Focusing in the Dark

Among the first hurdles for night photographers is how to focus the camera in the dark. Unfortunately, you never really get over this hurdle. There are only varying degrees of frustration!

If you’re young and have excellent vision, you can probably focus visually at night on subjects that are fairly well lit, such as street scenes, or night sky scenes that include bright stars or planets. But if you have eyes like mine, or if you are shooting a subject that is very dimly lit, looking through the viewfinder and manually turning the focus ring is not a good option. I can’t even use my eyes to focus during the day, so focusing is a major issue for me at night.

I’ve listed the following focusing methods in rough order. The first one is the ideal method of achieving sharp focus. If that doesn’t work, try the next one, and so on. This is MY order of preference. Yours will be different, based on your eyesight and your style of shooting. Also, the method you use will hinge on how far away the subject is.

All of these methods are for focusing standard camera lenses and shooting wide-angle to moderate telephoto scenes without the aid of a computer. Astrophotographers use advanced methods for focusing using laptops or special focusing aids attached to their telescopes or camera lenses. That’s the subject for another article.

Remember that in some situations it is perfectly acceptable to focus on an object that is outside your composition. For instance, you may be shooting a star scene where there are no bright stars within your frame of view. Simply point your camera outside the view to a bright star or planet and autofocus on it, then recompose, making sure you don’t change the focal length after you get the focus set (see #8). As long the object you focus on is the same distance away as the subject, you’ll be fine. And if your subject is a few hundred feet away or more, you have a lot of leeway. 

1. Focus during the day.

In a perfect world, we’d be able to set up our night compositions before it gets dark. That way, you can get the focus set and fine-tune the composition without any trouble. Of course, this is rarely an option, and even when it is, it only works for the first composition of the night.

2. Autofocus on an existing light in the scene.

Autofocus works on many objects at night, such as streetlights, the moon, and Venus and Jupiter. Some cameras will even autofocus on bright stars as long as you are not using an extremely wide focal length.

3. Illuminate the subject so you can autofocus on it.

If the subject is close enough, you may be able to shine a bright flashlight on it and use autofocus. If you have snoot for your flashlight (a cardboard tube to channel the light, like a gun barrel) it will help project the light in a bright tight spot for the focus to lock on to.

4. Autofocus on a laser pointer.

If the subject is too far away to illuminate with a flashlight, or if it is a dark subject that absorbs light, you can create a focus point by shining a powerful laser pointer on the subject. I use this method often. The only catch is you have to have a good laser pointer and you have to keep fresh batteries in it. Green lasers work better than red ones because they are much brighter. Mine is so powerful that it produces a visible beam of light projected into the night sky as long as the air isn’t too clear. Makes me kind of feel like Luke Skywalker wielding a light saber!

User a laser pointer is serious business and if you aren’t careful it can have dire consequences. NEVER shine a laser into the sky if there is any possibility of airplanes being near. This is a felony offense, and if you don’t think they’ll find you, think again. Also, it should go without saying that you should never shine a laser at a person or animal.

The widely available laser pointers used for slide shows and general amusement are labeled Class IIIa and cannot be more than 5 milliwatts in strength. This is not powerful enough for most focusing situations. You’ll need a Class IIIb laser, which can be from 5mw to 500mw. Mine is 200mw. To be legal in the U.S., a Class IIIb laser cannot be promoted as a “laser pointer” and must have appropriate warning labels and safety devices. A quick Google search shows that this regulation is widely ignored, even from companies operating in the U.S. Again, this is serious business and the best advice I can give is to do some research before you buy and make sure you understand what you’re getting and the safety issues applicable to it.

5. Add a light in the scene and autofocus on it.

If the subject is only a few hundred feet or closer, you can add a bright light to the scene and autofocus on it. Simply set your flashlight on the ground along the same plane as the subject and point it at the camera.

6. Live View.

The Live View feature of some cameras is extremely useful for focusing in situations where you have a distant light that is not bright enough on which to autofocus. Magnify the light to its maximum magnification on the screen, and then manually turn the focusing ring until the light is at its smallest point size, which indicates sharp focus. It can be very difficult to locate faint stars in the Live View screen. Before looking at the screen, set the focus ring initially to the infinity mark. Then gradually increase the magnification on the Live View screen as you scroll around searching for stars. If the focus is not set close initially, the stars will be invisible on the screen at even moderate magnifications.

