Due to diffraction at the image plane, all optical systems act as low pass filters with a finite ability to resolve detail.
If it were not for the effects of diffraction, a 2" aperture telescope could theoretically be used to read newspapers on a planet circling Alpha Centauri, over four light-years distant.
The spatial cutoff frequency for a perfectly corrected incoherent optical system is given by where
So, the telescope's optical resolution is about twice that of high-resolution film, and a crisp, sharp picture would result (provided focus is perfect and atmospheric turbulence is at a minimum).
This formula gives the best-case resolution performance and is valid only for perfect optical systems.