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Out of pure curiosity, what is the largest aperture, or lowest f-stop, a commercially available lens has. I have seen the 50mm prime lens from canon with 1.2, but not lower than that. What are the technical problems associated with the size, does it become exponentially more difficult?

marked as duplicate by mattdm, Dan Wolfgang, drfrogsplat, rfusca, AJ Henderson Mar 27 '14 at 13:50

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  • earlier wasn't there a nikon lens that open at 0.98 on 24x36 roll reflex ? There is a Leica 50mm f/0.95 NoctiluxM and a pretty unknow Nokton f/0.95 Voigtlander for 4/3 aps-c – NeronLeVelu Mar 27 '14 at 12:16
  • kipon.com/en/articledetail.asp?id=60 this is only for APS-C (not full frame) sensors and I'm not sure if it's commercially available yet – glaebhoerl Mar 27 '14 at 12:21
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    first, this is not a duplicate because it is asking about the difficulty, not specific to DSLR (for film as well), and even if it was a duplicate, the answer to the other question is different, as it says 1.0 or 1.2 while answers here say 0.7 and 0.95. Maybe there should be a new system in which "duplicate" questions are instead marked, "Updated" – user-2147482637 Mar 28 '14 at 10:53
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    The answers to the other one cover non-DSLR lenses too. (They tend towards "well, it's not for a DSLR, but there is this one...") – mattdm Mar 28 '14 at 17:35
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The SLR Magic Hyper Prime is lower than that at f/0.95, and Leica's Noctilux also offers f/0.95. And then there's the brand new IBELUX 40mm f/0.85.

And if rental counts, you can rent the Zeiss f/0.7 lens made for NASA and famously used by Stanley Kubrick - but only attached to a specific camera. That's often claimed to be the largest practically usable aperture ever made.

What are the technical problems associated with the size,

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

enter image description here

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 because, well, it's all about making that opening larger.

does it become exponentially more difficult?

I don't think the difficulty of lens design can be quantified in a way that would make the expression "exponential" meaningful, but yes, it gets a lot more difficult (which is probably what most people mean when they abuse the term).

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    "I don't think the difficulty of lens design can be quantified in a way that would make the expression 'exponential' meaningful": In terms of time and money, surely, as reflected in the price of the lens (even if that information about the design and manufacturing process itself is not necessarily available publicly)? And given that f/0.5 is supposedly a hard physical limit for glass, I think it would be fair to stipulate that the growth in difficulty is even worse than exponential in some respects, and more like hyperbolic. – glaebhoerl Mar 27 '14 at 13:31

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