In the case of an altazimuth telescope, the Cassegrain focus and Nasmyth focus have different characteristics. The greatest difference lies in the movement of the focus when positioning the telescope.

The Cassegrain focus moves up and down in accordance with the inclination of the telescope, but the Nasmyth focus is always kept level at a certain height, thanks to the third mirror. In terms of accuracy and limiting magnitude, however, the Cassegrain focus is more advantageous, because light is not reflected off a third mirror.

Observation instruments used for taking ultraprecise measurements are usually attached to the Cassegrain focus. On the other hand, the Nasmyth focus is good for large and heavy observation instruments that require a sturdy mount, because focal height does not change and because the instrument can be kept in the same position.

The observation instruments on NAYUTA have been selected based on careful consideration of such focal properties.