>>3616438Why do we speak in terms of aperture equivalence for crop-sensor-specific lenses? I.e. lenses that only cover a crop circle; not full frame.
My understanding is that full-frame lenses project a full-frame image out of the back, and using a crop sensor “wastes” some of this image, so the effective aperture number is cropped accordingly. But compared to e.g. an f/2 lens that cover FF, an f/2 lens that projects down to APS-C isn't wasting any light. Aren't lenses that project a smaller circle effectively pre-speed boosted?
Speed boosters reduce the circle projected and reclaim some or all of the lost aperture diameter. Don't APS-C/M43 lenses do this also?
