I'm a very conceptual person, and I've been reading about exponential and logarithmic growth but don't fully have the kind of conceptual grasp on the two and how they differ that I'd like, so I"m curious: What is the difference between exponential growth and logarithmic growth and what causes this difference? Also, according to Wikipedia: "In mathematics, the exponential function is the function ex, where e is the number (approximately 2.718281828) such that the function ex is its own derivative." What does it actually mean for ex to be its own derivative? Does it mean that ex always equals e no matter what x is... I don't think so? And one more related question: in photography, 18% reflectance (18% gray) is said to be perceptually equivalent to 50% of the brightness of 100% reflectance (full white) because our visual system's response to brightness is logarithmic. But my question is what is the math behind how 18% is an equal number of steps between black and white? Thank you so much!