by damned truths

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Richard, IMHO you mix a little bit things. You need magnification of the lens. And most of the kit lens have magnification 1:5 which is 0.2 and it's enough to see the hair on the image. I find in one old answer here, in StackExchange formula you can use to calculate how big will be in sense of pixels one real object: How do I calculate the distance of an ...


If you have browsed through the technical pages of Pierre Toscani, you probably noticed he is quite knowledgeable when it comes to geometrical optics. Although I cannot ascertain his schematics are correct, I certainly trust him on this, as this is an extremely well researched article. Concerning the maximum possible lens aperture, Toscani says that since ...


There are two hard limits on how fast a lens can be: The first is a thermodynamic limit. If you could make a lens arbitrarily fast, then you could point it to the sun and use it to heat your sensor (not a good idea). If you then get your sensor hotter than the surface of the Sun, you are violating the second law of thermodynamics. This sets a hard limit at ...

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