I have been looking at different font options and i am slightly confused by some of the terms. Can any body tell me where the "Medium" and "Semi-Bold" fonts fall in relation to the terms: Display, Subhead, Body/Text, Caption. I have read the following article: Adobe - Fonts : Type topics: Optical Size but still don't know where they fit in.
Optical Size terms are orthogonal to Weight terms, and thus have no relationship. Think of Optical Size as a different axis, similarly to how the Width axis (Compressed, Condensed, etc) is independent from the Weight axis.
Thank you Miguel.
So, what would 'Medium' and 'Semi bold conventionally be used for? I'm just trying to figure out if i need to buy them or not.
That's up to you. There's no prescription to when to use Medium, Semibold, or Bold. Use Medium or Semibold wherever Bold looks too heavy, I guess.