Condenser microphones are commonly found in recording studios but not often on stages because of the different way in which they pick up sound. Condenser microphones use a diaphragm, just as the dynamic microphone does, but instead of sitting in front of a wrap of coil (the voice coil), the diaphragm sits in front of a stationary plate of metal called the back plate. The diaphragm in a condenser microphone is always made of thin metal or metal-coated plastic. Both the diaphragm and the back plate have polarized voltage applied to them. As the diaphragm moves back and forth in relation to the stationary back plate, a very small current is produced, which is your signal.
Condenser microphones are often classified by the diameter of their diaphragms. Obviously, large-diaphragm microphones are larger in size than small-diaphragm microphones. Large diaphragms are more sensitive to low level sounds, than small diaphragms. Small diaphragms can handle louder overall sounds, however. Condenser microphones can range from $100 to many thousands of dollars. The good news is that you don't have to spend a lot to get a good-sounding one.
Another type of microphone is the ribbon condenser. Instead of using a traditional diaphragm as the dynamic and condenser microphones do, a ribbon condenser uses a very thin and flexible ribbon to pick up the sound. Ribbons are very fragile and can be damaged with mishandling. Because of their high price and fragility, they are much less common in home studios. Recently, budget-priced ribbon condensers started to appear on the market. Even the budget ribbon microphones are much more expensive than other budget microphones, but they have a unique character to their sound that is worth investigating.
Condenser microphones are used for everything that dynamic microphones can't do. Condensers are more delicate and more expensive than their counterpart dynamic microphones. What condensers have going for them is that they re-create the sounds they are given very accurately. Condensers usually have flat and wide frequency response, hear all frequencies, and tend not to boost or lower any particular frequency. This is why condensers are the microphones of choice for acoustic instruments such as piano, winds, strings (including guitar and bass), drum overheads, and vocals.
As for polar patterns, some condensers can utilize all polar patterns. This makes them ideal when you have to pick up a whole room with one microphone using an omnidirectional polar pattern. Couple this with the fact that some condenser microphones can switch polar patterns, and you've got one flexible microphone. Most condenser microphones can't handle super-high sound-pressure level, so don't replace all your dynamic microphones with condensers. On certain condenser microphones, you might get a pad switch that lowers the microphone's output by 10dB or more in order to better handle louder sounds.
Condenser microphones do a much better job than others at capturing a true spectrum of sound, from its lowest to its highest pitch. However, condenser microphones are more sensitive and delicate, and typically can't handle high sound pressure. You can actually fry a good condenser with high SPL if you're not careful!
Repeated exposure to high SPL can cause permanent hearing damage. Don't crank the sound in your studio and be especially careful with headphone volume. You get only one set of ears.