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Why a bigger diameter lens can gather more light. Consider, on a dark night, you can see the glow of a burning match off in the distance. Your friends standing near you can also see this distant glow. Translated, the light from the match radiates outward in all directions. Your eyes only receive a fraction of its radiated light. For your friends to see its ...


3

Can someone please explain how having a large diameter makes it a premium lens. The point is also indirectly linked - manufacturers usually create slower entry level lenses with budget specs, like Canon's 50mm 1.8 - dirt cheap, good image quality, but feels like a toy. It has a cheap plastic body, that's nowhere near what they use for the good lenses. Fast ...


4

As we calculate FStop as FocalLength/diameter this implies that this lens must be having huge diameter to achieve 1.4 Fstop. Larger than a lot of lenses, but not "huge" in human terms - 85mm / 1.4 = 60mm - or about the size of the palm of your hand. But this isn't a small lens - it weighs the best part of a kilo. Can someone please explain how ...


1

I believe I now see the confusion (sorry, slow on the uptake). Most lens and imaging diagrams do indeed give the impression that all the light comes to a point at the focus point, it's even in the name. However that's not what is actually happening. The smallest point of light is actually an image, not a point. The focal length of a lens refers to the fixed ...


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