Twilight is a magical time.
Just because the Sun is down, doesn't mean you should put away your camera.
When the Sun sets, a different looking world exists for photographers. Colors don't appear the way they do in daylight.
Instead, colors display based on your camera's white balance setting and how that setting matches the various light sources in your scene.
Backgrounds become less distracting.
Street lights and lit building interiors give you outlines and shapes of various colors.
Chances are not everything in your scene is lit. So what you see in your viewfinder is very close to what you'll get if you expose carefully and properly.
People in your scene don't matter as much unless you want them to. Passers-by don't register in your image.
Even if they do, they are a blur unless you "freeze them" with a flash.
Cars show up as trails of red and amber lights. Skies take the color or aura of the city's lights especially if there are low lying clouds to reflect it.
Compared to other subjects, night photography doesn't require a whole lot of equipment. The following are necessities:
A steady tripod
a cable release to trip the shutter. Most people can get by using the self-timer. The key is to not shake the camera when you trip the shutter.
a flashlight to illuminate the knobs and dials of your camera.
optional-- a portable flash with lots of batteries
You pretty much will get what you see in your viewfinder.
You don't have to worry about trying to light anything except when you want to include a person in the picture. But I'll discuss that later.
The various elements in your picture lights itself freeing you to just concentrate on your composition and exposure.
Fountains tend to have spots and colored lights on them, christmas trees are never displayed in public without multicolored lights and beautiful majestic architecture in most civic centers are usually brightly lit up showcasing a city's pride.
Here's how to set up:
Change the ISO on your camera to 1600 or whatever the maximum number is.
If you have a digital SLR, attach your longest focal length lens on your camera and take a light reading. The idea here is to use the narrower field of view so that your lightmeter can give you a more accurate light reading. If you have spot meter reading mode on your camera, that will give you a similar result.
Take note of the exposure reading you get in step 2.
Calculate that exposure reading for ISO 200
Switch lenses to a wide angle or even a more "normal" focal length lens and compose your shot. Mount your camera to the tripod.
Tighten all the axes on your tripod head so that your camera doesn't move in during the exposure.
Finally, set the camera to the self-timer mode. Some cameras give you a choice of 2 seconds or 10 seconds. The whole idea is, you don't want to jostle the camera when you press down on the shutter. Let the camera settle on its own and 2 seconds ought to be enough for that.
Calculating Exposure
Making your camera's CCD or CMOS more sensitive to light makes it easier for you to get a light reading.
If you leave your camera's ISO at 100 or even 200, your meter might not register a reading especially if the scene is something lit only by moonlight.
Remember that there are always 3 components to exposure: ISO, aperture and shutter speed. For the sake of our discussion, let's say when you pointed your camera in step 2 at the scene, your meter recommends 1/15 sec at f 2.8 ISO 1600.
If you haven't read this yet, then just take my word on this. High ISO settings yield images that are extremely noisy. That's the equivalent of grain in the analog or film world.
So what we'll do next is figure out equivalent exposure at say ISO 200. How did I arrive at a shutter speed of 1/2 second for an aperture of f2.8 when I switched the ISO from 1600 to 200?
ISO 200 is 3 f-stops less sensitive than ISO 1600. There are 2 ways for me to do achieve equivalent exposure. Let's examine the first method which entails leaving the aperture the same at f 2.8 and only changing the shutter speed.
That means I'm only increasing the time the shutter stays open, allowing in more light by the same 3 f-stop factor.
So I'll need to set the shutter speed from 1/15>1/8>1/4>1/2 sec (counting from 1/15 sec > 1/8 sec> 1/4 sec>1/2 sec = 3 stops)
Now that you have your exposure for an aperture of f 2.8, let's say your subject has some depth and you want to be sure more of it is in focus. You can figure your exposure by changing the just the aperture, leaving your ISO the same at 200.
Let's say you decide you want make your picture at f11 giving you more depth-of-field. You again have to increase the time the shutter stays open in the same ratio or f-stop to get the equivalent exposure. F11 lets in 4 stops or 4 times less light than F 2.8.
So you'll need to set a shutter speed of 4 whole seconds. (counting the aperture settings from f2.8 > f 4> f 5.6 sec>f 8.0>f 11 = 4 stops)
(counting the shutter speed settings from 1/2 sec>1 sec> 2 sec> 4 sec = 4 stops.)
The second alternative to achieve equivalent exposure, opening the aperture to let in more light, is not always practical because I would be restricted to using my "fastest" lens, a 50 mm f1.4.
Even that lens has physical limits--it's widest aperture is f 1.4. The resulting image would still be underexposed by 1 stop. I would need to buy a 50 mm f 1.2 lens. Have you priced one of these? Canon makes one for about $1500.
If you have a tripod, you have the luxury of dropping your shutter speed without worrying about camera shake. That is often your best option because you really don't want to be making pictures the whole time at your widest aperture whether it is f 1.4 or f 2.8.
At those apertures, focus is critical since the depth-of-field is very shallow. If you happen to set up on a pedestrian bridge and people are working on it as you are making the exposure, then you might have to wait for a lull in foot traffic.
