Strehl ratio

Okay kiddo, so imagine you have this big glass window and you want to see the world outside it as clearly as possible. But sometimes the window is dirty or blurry and things outside look fuzzy. The strehl ratio is sort of like a measure of how clear the window is.

Now, when we look through telescopes or cameras, they also have something like a window which is called the lens. And just like the window, the lens can also get dirty or blurry, which makes things look fuzzy.

The strehl ratio helps us measure how much of the fuzziness we can remove, so we can see things as clearly as possible through the lens. It's a number that tells us how well the lens is working, kind of like a grade in school.

A high strehl ratio means that the lens is doing a good job of making things clear and sharp. A low strehl ratio means the lens is not doing a very good job and things might look fuzzy or blurry.

So, if we want to take really good pictures of planets or stars, we have to make sure the lens is clean and working well, so the strehl ratio is high and we can see things as clearly as possible. And that's what the strehl ratio is all about!