Comment by snowwrestler

The amount of total light is the same, but the smaller the points of focus, the easier it is to distinguish image elements from each other because each point overlaps less with its neighbors.

Here’s a metaphor. Let’s say you have 10 glasses, with 10 different amounts of water in them. When you hit them with a spoon, each glass makes a different musical note: 10 different notes.

If you pour the water from each glass individually into 10 new glasses, you preserve those 10 notes.

If you combine every two glasses into one, now you have 5 glasses, and only 5 notes. It’s the same total amount of water but you lost information.