1. The problem statement, all variables and given/known data This is not really a homework problem but I wanted to figure out how to derive the equation for a strained eye which is $$ M= (N/f) $$ where N is the object distance from the normal near point, and f is the focal length of a magnifying glass. But then, this is for a relaxed eye, why is it $$ M= (1+(N/g))$$ for a strained eye? 2. Relevant equations I know that the equation for angular magnification is $$M=(θ'/θ)$$ and I also know that this is for when you use a simple magnifying lens. (I tried inserting Greek letters using latex but doesn't seem to work? I wrote /theta, isn't that how you do it?) 3. The attempt at a solution I know that for a strained eye, is like when you squint the eye, which would reduce the light rays that enter your eye, but how does that change the focal point, and how does that lead to a plus one in magnification?