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09-03-2010, 05:23 AM   #16
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QuoteQuote:
Aspherical lenses combine characteristics that otherwise require multiple spherical elements.
Hum... no. they compensate for the aberrations created by spherical surfaces. That's diffferent.

QuoteQuote:
Well, i'm seeing quite a few lenses with this specific shape being sold specifically as aspherical lenses, some of them even have the word "aspherical" on the side of the lens.
I don't know about the shape, the picture looks like a regular lens to me. But about writing it on the lens, having aspherical elements is a good thing, so it's to be expected that it will be written on the lens.

QuoteQuote:
They are much easier to produce now. Perhaps the moniker "Aspherical" is still used to infer something special.
It IS special. Or at least different. That's what I explained before.

09-03-2010, 06:39 AM   #17
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QuoteOriginally posted by rhodopsin Quote
Aspherical lenses combine characteristics that otherwise require multiple spherical elements. ...
QuoteOriginally posted by bdery Quote
Hum... no. they compensate for the aberrations created by spherical surfaces. That's diffferent.
Hum... yes.

"Aspheres allow optical designers to correct aberrations using fewer elements than was previously possible with conventional spherical optics."

Ref: Aspheric Lens Designs - Edmund Optics

Different?
09-03-2010, 06:56 AM   #18
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"having aspherical elements is a good thing"

there are three types of aspherical elements and they are not all created equal.

First type, Hybrid Aspheric: plastic lens in an aspherical shape bonded with a glass lens, provides reletively good optical correction. Very cheap to manufacture, and that fact shows in the image quality. the Canon EF-S 17-85mm f/4.5-5.6 IS is a lens that makes use of these.

second type : Glass Moulded Aspheric (GMO): just as the name suggests, the aspherical shape is provided by a mould that the glass is injected into. This type is quite commonly used by lens manufacturers due to the ease of mass production.There have been concerns over bubbles being present in the glass, however With modern production techniques this issue has been pretty much resolved. The Pentax FA31mm f/1.8 is a lens that uses a GMO and the correction of aberrations it provides is extremely good,especially in combination with ED glass.

third type: Ground Aspheric : Rarely used, Except in "Ne plus Ultra" lens designs, due to the fact that they are very expensive to produce. Ground aspheric lenses provide a level of correction beyond other lens types. The curvature of the aspeheric surfaces is able to be ground to the extremely fine tolerances required to eliminate lens aberrations. However, this process is slow and requires hand finishing with lapidary techniques. The Noct nikkor 58mm f/1.2 the Nikkor 28mm f/1.4 and the Leica Noctilux 50mm f/0.95 ASPH are lenses that make use of these types of aspherics.

Last edited by Digitalis; 09-03-2010 at 07:11 AM.
09-03-2010, 08:30 AM   #19
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Here is a related recent thread discussing lens terminology.

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/111936-meaning-ed-al-if-lens.html

09-03-2010, 11:42 AM   #20
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QuoteQuote:
"Aspheres allow optical designers to correct aberrations using fewer elements than was previously possible with conventional spherical optics."
I know about Edmunds Optics, I order from them regularly at work. You are saying exactly the same thing I'm saying, in different words. I said aspherical lens elements are used to correct aberrations, just like what your quotation says. It's theoretically possible to correct spherical aberrations using other spherical lenses with opposed curvature, but it's not practically possible if you want to preserve resolution, aperture, etc. In real life it almost never is done.

QuoteQuote:
there are three types of aspherical elements and they are not all created equal.
That's true. Just like any lens, aspherical lenses or lens elements can be made in a number of ways. I don't dispute that.

For the record, photographic lenses are almost always ground.

(I,m not talking about cell phones cameras and the like, of course. those are not really "cameras" )
09-03-2010, 11:55 AM   #21
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QuoteOriginally posted by Silverkarn Quote
A lens like this:
28-200, and its so short. the lens extends to zoom instead of you moving a slide back and forth to zoom.
Is something wrong with these that EVERYONE doesnt have just one in their lens collection?
Uh, I honestly don't know ANY DSLR owners who don't have a zoom with aspherical elements in some form or another.

As for super zooms with that high a multiplier. That is less common. There's no free lunch. Although the pentax 28-200 isn't a horrible compromise.
09-03-2010, 01:10 PM   #22
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Hoya info

Optical Glass and Lens Pressings from HOYA OPTICS: Leading supplier of advanced optical materials & components

interesting videos

http://www.canon.com/camera-museum/tech/l_plant/main.html

Canon Camera Museum | Technology Hall | Virtual Lens Plant

Additional information

HOYA CORPORATION|About HOYA

Last edited by Blue; 09-03-2010 at 01:24 PM.
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