>>3307033Focal length makes a lot more sense with something like a telescope, where it is literally the distance the light travels within the telescope, from the objective to the eyepiece. You can measure a telescope with a tape measure and easily determine its focal length.
With camera lens designs, things tend to get more tricky because they have elements that manipulate focal length built right into the lens. Without such teleconverter-like elements and speed booster-like elements, it would otherwise be impossible for lenses like the Pentax DA 21mm f/3.2 and 70mm f/2.4 pancakes to be the same physical length and size while one has over twice the focal length. That's why not all lenses produce sharp images when you further add on an external teleconverter or speed booster. Sometimes, the result is fine, other times, the result is just not sharp.
>>3307038>A crop sensor can't take advantage of full frame lens. Since it's roughly half the surface area.>50% of the outermost area is cropped away, while the 50% area closest to center is captured by the crop sensor.>That's why it's called crop sensor.>>What?>Did you actually believe your Crop sensor captured everything that goes through a full frame lens?You are retarded and I'm quoting your retardation in full just in case you decide to delete it out of shame and embarrassment.
A speed booster is literally a piece of glass you attach to a lens that changes the actual, not equivalent, focal length and maximum f-stop. It has nothing to do with sensor size.
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