Autofocus is so good on modern cameras that most photographers use it all the time. It seemingly never lets you down. But, let’s say it’s nighttime and you are going to do some shooting. You find a good spot. You set up your tripod. You go to focus your camera using the autofocus. You can feel the camera’s focus ring twisting back and forth, trying to focus. But it never gets there. The camera keeps hunting for a focus spot but never finds one.
Uh-oh. What are you going to do now?
Actually, this problem doesn’t arise only at night. Your camera will typically have trouble focusing in any really dark scene. So here are some tips for dealing with that situation and focusing your camera when it is dark
1. Aim for the bright spot
Sometimes you can still use your autofocus. Even though it is dark, most night scenes will have a bright spot or two. They might be streetlights, or a lit-up building, or even the moon. That bright spot can be used to set your autofocus.
To do so, find a bright spot that is reasonably close to your desired plane of focus (i.e., the same distance away as your focal point). Autofocusing on that point should take care of your problem. Just focus on that bright spot in a normal fashion and your camera is now focused on something the same distance away as your subject. You should then be able to take your picture with proper focus.
2. Focus on the edge
Most cameras focus using something called contrast detection. That means the camera will have the best chance at finding something to focus on if you aim at the area of high contrast between something bright and the dark background. So don’t aim your focus point at the middle of the bright spot in your frame. Rather, focus on the edge of the bright point. The camera will use the contrast between the very light and the very dark tones to focus.
3. Use a flashlight
If you are attempting to autofocus on a relatively close subject, you can use a flashlight to assist with the focus. This is one of the many reasons to keep a flashlight in your camera bag.
To do that, shine your flashlight on your subject. That will lighten it up enough for the camera to focus on it. Set your focus, then you can turn off the flashlight and take your shot.
4. Recompose after focusing
Assume you now have your focus set using the methods set forth above. But to get that focus, you had to move your camera away from your desired composition to focus on the edge of a bright spot. Move your camera back to your desired composition to get the shot. Don’t refocus as you do so though – just move the camera and take the shot with the focus you’ve already set. (You will need to either hold the shutter button part way down, use focus lock, or focus and then turn off the AF so it doesn’t attempt to refocus once you have recomposed – or see #5 below.)
5. Use back-button focus
It is times like this, when you want to take a shot with out refocusing, that back-button focus really pays dividends. If your camera allows it, go into the menu and set up your focus so that it is not triggered when you press the shutter button halfway down, but rather is triggered when you press a button on the back of your camera. That way since your focus is not set with the shutter button, when you take the picture by pressing it there is no chance that your camera refocuses.
6. Manually focus using the lens scale
If there is nothing for you to use to set your autofocus, you might have to use the dreaded manual focus. But don’t worry, it is not difficult. In the dark, it is often easier to focus manually than hunt for something to use for autofocus.
Higher-end lenses make it easier to manually focus. In a high-end lens there should be a scale on the front that tells you the distance (in both feet and meters) at which you are focused. Use that to set the focus.
You might need a flashlight to see the scale. This is yet another reason to keep a flashlight in your camera bag.
7. Manually focus by guestimating
If you cannot find a point to focus on, and your lens does not have a distance scale, all is not lost. You can guestimate and get it right in a lot of cases.
To do so, make sure you are shooting with a high aperture value (small opening, large f-number). That will create a wide depth of field to give you some wiggle room in your focus. Specifically, the wide aperture will make a wider range of things acceptably sharp in your frame.
In addition, be sure you are shooting with a wide angle lens. This is not the time to try anything telephoto. The wider angle of view creates a more forgiving environment for your focus.
With a wide aperture and the wide angle of view, you have a broader latitude in your focusing. Now manually focus your camera. If you are shooting a broad scene that extends to infinity, set the manual focus just shy of infinity. The latitude you built-in will make things acceptably sharp all the way to infinity and a certain distance in front of your focus point as well. That will give you the best chance of having the whole scene in focus.
8. Use Live View
If you can see anything on your camera’s LCD using Live View, then you can use that to manually focus. This is frequently better because you can zoom in on your subject and clearly see if you have nailed the focus. Try using this whenever possible, as it allows a degree of control over focus that is not otherwise possible.
9. Remember you get a do-over
One of the beautiful things about digital photography is that shooting is free. Unless your scene is moving in front of you, you get a free do-over. Use it liberally. Take a shot, look at it on the LCD, and if the focus isn’t right, just do it again. If your camera allows it, go ahead and zoom in on the preview to clearly see the detail and whether or not you have nailed the focus.
These tips will help you set your focus at night or when you are in a very dark scene. In fact, some of these tips will also help in broad daylight when the camera thinks it is dark because you are using a 10-stop neutral density filter. Try them when your autofocus is hunting but not finding the focus. You should be able to nail the focus in almost any situation