4 Lensing Phenomena

In this section, we describe different groups of gravitational lens observations. The subdivision is pragmatic rather than entirely logical. It is done partly by lensed object, or by lensing object, or by lensing strength. The ordering roughly reflects the chronological appearance of different sub-disciplines to lensing. The following sections are on:

• Multiply-imaged quasars.
• Quasar microlensing.
• Einstein rings.
• Giant luminous arcs and arclets.
• Weak lensing / Statistical lensing.
• Cosmological aspects of (strong) lensing.
• Galactic microlensing.

Comprehensive reviews could be written on each separate subject. Hence the treatment here can be only very cursory.