ?
Lately, I am disturbed by some marketing kit which carries a lot of advertisement that talk about lenses with Aspherical lens elements. These manufacturers are pushing hard and aggressively promoting a new breed of lenses that carries with a tag called Aspherical Lens..
Sometimes, these advertisements can make public look suspiciously at their current lenses in the camera bag and generate a uneasy feeling of owning some inferior quality lenses which are without an aspherical lens elements.
Some bought the idea and disposed off theirs and rushed for an upgrade even that came at similar focal length and lens type. This prompt me to find out some basic resources relates to this and compiled here for everybody to consume and see if it benefits and calm you down a little.
Aspherical lenses incorporating some optical characteristics. These lenses are small, lighter and in general, better than similar lenses which only employ spherical elements. In some instances, using an aspherical element enable the lens designer to use fewer lens elements. The benefit can be a smaller, compact and lighter lens; with fewer lens surfaces, there is also less potential for internal reflection - that is why there are more and more zoom lenses incorporating a (or few) aspherical lens element within to substitute a number (Depends on optical design).
To a manufacturer, it means it can be cheaper to produce a lens, besides, while along the way, optical performance can be improved as well (Theoretically). Basically, they are thinking of ways to be more competitive on the market place and after the investment in the manufacturing processes of producing aspherical lens elements, naturally, this becomes a marketing tool to boost the sales and get the fastest return on investment.
Simplest way to illustrate what a aspherical lens element is all about.
Technically, an aspherical lens is a lens whose curved surface does not conform to the shape of a sphere; lenses are usually ground or molded with spherical surfaces; because a spherical surface lens has difficulty in correcting distortion in ultra-wideangle lenses or coma in large-aperture lenses brought about by spherical aberration, an aspherical lens is used. Where in the case of zoom lenses, a lens element or two can substitute a bigger number of lens elements to achieve similar or better optical results and to reduce the overall cost of production and more compact of the size of a lens - especially in the case of zoom lenses, where lens elements of more than 10 are not too unusual.
Simplest way to illustrate what a aspherical lens element is all Spherical aberration of a spherical lens and convergence of parallel light rays with the use of a aspherical lens element.about.
A 28-105mm f2.8/4 Sigma lens with aspherical elements in its optical design.
Generally, for the vast majority of even the most demanding applications, conventional lenses are much more than adequate. Where previously, due to the high cost and tedious production process of producing aspherical lens elements, most manufacturers who has the technology to produce these elements only restrict the use of aspherical surfaces to lenses where they are essential.
Anyway, the existence of aspherical lens has been quite a while on the market. Like the time honored Noct-Nikkor 58mm f1.2 and the discontinued OP-Fisheye Nikkor 10mm f5.6 from Nikon has been around for almost two decades are just two classical examples. Each representing lenses for some specific applications, like general or scientific/Industrial use.
The OP-Fisheye Nikkor 10mm f5.6 is one of the earliest in Nikkor family to use an aspherical lens front element to ensure its mathematically correct illumination pattern.
Recent development of seeing more and more exciting lenses made possible after individual manufacturer found various solutions in manufacturing process to produce aspherical lens elements. Tamron developed a method of apply and treating an optical resin to normal spherical surface of a lens to made it aspherical; Nikon overcame its problem in grinding etc..all these accounted for the sudden emergence of lenses of all types with a or a few aspherical lens elements within.
Among the top five camera manufacturers in Japan, Canon is the most aggressive among the few to push the technology into their EF-L series lenses. Although many may not realize, the world's first SLR lens to have an aspherical element incorporated within was a FD 55mm f1.2 AL SSC.
Fast lenses, at times has problem maintaining its optical performance at widest opening, especially in situation where the illumination is dim. A aspherical lens can assure optimum correction of coma. Like images of scenes with small points of light - bright point sources of light near the edges of the picture appear as dots rather than comet-shaped blurs. Some newer generation of fast lens, like the world's fastest 28mm lens, the AF Nikkor 28mm f/1.4D, or the recent Canon's super fast EF 50mm f1.0 L use an aspherical element to ensure compact size and to obtain superb performance by eliminating sagittal, or arrow shaped, coma, even at its widest aperture.
Sometimes, the light passing through the central area of a lens cannot be focused at precisely the same plane as the light passing through the peripheral areas. This is a spherical aberration that makes sharpness inconsistent. While this phenomenon is not always a problem, some lens designs can be significantly improved to higher levels of overall sharpness through the use of aspherical elements.
Tamron's Aspherical lens 28-200mm f3.8/5.6 LD IF is only 3.2" in length. First started the 28-200 compact zoom revolution in 1992, current version packs all modern features like low dispersion glass, internal focus and aspherical lens surface.
Another 3.2" compact offer from Tamron, the SP AF20-40mm F/2.7-3.5 Aspherical (IF). Packing features like dual aspherical elements: Large diameter Hybrid Aspherical elements are used in the front focus group to substantially compensate for distortion aberrations at wide angle. Another Hybrid Aspherical element added to the rear group effectively eliminates comatic flare.
Though early days, the concept of adoptions of aspherical design were to certain specialized lenses where its benefits can be fully realized in specific applications. But since with the wide acceptance and popularity of zoom lenses by many serious SLR users nowadays, you will be rest assured that new generation of aspherical zoom and prime lenses will be coming in with more "varieties" and economically - in a grand scale.
The solid AF Nikkor 28mm f1.4D is not cheap, one of the first few new generation of AF- Nikkor from Nikon came with an aspherical lens element.
Current manufacturing precision standard which can have a tight tolerance of asphericity to be within 0.1 micron and thus popularizing the broad usage of aspherical lens elements for optical designers. Anyway, the topic has become a selling point for many optical lens producers, those marketing guys might do whatever it takes to sell you the idea of substituting your current lenses in your camera bag now. And there is a strong possibility that most new higher grade zooms will have a element or few within in time to come (because once the floodgate is opened, the rest without a aspherical element won't be selling well). And we will benefit from it.
First affordable compact Nikkor zoom to utilize an aspherical element within. The AF Zoom Nikkor 28-70 f3.5/4.5 D, definitely will not be the last from Nikon.
Think of rushing out to get one or replacing your current lenses ? No necessity We have forgotten those older SLR lenses that were out there since the late '50 have produced millions of faithful, good and stunning images that has impressed all of us and there is absolutely no hurry to change unless you have lost, spoilt or damaged yours and looking for a fresh replacement. Well, it is just a fruitful product along with the natural course in the lens development and technology.
The bottom line: What does it mean to all of us ?
Wait and use your existing lenses.
Reasons ? Refer above.
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