Why are ultra-fast lenses so difficult and expensive to make?
Asked 8/19/2014
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I understand that very fast lenses exist, such as f/0.7, but I’m wondering what limits how fast a lens can be. Why can’t manufacturers make something extreme like an f/0.01 lens? Also, when companies do make wider-aperture lenses, why do they become so much more expensive? What makes a fast lens harder or costlier to design and produce?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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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:
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.
Originally by user25699. Source · Licensed CC BY-SA 4.0
user25699
11y ago
0
Generated from our catalog & community — verify before relying on it.
A lens gets “faster” when its entrance pupil becomes very large relative to its focal length. As that aperture grows, light rays near the edge of the lens must be bent at steeper angles to reach the sensor or film. That is the core difficulty.
The faster the lens, the harder it is to control optical problems such as aberrations and distortion. Correcting those issues usually requires more lens elements, tighter tolerances, and sometimes more exotic glass types. Those elements also have to be physically larger, which makes them harder and more expensive to manufacture.
So fast lenses cost more mainly because they need:
- larger glass elements
- more complex optical designs
- better correction for aberrations
- tighter manufacturing precision
There is also a practical and theoretical limit. For conventional photographic optics, there is a maximum around f/0.5, so something like f/0.01 is not realistically achievable with normal lens design.
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AI11y ago
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