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Thread: Is aspherical element in lenses bad?

  1. #1
    Verre Vrai
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    Smile Is aspherical element in lenses bad?

    Read from some sources that mentioned aspherical lens is not as good as true glass lens, what do you guys think? With aspherical element build into the lens, size can be dramatically reduced, but some pro photographer argue that quality is compromised, or it is?

    P.S. Almost all the Digicam in the market uses aspherical lenses.
    Last edited by Verre Vrai; 28th October 2002 at 09:25 PM.

  2. #2

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    Huh? Who said this? Aspherical and glass are not mutually exclusive (i.e, you have aspherical glass elements). And aspherical elements do not dramatically reduce size or anything. Aspherical elements are used to reduce/eliminate spherical aberration and distortion for higher optical quality. Read up here : http://www.canon.com/camera-museum/t...m/f_index.html

  3. #3
    Verre Vrai
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    Originally posted by sriram
    Huh? Who said this? Aspherical and glass are not mutually exclusive (i.e, you have aspherical glass elements). And aspherical elements do not dramatically reduce size or anything. Aspherical elements are used to reduce/eliminate spherical aberration and distortion for higher optical quality. Read up here : http://www.canon.com/camera-museum/t...m/f_index.html

    The correction of aberration and distortion is normally corrected by ED glass (Extra-low Dispersion glass) lenses, Aspherical element is used to reduce size and weight and does correct spherical aberration but also got other problems. Canon can say what they like, that is manufacturer's saying because they want you to buy their stuffs and cut production cost to maximise profit. Try to read from neutral sites. One of them

    http://www.mir.com.my/rb/photography...aspherical.htm

    Another one from http://www.imx.nl/photosite/leica/rs...tr/r14-50.html

    "The ASPH riddle.
    Leica has introduced in recent years several lenses with one or two aspherical surfaces. Generally the image quality of these designs is quite high, to say the least. Some observers of the Leica scene have erroneously concluded that the equation aspherical=high image quality now has universal validity. Some even went further and deduced that any lens design without an aspherical surface can not be designated as a modern design. Occasionally one will hear or read the statement that for example the current Summicron 50 lens for the R series is an old design and needs or will be superseded by a newer design of invariably aspherical signature. It is easy to be charmed by such reasoning. This assumption, however, is not correct. First some facts. One: the new Summilux-R 1,4/50 (subject of this report) has been designed with conventional means. We can then conclude that the Leica designers could realize the required level of image quality without recourse to aspherical surfaces. If the use of asphericals would have been advantageous for the state of corrections and the production requirements, Leica certainly would have incorporated them. Two: aspherics are not always the best way to go. The Ricoh 28mm uses two aspherical surfaces but its image quality is below that of the Leica
    28mm and the Zeiss 28mm for the G-series, both without asphericals. Three: all Zeiss lenses for the G-series are quite recent designs and none of them has any aspherical surface. The image quality of these lenses is beyond any reasonable doubt.

    One of the main reasons for employing asphericals is the correction of spherical aberration and attaining a flat field free of astigmatism. But the use of asphericals may also affect other aberrations in a dangerous way, especially if the distance between diaphragm position and aspherical surface is relatively large. The design of an optical system must always try to balance many demands and variables, some of which are optical and some of which are manufacturing oriented. It could be that a designer tries to incorporate an aspherical surface only to find out that the strain on production tolerances is too heavy. He also could note that given the overall configuration of his/her design, the aspherical surface has no added value, or even will enlarge or introduce other aberrations. Note that any optical system must be regarded as a delicate whole of carefully designed and matched components. Note also that all aberrations act on every image point in conjunction. Note further that ”„image quality”¦ is not a fixed set of parameters. Zeiss will adjust the balance of corrected aberrations and the magnitude of corrections according to different rules than Leica does. Leica may conclude than given the required correction in some cases aspherical surfaces are justified and in some cases not."


    Do a search for "Aspherical lenses" and you can find many many info about it.
    Last edited by Verre Vrai; 29th October 2002 at 12:50 PM.

  4. #4
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    I think aspherical is used for shortening the required spaces between elements hence lighter and less glass needed... since APO corrects distortion the other elements can distort all they want, vs a balanced set of glass... but of cos once scattered the rays might not be nicely aligned with some permanent shift at the extremes, rims etc...
    BUT, again it's up to you to want a set of Primes at f1.0-2.8 vs a 50-500 zoom that doesn't look like Hubble the Pink Telescope...
    "I'm... dreaming... of a wide... angle~
    Just like the ones I used to know~"

  5. #5
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    Default Re: Is aspherical element in lenses bad?

    Originally posted by Verre Vrai
    Read from some sources that mentioned aspherical lens is not as good as true glass lens, what do you guys think? With aspherical element build into the lens, size can be dramatically reduced, but some pro photographer argue that quality is compromised, or it is?

    P.S. Almost all the Digicam in the market uses aspherical lenses.
    With regards to your statement above, it's simply not true as there are some stunning lens designs that cannot be manufatured without aspheric lens surfaces. Also there are lenses that use glass aspheric surface elements as well as those made from optical plastics and the glass aspheric lenses are every bit as good as 'glass lenses' as they ar glass

    A couple of lenses to have a look at that demonstrate how good aspheric surface lens design can be:

    Nikkor 300mm f2
    (not a confirmed aspheric element at the 4th spot, but it looks like one, and no I'm not going to take the lens apart to find out1)

    Nikkor 17-35 AFS
    Nikkor 28-70 AFS
    Nikkor 14mm f2.8
    Nikkor 20-35 f2.8

    There would be very few people who wouldn't evaluate the lenses above as being either best in class or damn close to it.

