Forum: Pentax SLR Lens Discussion
12-08-2017, 04:32 AM
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I think a better example of what OP is asking would be lenses like FA 50mm f1.4 and Sigma 50mm f1.4 art (or the new DFA* 50mm f1.4, by the looks of it). Both are 50mm, both are f1.4. But one is much bigger, which makes a lot of people wonder how they can still have the same focal length and aperture. In this case, its not just filter threads, but actual amount of glass
The answer is that we are not dealing with simple lenses, but very complex ones with many elements, special materials.
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