You can also use Live View in conjunction with a laser pointer. A pointer that is too weak for autofocus to grab on to might show up on the Live View screen. Also, remember that Live View will work with ANY light in the scene, not just distant ones. I only use it for the distant lights because autofocus usually works for the closer lights and is much quicker.

7. Trial and error.

If all else fails, you can always make a wild guess, shoot a test shot, review the result on the LCD, and keep changing focus until you get it right. The problem with this method is that it is very time consuming and difficult to get it just right. It’s very hard to judge precise focus on the LCD; you just have to set it at what looks like sharp focus. You can make this process go quicker by boosting the ISO way up so your shutter speeds are shorter.

You could always download the shots on your computer or a larger viewing device to make it easier to determine whether they are in focus, but boy, talk about a tedious and time-consuming process. I’d do everything I could to make #1 through #6 work before resorting to this method.

8. Manually set the focus ring.

In many texts, this is the first method the author recommends for focusing at night when the subject is at infinity. Simply rotate the focus ring until the infinity mark lines up with the focus mark and you’re all set. What could simpler? Well, nothing could be simpler, but it sure could be a lot more accurate! In fact, using this method is so hit and miss that I use it only as a last resort, and then only in combination with the trial and error method.

There are four problems with this method. First, simply lining up the infinity mark doesn’t necessarily mean you are setting the focus precisely at infinity. Lenses aren’t manufactured to tolerances so tight that every one of those marks is precise on every lens. It could be just a smidge (or more) off the mark. The second reason is that the focus point can actually change slightly based on temperature, so even if it is precise at a certain time, it might not be at another. The third reason is that since you are manually setting the focus ring and there is no click stop, there is the possibility of setting it a smidge off.

The fourth reason is the big one. Most zoom lenses produced today are varifocal, which means the focus point, including infinity focus, changes with focal length, as opposed to parfocal, which means the focus point remains fixed. So while you could go out during the day and focus on a distant object to see where the infinity mark lines up on the lens, it would be accurate only at that particular focal length. Yes, with a fixed-focal-length lens, a test like this would work, but you’d still have the second and third issues confronting you. Nearly every lens I own is a zoom and only one of them is parfocal, an old Nikon 70-180 Micro lens. Even with it, the focus changes slightly due to small inaccuracies with the internal mechanics. It is simply not practical for me to perform an infinity mark test for every lens at every focal length, especially since those marks could change from winter to summer. 

By the way, if you’re thinking that being just a smidge off on your focus at infinity isn’t such a big deal, go out and make a test shot of the stars with a moderate to long telephoto lens. Shoot one exposure where you know the focus is dead-on, then shoot another where you shift the focus ring just a smidge. View them on your computer at 100 percent or higher magnification and see what you think. Granted, with a wide-angle lens the difference might not be extreme, but it still could cause problems if you wanted to make large prints. Besides, wouldn’t you want the focus to be as sharp as possible with every shot?

Final considerations.

Okay, so you got the focus set and now you can start shooting. Not so fast, we’re not done yet. If you’re shooting a scene that requires very long exposures or multiple exposures, such as star trails, it’s a good idea to TAPE THE FOCUS RING IN PLACE once proper focus is attained. You will be surprised at just how many ways the focus ring can change during the night, either from an inadvertent grab of the hand or the ever-present gremlins that hang out with you while you shoot. Gaffers tape or painters tape works best because it does not leave a residue.

Regardless of your focusing method, it is critically important to TURN AUTOFOCUS OFF once proper focus is obtained, even when the focus ring is taped in place. Otherwise, depending on how you have your camera set up, when you press the shutter release the camera will try to autofocus and you’ll lose your setting. Note that with some lenses it is still possible to autofocus while the focus ring is taped in place. In fact, since I use autofocus for all daytime shooting, I have often shot all day using some of my lenses with the focus ring securely taped. Again, make sure that autofocus is turned off before you make your night exposures.

Okay, get out there and focus on what you’re doing!

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