[10cm Coronagraph]
The 10cm-aperture coronagraph was built in 1950. Coronal green-line (5303 Angstrom) emission has been observed continuously since then, by using a direct-vision spectroscope. The number of observing days per year is roughly 100, and the data are reported in IAU Quarterly Bulletin on Solar Activity.

From 1997 to 1998 a major improvement in the optical system was made. In our new system (NOGIS; Norikura Green-line Imaging System), a 5303 Angstrom Lyot filter can provide two-dimensional maps of green line intensities and Doppler shifts. Together with a cooled CCD camera, very high sensitivity observations of the solar corona are now possible.

[New 10cm Coronagraph]
The 10cm-aperture 'new' coronagraph was built in 1990 and mounted next to the original 10cm coronagraph. With a CCD camera and an image processing unit, this instrument can perform high sensitivity photometric measurements of the solar corona. The observing wavelengths can be selected by four filters. In an observation of the so-called coronal condensation in continuum light combined with the X-ray observation of Yohkoh, we were able to detect a plasma whose temperature was about 20 million K.