While experimenting with the 2.5x extender, I noticed these interesting features within one of the lunar seas. The deep rift or rille, running from northwest to east-southeast through a small crater in the middle of the picture is called Rima Hyginus and the crater is called Hyginus. Rima Hyginus is 220 km long with an average width of 3 km. The crater Hyginus is 11 km wide and 0.8 km deep. It is unusual as it is not of impact origin, but a result of volcanic activity. It lacks the raised outer rim that is typical with impact craters. The rille and crater were probably formed by magma that collected under the surface, forming a 'lava tube' which eventually collapsed, forming Hyginus and the many smaller craters dotted along the rille.

The three conspicuous large craters in the image are; top - Manilus (39 km wide, 3.1 km deep) on the eastern edge of Mare Vaporum, bottom left - Triesnecker (26 km wide, 2.8 km deep) and bottom right - Agrippa (46 km wide, 3.1 km deep).