When mirrorless cameras arrived to challenge DSLRs for their place in every photographer’s bag, the way lenses attached to them had to change. This is because a mirrorless camera, which has no reflex mirror or optical viewfinder, positions the back of the lens much closer to the digital sensor than its film-derived predecessor.
This, in turn, means that the lenses had to change so that they could provide a properly focused image of something closer to the back of them than before. Camera manufacturers took the opportunity to update their lens mounts, which in many cases were decades old, so that they could add new features.
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