I tried a couple of techniques tonight, to capture some landscape shoots - HDR and 'Black Card'.
HDR typically uses 3 exposures merged together to create a photo that has extreme highlight and shadow details in one shot. This is impossible to do with just one exposure.
Black card is when you use a piece of non reflective card to block out part of the frame while the camera takes a shot. You then release it when you want to expose the rest of the frame. For example - you compose your shot - a great sun set, with a strip of land in the fore ground. First you meter for the land (say around 10 seconds) and you meter for the sky (say 1 second) You use your piece of card to cover the sky up (so only the strip of land is visible) and set the exposure for the longest setting you need (in this case 10seconds for the land) The shutter opens and then at around the 9second mark you remove the piece of card - allowing the sky to be exposed for the one second it needs. Boom, you have a balanced exposure!
However it isn't that easy - in practice! It took me a lot to get just one shot that I am happy with. A lot of the shots I took ended up with having the edge of the card right across the frame - where I had't matched it correctly with the landscape.
Anyway - I managed to get one shot with the card technique, and one with a 2 shot HDR one.