Aspherical lens

[AlQ]

Is there any downside to the quality of an aspherical lens, or is that just the way it is manufactured?

I'm looking at the Tamron 17-50mm f/2.8 which has better reviews than the VC version.

thanks!

[sk66]

They are different things...VC is image stabilization and aspherical is a lens shape...
aspherical generally produces better images across the fov but it won't have image stabilization (I guess)

[AlQ]

So aspherical is a better quality of glass, based on the way it's manufactured?

...and should I assume that if a lens is not advertised as "aspherical" it consists of regular elements?

[LoveDSLR]

According to Nikon.

"The aspherical lens has a curved surface that is not spherical and has the ability to correct aberrations."

[inkista]

Originally Posted by AlQ

So aspherical is a better quality of glass, based on the way it's manufactured?

Not necessarily. Aspherical just means the lens has an element in it that's not shaped to a spherical curve. That's it. Marketing speak basically makes it sound like it's a superior feature you long to have in any lens, but these days, nearly all good lenses have aspherical elements. The best description I've seen on what aspherical elements are and can do for you is in this lensrental article:

... Aspherical elements help focus edge and corner light rays sharply, preventing coma distortion (smearing that makes points of light look like a comma) and other distortion, especially in wide angle and wide aperture lenses. ...

...and should I assume that if a lens is not advertised as "aspherical" it consists of regular elements?

No. If you're really really interested in seeing whether a lens has aspherical elements or not, try and find the design block diagram for the lens. Like this one (again, scrounged from a lensrentals article):

Tamron 17-50/2.8 (non-VC) on the left, VC version on the right:


This shows that the two lenses have different optical designs, which explains why the performance is different between the two. But you'll also note that more is not necessarily better. The VC version has three ASPH elements, while the non-VC only has two.

[AlQ]

great explanation, thanks!