Activity
In adsorption chromatography, this is the relative strength of the surface of the packing. For silica gel, the more exposed the silanol groups, the more active the surface. Activity can be controlled by adding water or another polar modifier, which is hydrogen bonded to the active sites, thereby reducing the surface activity.
I really agree that good photography is often more about noticing light and timing than having the newest gear. I’ve found that slowing down for a few minutes and watching how shadows move can turn an ordinary scene into a much stronger image.