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sort of true ,but at some point physics takes a hold ,and front elements have to be a certain size to gather the light ,i know being a m43 shooters which is half the size sensor of your apsc sensor ,and that a 600mm lens will still be as big and heavy as your full frame 600mm lens ,which is basically a 95mm front element for f6.3 for example so regardless of the projected light needed on the other end the lens to the sensor. Which on m43 is 4 times smaller and aps-c which is 2x smaller  than a 35mm sized sensor ,but on the other end of the scale things can be a lot smaller/lighter  travel zooms for example  etc where front front optics do not need to reach a criteria on crop sensors  .On this note you still pay a premium for compact and small on crop sensor lenses ,and you can throw equivalence in to equation also so ff is 1 stop different to apsc ,so a 50mm f1,4 lens on ff  to match it on apsc you need a 35mm f1.0 ,for field of view .dof and light gathering due to the crop sensor .