The INT has a 2.54 metre diameter primary mirror with a focal ratio of f/2.94. It uses a polar-disc/fork type of equatorial mount. Two focal stations are in use, the corrected f/3.29 prime, and the f/15 Cassegrain. Prime focus is used entirely for imaging, and Cassegrain primarily for low- and intermediate-dispersion spectroscopy. Both focii are equipped with instrument rotators and autoguiders, and the Cassegrain A & G box contains a TV camera for field and slit viewing.
The Cassegrain focus has an unvignetted field of view of 20 arcmin diameter, and the corrected prime focus a field of 40 arcmin diameter.