ONSET is suggested to explore the solar eruption in the solar atmosphere layer between the chromosphere and corona of the solar atmosphere. It is composed of four tubes：

1）：f 275mm vacuum tube with a 1083nm/0.05nm Lyot filter。

2）：f 275mm vacuum tube with a 656.3nm/0.025nm Lyot filter。

3）：f 200mm vacuum tube working on 425nm and 360nm by use of corresponding interference filter of 1.5nm FWHI.

4）：f 140mm guiding tube。

　  All tubes are placed in a compact equatorial mounting with very nice appearance。

　  ONSET is working on two observing modes: Whole and local region with high optical resolution。

　  ONSET will be installed in a site near by a big Fu-Xian Lake with excellent daytime seeing。