Autofocus and Night Photography
Recently a reader, Jeremy, left a comment one of my photos about focusing in low light situations.
“Yes, actually, I do have a question: How do you focus? In my experiences with night/low light photography, the autofocus tends to hunt and never converge. (No matter if I am using a tripod or not. Actually, the tripod isn’t even the issue, given the low contrast of the scene itself.)”
Which is a good point. In the example that Jeremy was talking about with night blur photography autofocus isn’t so much of a problem because there is enough light on the ride or whatever you are shooting to lock in and set the focus there.
So let’s talk about autofocus at night. The first situation you have is where you are shooting something with plenty of light. This can be a cityscape at night, an amusement park ride, the moon, a lit bridge, etc. Well here usually the first part of autofocus isn’t a problem. You simply point your camera at where you want and it locks right in.
So when you have enough light, what you want to do is find your focal spot and press the shutter button halfway down. This will position the lens in focus with where you want it to be. Then before you fire your shot either with your finger, your cable release or your timer release, you set the lens to manual focus. The lens will remember the focus point and you can shoot there. If you don’t lock the focus in manual mode first, often times the autofocus will start hunting around again and you’ll miss your originally positioned focal point.
The next situation comes into play when you *don’t* even have enough light to get autofocus to lock in in the first place. I’ve found some lenses autofocus better in the dark than others. For instance. My Canon 24mm f/1.4 does a far better job in the dark than my Canon 50mm f/1.2 which does a crappy job in my opinon.
But anyways, sometimes you just can’t get the autofocus to lock in period. And this is where if what you are shooting is close enough a flashlight comes in. With this technique you simply shine a flashlight on whatever you want to focus on and then push your shutter halfway down locking in on that focal spot. The flashlight provides enough light to lock in the focus and then you turn your flashlight off, switch the camera to manual focus (locking in the autofocus setting you just set) and shoot your shot. This technique is helpful for getting things like night silhouettes especially crisp.
The other benefit of bringing a flashlight with you when you are shooting at night is that you you can use it to add a tad more light to a subject you are shooting in the foreground if need be, or you can use it to actually do some light painting in super dark locations.
Recently I was shooting the bunkers out in the Marin Headlands at night (the shot above as example). It was way too dark to actually shoot in the bunkers, but by painting with a flashlight (literally shining the flashlight over the subject with strokes while my shutter was open for long exposure shots), I was able to get my subject with an interesting lighting effect from the light painting.
Night shooting is one of my favorite ways to shoot and a flashlight definitely always comes with for those shoots. By the way if you want to check out some work by some great Bay Area night photographers check out these pages by Andy Frazer, Troy Paiva and Joe Reifer.