Headed out to the Kaiserslautern Christmas market with the boys this evening to take in the festivities. It was not so crowded since it was a Monday evening and that made it a little more enjoyable, but it was still cold. Markets and festivals are prime locations for a little low light photography. Modern DSLR’s all seem to have high ISO and can shoot pretty cleanly to at least ISO 1600 or 2000 making it possible to hand hold for shoots you could not possibly have taken just a few years back without a tripod. Add a fast prime lens such as a 35mm f1.8 and set the ISO to 2000 to open up the door for existing light photography. Most people will take their DSLR and set it on auto for everything; this is a bad thing for existing light photography. What happens is the camera meters on the subject, not the background, and the flash pops up and properly exposes the subject, rendering the background way underexposed to the point it goes black. This does not make a very good or interesting photo, however by taking the camera out of auto you can change things dramatically.
Let’s start by discussing a little about aperture and why a fast (wider) one is better. The aperture of your lens regulates the amount of light coming through the lens, much like the valve your garden hose connects to. If you turn the valve just a little then you get a little water. If you select a small aperture, f16 for example, you let in less light than f11. How much less light you ask; half as much. So opening your aperture up 1 stop (f16 to f11) lets in twice as much light. How about opening it up from f16 to f8; 2 stops or 4 times as much light. What if I have a 35mm f1.8 and I open it all the way up from f16 to f1.8? That’s six and a third stops or 12.3 times as much light. Where did that third of a stop come from you ask. Well the next full stop from f2.8 is f2 but your lens goes to f1.8 and that is one third of a stop. But how does this relate to the shutter speed? Shutter and aperture are directly related, as one goes up the other must go down. What this means is if the proper exposure is f8 @ 1/125th then the following would all be the same exposure value and result in a proper exposure:
f22 @ 1/15th
f16 @ 1/30th
f11 @ 1/60th
f8 @ 1/125th
f5.6 @ 1/250th
f4 @ 1/500th
f2.8 @ 1/1000th
Which exposure value you use would depend on the subject and how you envision the final image. If you want to freeze the action use f2.8 @ 1/1000th, or if you want great depth of field (everything in focus) use f22 @ 1/15th. Now lets talk ISO. The control that regulates how sensitive your sensor (digital film) is to light is the ISO. A lower number like 100 is great for situations where there is plenty of light, like outdoors on a sunny day. Higher numbers like 2000 are for low light situations, like your kids dance recital or basketball game. There is one main advantage/disadvantage to ISO and that is noise or what some would call grain. Low ISO’s result in very clean images, i.e. no visible grain (remember the old film days). High ISO’s will have visible noise (grain from the old film days). The good news is that the only people that care about noise are other photographers. Don’t get wrapped up in the noise hype! I have two cameras that I use daily. My primary camera is a Nikon D7100 and it shoots pretty clean at ISO 2500, and is acceptable at ISO 6400. My backup is a Nikon D3200 and it is good at ISO 1600 and acceptable at ISO 3200. Compare these two with my old Pro Nikon D2x that was good up to ISO 800 and horrible at anything above ISO 800!
Now with all the technical stuff out of the way set the camera on ISO 1600, the aperture on the widest setting, and go shoot some existing light images. If all you have is the basic kit lens then you will most likely not have a very wide aperture, probably only f4.5 or f5.6 so you may have to move the ISO up to 3200 or get a faster lens. A good lens for low light photography is the 35mm f1.8, on a crop sensor camera it is essentially a normal 50mm lens which is a close approximation to the human field of view (hence why we call it a normal lens). All major manufacturer’s have one of these and they are much sharper than any zoom lens and are very reasonably priced at around $200.