I'm new to the world of macro so do bear with me! I shoot pictures of fish through aquariums, so normally this means the lens is always perpendicular to the glass surface to avoid blurring.
However the cost of a perpendicularly positioned lens is that, if the fish is not presenting itself along its lateral aspect, I can't tilt. This leads to some unflattering head-only shots.
So I'm trying to find the highest aperture for my camera body, but want to avoid diffraction limiting the photo and adding more blur than I need.