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Why are lenses with very large apertures so expensive? For example, generally speaking, there is a significant price difference between a f/1.8, f/1.4 and f/1.2 lens of the same focal length. Doesn't the larger aperture lens just have a larger aperture hole to let more light in, and maybe a little more glass. In short, is it actually significantly more expensive for the manufacturers to produce a larger aperture lens, or is the higher price just for the perceived value of the larger aperture?

I hope I've been able to make the question clear.

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  • More general topic, but the accepted answer uses the example of 1.2 vs 1.8, so should answer your question - Why do some lenses cost 10 times as much when the specs are very close? – MikeW♦ Apr 18 '13 at 19:42
  • @MikeW - The accepted answer and the question both compare a f/1.8 lens to a f/1.2 lens. So really the only thing missing is the comparison to f/1.4(which I don't see a necessity to outline). If anything this question is just a bit more broad since it does not cite a specific lens, although I would guess they had the 50mm in mind. – dpollitt Apr 18 '13 at 19:53
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The F number is the ratio between focal length and the the apparent light opening size. this means that you have to make a larger lens for the same focal length. you also get a larger surface that hte light rays enter, and they all have to be focused onto a little dot, smaller than your pixel size to be sharp. If you at the same time have a zoom lens this is even more difficult, especially if you want to keep the same ratio. Even more complexity. So you see how fixed aperture lenses are hard to make. Furthermore, they are also more sought for, especially by professionals - this also adds to the price, and even more value, as they choose to make them dedicated for pros, meaning overall build quality is boosted as well.

So in conclusion, the things that make them costly are:

  • More weight, more material
  • Optically more complex to make, especially zooms
  • and more especially fixed wide aperture zooms
  • cheaper versions are often very soft wide open, especially zooms.
  • the demand is high
  • the wide aperture lenses are also often "made for pros"
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    You answered a question but did not vote it up! I caught you! Why would one do such things? – dpollitt Apr 18 '13 at 19:53
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The optics of a fast lens are more complex because they have to be able to focus light more broadly through a larger opening. When they can focus through a small opening, it is easier to do optically and does not require nearly as many elements or as complex of a design.

Further, each little increase in cost has complicating factors. More elements means more distortion unless higher quality elements are used. Larger and higher quality elements means more weight and more weight means stronger motors to move everything for focusing. Added expense from all of that results in a need to justify the cost and protect the investment, so they have to make the enclosure out of better materials and the mounts and guides for the elements have to be more complex and made of stronger and more valuable materials.

When you combine all the factors and the way they compound each other, you end up with a higher quality, limited product, wanted by many users using a larger quantity of more expensive materials. So yes, the cost premium for them is fairly justified in most cases.

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