The title of this post is a somewhat rhetorical question, because whether or not you’ll be able to tell the difference largely depends on what you’re shooting, the lens you’re using, the level of tech in the sensor and how the final image is going to be displayed. But there are definitely some differences between sensors at different sizes.
In this video, The Slanted lens takes a look at four cameras with different sensor sizes in various conditions to see how they stack up against each other. Interestingly, they don’t just pixel peep on the computer screen, either. They also make 24″ prints to see if you can really spot the difference in the real world.