    It might help if you know that aspherical elements have been around for at least 100 years, there's nothing new about them or their uses in optical design.

    The main benefits to a lens manufacturer of using aspheric elements can be:

    1) Improved optical performance

    2) Reduced optical complexity (ie: fewer lens elements required)

    4) Allows the use of exotic computer generated lens systems and solves the often horrific abberations that would otherwise occur (eg: spherical induced abberations, which apply to colour shifts, coma and spherical abberatio itself.

    What this all leads to is a lens that's cheaper to manufacture, sells for less and keeps the consumer happy. It doesn't however make the lens a better performer.

    Many of the traditional lens designs, such as the Gauss, double Gauss, Petzval, symetrical (triplet) and quasi symetrical, symetrical (4 element designs) and so on are damn hard to beat in fixed focal length lenses.

    However it's really with zoom lenses that aspheric surfaces come in to the fore, in particular in the realm of offering improved performance and reduced costs.

    A case in point, I recently evaluated the 14/2.8 Nikkor, it's a lovely lens, not quite as good optically as the old 13/5.6 Nikkor (ie slightly more distortion), but the 14mm is two stops faster, has more contrast, weighs 1/2th the weight and is 1/5th of the cost of the old 13mm. So which lens is the better bet?

    However I also agree wtih your second post, there are times when the use of aspheric elements does seem pointless and in many cases they are used as stated earlier in this post, to reduce optical complexity, and cost, often at the expense of image quality when compared to a more traditional design.

    So in the end, aspherics have a place in the lens world, yes they can outperform older designs and no, they aren't always needed, nor are all designs using them going to be 'better' becase of the use of aspheric surfaces. In the end it comes down to what the photographer requires, is willing to pay for and the level of performance they want and the abilities of the optical designer to deliver the goods.
    The Ang Moh from Hell
    Professional Photography - many are called, few are chosen!

  6. #6

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    Originally posted by Verre Vrai
    The correction of aberration and distortion is normally corrected by ED glass (Extra-low Dispersion glass) lenses, Aspherical element is used to reduce size and weight and does correct spherical aberration but also got other problems. Canon can say what they like, that is manufacturer's saying because they want you to buy their stuffs and cut production cost to maximise profit. Try to read from neutral sites.
    Well aspherical optical elements do serve to lower weight by reducing the number of elements if you look at it that way, but the individual elements themselves need not be any lighter.

    Bottom line : whether you use aspherical elements or not, the quality of the lens depends on many more things. For example the Sigma 28-70/2.8 EX has aspherical glass, but the sample I tested suffers from lots more spherical aberration (specially away from the centre) compared to the Tokina AT-X Pro 28-80/2.8. Quality control, manufacturing tolerances and overall design matter a lot more.

    I am not sure about other extreme lenses, but the Sigma 15-30 I used shows really weird "smearing" (for lack of a better word) effects away from the centre - where an object is stretched and distorted. This lens too has aspherical elements. So... quality control and tolerances again.

    Like you say, manufacturers can claim to use whatever they want (Apo, Aspherical optics, etc) but how good are they, really? For example, many manufacturers claims of using Apo glass are really pushing the limit. I seriously doubt Sigma's "Apo Macro DL DX DG whatever" lenses are really true Apochromat designs like Leitz/Zeiss glass.

    That said, it is more likely that big name OEM guys like Canon, Nikon etc would produce higher quality Aspherical elements for their high end lenses compared to third party lens makers. So.... there's quite some truth in Canon's (or Nikon or Minolta whatever) statements.

    BTW Erwin Puts' site at imx.nl... the one you referred to, is not really "neutral" if you read through the entire site. He's a known Leica fanatic.

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    wa all the posts here r long......lay.....can sum up a bit next time??

  8. #8
    Verre Vrai
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    Originally posted by roti
    wa all the posts here r long......lay.....can sum up a bit next time??
    This kind of "cheem" topic is difficult to keep it short mah.

  9. #9
    Verre Vrai
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    Originally posted by denizenx
    I think aspherical is used for shortening the required spaces between elements hence lighter and less glass needed... since APO corrects distortion the other elements can distort all they want, vs a balanced set of glass... but of cos once scattered the rays might not be nicely aligned with some permanent shift at the extremes, rims etc...
    BUT, again it's up to you to want a set of Primes at f1.0-2.8 vs a 50-500 zoom that doesn't look like Hubble the Pink Telescope...

    Let alone Hubble the Pink Telescope, I dun think I 'll even lug around that Canon 1200mm monster ...

  10. #10
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    Originally posted by sriram

    BTW Erwin Puts' site at imx.nl... the one you referred to, is not really "neutral" if you read through the entire site. He's a known Leica fanatic.
    agreed. I refer a lot to what he write too, since he really does know his stuff, and i believe in his testing methods, which he clearly outlined. (but NOT his choice of nude models for such tests!)

    BUT his writings reveal his biasness towards all things Leica, even when he admits the competition is better in some aspects (Voigtlander's Nokton 50mm f1.5, for example).

    You know something is seriously wrong when one refers to the "soul of Leica lenses". this is the kind of stuff marketing depts will come out with

    Recently, he wrote an online book about Leica lenses for Leica (which is available on the Leica website), and that raises a lot of questions about his neutral status, one which he has claimed so far.

    So the solution is always check with multiple sources, instead of relying on one....... and draw your own conclusions from there..
    David Teo
    View my work and blog at http://www.5stonesphoto.com/blog

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