What does aspherical mean ?

[ColdDuck 0]

Just out of curiousity what does the term aspherical mean? I am looking at a 18-35mm aspherical camera lense.

Thanks

"Insurance should called In case shit happens, if shit don't happen shouldn't I get my money back?"

[LouDiamond 1]

Main Entry: aspher·ic
Pronunciation: (")A-'sfir-ik, -'sfer-
Variant(s): or aspher.i.cal /-i-k&l/
Function: adjective
Date: circa 1922
: departing slightly from the spherical form especially in order to correct for spherical aberration

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[ColdDuck 0]

en ingles por favor!

"Insurance should called In case shit happens, if shit don't happen shouldn't I get my money back?"

[AndyMan 7]

Think: Walley-vision in a big way.

_Am

__

You put the fun in "funnel" - craichead.

[murrays 0]

The lens uses an aspherically (non-spherical) shaped element or elements to correct for spherical aberrations which degrade the image. Very common in lens design.

What make of lens are you looking at buying?

--
Murray

"No tyranny is so irksome as petty tyranny: the officious demands of policemen, government clerks, and electromechanical gadgets." - Edward Abbey

[ColdDuck 0]

It is a Sigma 18-35mm

"Insurance should called In case shit happens, if shit don't happen shouldn't I get my money back?"

[LouDiamond 1]

Main Entry: spher·i·cal
Pronunciation: 'sfir-i-k&l, 'sfer-
Function: adjective
Date: 15th century
1 : having the form of a sphere or of one of its segments
2 : relating to or dealing with a sphere or its properties
- spher·i·cal·ly /-k(&-)lE/ adverb


Main Entry: ab·er·ra·tion
Pronunciation: "a-b&-'rA-sh&n
Function: noun
Etymology: Latin aberrare
Date: 1594
1 : the fact or an instance of being aberrant especially from a moral standard or normal state
2 : failure of a mirror, refracting surface, or lens to produce exact point-to-point correspondence between an object and its image
3 : unsoundness or disorder of the mind
4 : a small periodic change of apparent position in celestial bodies due to the combined effect of the motion of light and the motion of the observer
5 : an aberrant individual
- ab·er·ra·tion·al /-shn&l, -sh&-n&l/ adjective

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[newshooter12 0]

my boss wanted to sell me a Sigma lense like that... for $125 USD.Then he decided that he liked it too much.
Oh well I'll wait for his next hand-me-down.
matt

[alain 0]

aspherical on a slr lens means that it includes some no spherical elements in order simplify the design of the lens (ie less elements) and make it lighter.
Eventually it will increase the over all performance of the lens or make possible a wide focal range on a zoom that would not be possible with only traditional spherical elements.
An element is spherical when it's shape corresponds to a radius. when not, it is aspherical.
Aspherical elements appeared with high precision digital machinery allowing to make them easily and consistently.
You will find aspherical elements almost anywhere nowadays 'coz they are becoming cheap to built but they don't always mean high performance. The key is high accuracy in aspherical design and manufacturing and high glass quality, witch means higher cost, as usual...

the "aspherical tag" can be only commercial appeal: quite impressive for those who don't know what it means
Sigma's are usually pretty good (I couldn't say for this one specifically as I never used it) and fairly priced.

the "valley vision" is called barrel distortion and is not directly linked to spherical or not elements: it's only caused by poor design. (except on fish eye lens, where this effect is expected)

'hope this helps...

Alain