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This question already has an answer here:

I know there are lenses like f/0.7

However as a beginner I'm wondering what's the barrier of making ultra fast lenses like f/0.01 ?

Also if lens manufacturers willing to make wide aperture lenses, why it become more expensive? What factor makes it more costly?

marked as duplicate by Philip Kendall, Paul Cezanne, NickM, mattdm, AJ Henderson Aug 20 '14 at 15:17

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Lifting the relevant section from another answer of mine:

Basically, the larger the aperture is, the larger the angle of light rays on the outside of the lens has to change:

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Look at the image and imagine that D increases while f stays the same - it should be clear that the light rays then need to "bend" more. And making optics that refract light rays at large angles without incurring all kinds of distiortions and aberrations is very hard. It requires exotic materials and more lens elements for correction, and of course all of them have to be large (= expensive to make) because, well, it's all about making that opening larger.

And according to the book "Applied Photographic Optics: lenses and optical systems for photography" by Sidney F. Ray, there is a theoretical maximum of f/0.5 beyond which spherical aberrations are unavoidable.

  • and don't forget that more and/or thicker elements means there's less light reaching the film/sensor, and coatings make that even worse. While glass is pretty transparent, it's not 100% transparent. Coatings eat even more into that light budget. So those massively thick and heavy elements, through which light travels at oblique angles, can yield a very dark image. Whether that becomes a problem before abberations become too much to correct for I don't know, would in part of course depend on the materials used. – jwenting Aug 20 '14 at 8:42

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