Photo Tips Podcast - Podcast:How to Focus in Low Light #15
How to Focus in Low Light
No matter which latest and greatest camera you have, if you enjoy night photography or shooting in low light you are going to have focusing problems at some point. At the moment there’s not a single camera available for consumer use that can rival that of the human eye under extreme low light. So until that happens you need some strategies for dealing with low light because at some point your autofocus system is going to fail on you.
In order to see, we need a presence of at least some light, otherwise everything will be pitch black. I know that’s obvious but on the other hand it also needs to be understood that we also see because of a presence of darkness. Without shadows or darkness everything would be white. I learned this the hard way when I went skiing in Aspen many years ago. Until then I had only skied the mountains of California where there are some great mountains but we never had something called bowl skiing available. For me the idea of skiing down a huge open bowl of snow was like a dream. Except, I didn’t realize there was a small problem. I couldn’t see any of the moguls in the snow. When you have a gigantic area of snow shaped like a bowl, the light is not just coming down from the sun in one direction revealing bumps in the snow by leaving shadows on one side, the light is bouncing all around due to all the snow in the concave shape of the hillside, thereby making the surface seem completely flat. As a result I could not anticipate the moguls with my eyes and basically fell on every bump in my path until I got out of the bowl. That was the moment I learned that sight requires both the presence and the absence of light.
This is important to understand in low light focus because you can not take a photo without some semblance of light. But if there is not enough light for the camera to find focus, the simplest and easiest solution is to add light. If the subject is close enough, use a flash light or throw a strobe on it. Before anyone gets excited, I’m not saying to leave it on for your final shot, I’m just saying use it to help your camera find focus. Most cameras and flash systems now have a focus assist mechanism which will help the camera find focus in low light and the one on the flash is usually better. If the camera is able to find focus after pressing the shutter button halfway, turn your focus to manual focus. This way the lens won’t try to refocus the next time you press the shutter button or accidentally press the back button focus button. Once the camera finds focus be sure to turn off your flash. Btw, this whole discussion is about shooting stationary objects and while using a tripod. This won't work very well for shooting moving objects. If your subject is too far for a flash or a flashlight, you’ll need to look for an area on your main subject where you would find a hard edge on your subject that falls against something lighter. For instance, let’s say you are photographing a large cactus against the moon, but your subject is the cactus and not the moon, because the moon would be too obvious and too easy. The problem is that the moon is back lighting the cactus and it’s night time, as a result the camera can’t seem autofocus on the cactus. What you would do in this situation is to point the center of the viewfinder at the edge of the cactus where it overlaps the moon. The center of the camera is usually where the focus system works better than any other section of the camera. If autofocus still fails then turn on live view and to magnify the area where the moon and the cactus overlap and then manual focus there. Ok, that was pretty easy but let’s say the moon is not behind your main subject, then what? The best thing to do is to find any area on the outline of your main subject that has any kind of contrast that you can focus on. Like the rock formations in the distance that is reflecting the moonlight. You could try opening your aperture all the way and increasing your ISO, while you are trying to focus using your eyeballs. Note that increasing your ISO should not help your autofocus because it actually does not help the camera see better. This is why adding more light to the subject is much more helpful.
For those of you shooting mirrorless and think that all you have to do is turn on focus peaking or Zebra stripes available to help you with manual focus. It's a nice thought, but remember this is the same system being used in autofocus. If your autofocus failed, then the focus peaking will fail you too. At this point if you still cannot find focus it’s time to throw hail Mary’s. While you are in manual focus look at your distance scales window and to guess the distance between the camera and main subject and manually put it there. Take a photo and then check the focus on the photo. If your main subject is not in focus look for areas further away and closer to determine where you actually landed the focus and then adjust against that. Keep doing this until you get the focus you want. If you are lucky you will nail this by the second try. If you're really lucky you'll nail it on the first try, but realisitically it will probably take three to four shots.
By the way, stopping down and trying to use increased depth of field is not really a great solution as your exposure may already be pretty long as it is. Remember it was so dark that your camera had a tough time focusing to begin with, and so reducing the light further will be create more challenges on the time side of the exposure. However, you could increase your ISO by 5-8 stops and open your lens all the way just for your test shots while you check your focus. And then return to your desired settings for your final shot after you've nail your focus.
Lastly, what about just putting your lens on infinity focus? This is a good option if you are shooting something that is at infinity focus. But you should know that putting your focus ring on the infinity sign or rolling until your ring stops, without having tested this first may fail you dramatically. Because that may not be where infinity is. I’ll get into infinity focus in the next podcast but for now just know that this is not an option unless you have tested for infinity.