As this is the 'most advanced' part of this tutorial I will not get too much into technical stuff. I will assume you all know how to change the exposure and how to make sure you have enough light for whatever you are planning.
The key here, is planning. Although it is easy to just look at the screen and see what came out (or even use a bracket set - as explained below), when you start to know what you are looking for in an image is when these over/under settings really become part of the creative process.
If you still need some help getting images sharp in tough lighting conditions then take a look at the previous post in the series.
If aperture and shutter speed are unfamiliar terms, consider going over the first part.
Most SLR's and some point and shoots allow you to take three or five shots where one exposure is at EV0 (at the "correct exposure") and the rest some ways above and some ways below that exposure value. This is for when you don't know which exposure will look best. It is also useful for HDR compositions but I don't want to get into that...
|example bracketing set at +-one|
So, what I am saying is that sometimes the camera doesn't know what is the best exposure. Sometimes we just have to try all sorts of exposure values, either by bracketing or by using the +/- key.
I don't want to go into too many details. Mostly I just want to show examples. Some of the pictures are presented as they left the camera, to emphasize the effects of the exposure bias. Keep in mind these pictures still require some additional tweaking for brightness, as well as contrast and sharpening treatments.
-Bright Background: One possible reason to reach for the + button is because a camera sensor may be confused by a lot of bright areas in the frame. If I am photographing a person on a white background the camera may consider the overall image to be properly exposed, with the person's face too dark.
|The camera sees the 'right exposure" (18% grey) but Darth is lost in lost in the dark side|
|Giving a +1 correction washes out the wall a bit but allows more detail for Darth.|
-Silhouette: Another, similar example is when a person comes out as a silhouette, usually for sunset shots. We could overexpose or measure light using the spot or central weighed meter, but often the best way is to put +2 in the EV or just go to M mode and play with it.
|The sunset is properly exposed (I would under expose it even more) but the guy is a bit too dark|
|EV +1. Now the sky is blown out but at least the subject is well lit.|
-Blown BG: An extreme case of the white wall is when we want to really get the background to blow out, or just want to make a portrait intentionally blown out. Obviously this is not 'properly exposed'. The camera will yell at you for going to EV+2.3 but who cares, if it looks good?
|In this example I took Darth to EV+2 to deliberately blow out the wall. It also helps with his complexion|
-Drama: The main reason to under exposed (besides not having enough light), is to create dramatic images. It is said that a photographer should keep details in the shadows and not underexpose them too much. Then again, being creative sometimes means breaking some rules. Feel free to try under exposing between EV-0.7 and -2.
This works very badly for images that are pretty uniformly lit, but if a small part of the image is brighter than the rest, properly exposing that part will leave the overall image very much 'underexposed'. But the result is a well lit section with a lot of dramatic shadows around it.
I like to add contrast and black clipping in lightroom when I take these pictures. I don't mind the shadow parts to go into total black, as long as there are no important details inside. Most details are distracting anyway. I don't mind large, pitch black pools in my images.
-Sunsets: As we saw before, a sunset silhouette can be taken with the person either blacked out or well lit with a blown out background. If we do want to see the person (or any other foreground detail) we could use a flash* to add light to the person. Since the flash is measured separately from the regular exposure, we can underexpose the background and light the person in a normal lighting. This gives a nice, dramatic sunset with the foreground lit well.
|This was made with an off camera flash but the idea is pretty much the same.|
*Yes, you can do this with a built in flash. It is almost the only reason to ever use it. If you have an external flash it will work so much better for this. If you do want to use this trick with the built in flash, try standing as close as you can, and choose the fastest shutter speed you can.
(technical: I don't want to go into flash uses because it is a world on its own, but the flash can't sync faster than around 1/200sec - depending on camera - and after you set that in you will need to close the shutter or drop down ISO to get the sky darker. Both these things make the flash work harder and harder. Since it is only the built in flash it really helps if you stand close so you don't lose what little light it is throwing.)
-Light Beams: Sometimes we see these interesting light rays and want to capture them the way we see them. Often the contrast between the light rays and the darker background is what lets us really see the light. Our camera, however, will probably want to expose the dark background as 'properly exposed' background, ignoring the little light it gets from these light rays.
|Gosainkund, Nepal, May 2011. f/2.8 ISO 400 @ 1/160sec. Underexposed by about 1.3 stops.|
Try these with several different exposures. It's a tricky situation that requires some trial and error. But be quick about it, these light rays usually move and vanish really fast.
-Light Painting: Another useful thing to do at night is to take pictures of light emitting objects while they move. This is called light painting, and it is best done on a tripod.
|5 second exposure in a dark room|
After you got the tripod setup and got the light trail going, try to use your flash to freeze motion at the end of the frame (use SLOW setting to allow long exposure with flash and REAR setting to have the flash fire at the end).
If you don't have an open space behind the subject this will be awful, as the whole point of light painting is to have a dark background. If the wall behind the subject is far away enough the flash will not make it too bright.
|f/5 with a 1 second exposure @ ISO 200. The light trails have enough time to form and the flash freezes motion.|
This above image is from the night catalog I did last year.
-Moving water like rivers and waterfalls are sometimes more exciting when you expose them using a long exposure. Make sure you use a tripod.
|This was taken with the Minolta Z6 which had a stabilizer, so I didn't need a tripod for 1/8th of a second|
-ND filters: Sometimes there is so much light that even if you close the shutter down to f/22 and lower ISO to the minimum, getting a long exposure still puts too much light in. Contrary to the situation where you don't have enough light, when you have too much light you can use an ND (neutral density) filter that just reduces exposure.
These filters are useful mostly when doing these long exposures in daylight (otherwise you can just close the aperture a bit). If you are taking your tripod along for long exposures during the day, such a filter will be very useful.
-Motion: Another, similar situation is when we want some moving objects to have an appearance of motion. A longer shutter speed smears moving objects, and conveys a feeling of motion. If you can follow a moving object during the exposure it will be sharp and the background will be blurred. Try this at different speeds, and if you get too much light (maybe you want a large aperture to get soft backgrounds) use an ND filter here as well. If you are doing very long exposures (more than 1/5sec) a tripod might also be useful.
|f/22 @ 1/8 second using ISO100 (using an ND8)|
-lightning/fireworks/star trails: When trying to capture any of these things, a long exposure on a tripod is necessary. Ignore the light meter and shoot in M mode. Leave the shutter open for 30sec, and try to find an aperture that doesn't blow out the picture but still leaves enough light for the subject. This will require some trial and error since you don't know in advance how bright your subject will be when it appears.
If you are doing this with some earthly objects in the frame (mountains or buildings) make sure they are exposed properly (or close enough too) so there are details left on them but they don't burn out your image.
|One image out of a few hundreds I took with a locked remote that night.|
Depending on what you are photographing, finding a balance between the fireworks and the buildings may be hard. For example: star trails are much fainter than street lights and buildings, so you can't see too much star trails without blowing out the foreground.
Exposure part I: Proper Exposure (aperture, shutter speed, ISO and all that goes with them...)
Exposure part II: Know your Limits (how to choose the right exposure under tough lighting conditions)