Modern digital cameras with their lightning quick phase detection and contrast detection auto-focusing mechanisms are really good when it comes to locking focus during the day time. At night time though it is a completely different story. More often than not your camera will hunt for focus, struggling to find something with contrast to lock on to. This is the time when you need to use a bit of innovativeness to figure out how to nail focus. Here are some tips that should help.
A Word on Camera AF points
Normal AF sensors look for contrasts in one axis only. You may have heard about the term vertical line sensor. These sensors can look for contrasts horizontally only. It means if the horizon is a bit darker than the sky it is likely going to lock focus easily. However, if you are aiming towards a dark sky with no discernible contrast it would continue to hunt for focus.
Dual axis sensors can look for contrasts not one but two directions. These sensors are also known as cross-type and are more sensitive than the line sensors. Usually the professional models of cameras have these with some cameras having all cross-type AF points. Some enthusiastic model have the center AF point as cross-type.
Tips and techniques to lock focus at nighttime / low light – Find something to lock focus on
A bright spot, something in the middle of darkness to form a contrasty edge, anything really that brings into play the focusing mechanism of the camera. If you are shooting in live-view the system would be using contrast detection auto-focusing, which is slower. Otherwise, it would be using the phase detection auto-focusing system which is faster but less accurate in low light conditions.
Trust your Eyes and use Manual Focusing
Either you use auto-focusing wherein there is a chance of focus hunting or you trust your eyes and back yourself by opting for manual focusing. With manual focusing at least you don’t have to worry about your camera going into the dreaded focus hunting scenario. Even if something goes wrong you have the benefit of reviewing an image and taking another shot if necessary.
Manual focusing helps you in yet another way and that is, you don’t have to rely on the focus and recompose technique. You can simply compose your scene and then use manual focusing.
Use a Small Aperture / big f-number
One of the things that you should do when trying to lock focus manually is use a big f-number. Bigger f-numbers brings more of the scene into focus by accentuating the circle of confusion and eliminating the chance that your subjects could be out of focus. Even if they are, by a margin, it wouldn’t matter at the end because the human eye has a bit of tolerance.
Shoot with a Wide Angle Lens
Wide angle lenses not only have a big angle of view but they also tend to offer a big depth of field. All the more reason why they are preferred for night time shooting. Be it fireworks, star trails, Milky Way, light trails, cityscapes or even shooting the northern lights, wide angle lenses are better suited that their tele-lens brethren.
Using the Focusing Distance Scale
The focusing distance scale on some lenses is a neat feature to have. It allows you to set your focusing distance with a tweak of your fingers. Sometimes, pre-focusing becomes essential because the subject you are about to focus for isn’t there at all! Let’s say you are trying to shoot the Fourth of July fireworks. Before the fore-works begin there is nothing to lock focus on. You can make some wild guesses but they are as good as any. The only way you can logically make a sensible focusing estimate is by using the focusing distance scale.
Live view gives you a bigger view to play with. If you are using manual focusing you can trust live-view more than the small viewfinder and accurately lock focus. It is a whole lot easier too, especially when you are using a tripod.