The naïve optical instrument will be diffraction limited. The resolving power of a lens, basically how "sharp" the resulting image will be, goes down as you dec

The naïve optical instrument will be diffraction limited. The resolving power of a lens, basically how "sharp" the resulting image will be, goes down as you decrease the size of the aperture relative to the focal length (that is, as the f-stop number goes up). A telescope that could zoom into an exoplanet would have an f value of a kajillion or so.