What is meant by aspherical lens?

[GrantEb]

Hi all

Just wondering if anyone could explain how a std photographic lens would differ from an Aspherical lens? Would it be beneficial for astro work?

TIA

cheers

[Demonperformer]

Seems they are good at eliminating aberrations that would normally require several elements: Aspheric lens - Wikipedia, the free encyclopedia

[GrantEb]

Thanks DP.

I guess it would come down to an actuall test of a specific lens in the end.

Cheers

[FraserClarke]

Most lenses have a spherical surface, because they are far easier to make and test. If you're good enough at making lenses, you can change the shape of the lens surface to correct other aberrations, but it's much harder to do and to test -- hence it costs a lot more. Direct analogy is a parabolic (aspheric) primary mirror compared to a spherical primary mirror.

In theory certainly an advantage for astro, because you can have fewer lenses and hence higher transmission; but you're going to pay for that extra few percent efficiency.

[ollypenrice]

I have a couple of aspherical camera lenses which do well in astronomical applications. The faster the f ratio the greater the need to deviate from the spherical, I believe.

Olly