Toby Keller - Night Photography Blog

Tutorial: Getting Exposure Right at Night

D300, 262 seconds, f/6.7, ISO 200.

“How the hell do you figure out how long to expose if it’s dark outside?!” That’s probably the most common question I am asked by other photographers. During the day, we can safely rely on the meters in our cameras or on guidelines like the “Sunny 16” rule. Once the sun goes down, though, it’s a different story… very few light meters give accurate readings after dark. And night shooting presents its own unique set of difficulties - for example, if you shoot film you have to contend with reciprocity failure, or the film becoming less sensitive to light once it drops below a certain threshold.

For the sake of simplicity I won’t get into the specifics of reciprocity failure. Instead, I’ll give you a quick rundown of how I expose at night, and a couple pointers to get you started on the right track. If you really really want to know about reciprocity failure, I recommend you check out Night and Low-Light Photography: Professional Techniques from Experts for Artistic and Commercial Success, written by Jill Waterman. It is the definitive guide for aspiring night photographers and devotes a good large portion to the concerns of film shooters.

Now, down to brass tacks. You’re outside some abandoned warehouse at 3am with a thousand bucks worth of camera gear, trying not to look to much like a terrorist, probably freezing your ass off to boot. How do you figure out how long your exposure should be so you can get back to a warm house and a glass of scotch?

There’s a few things to remember:

1. You’ve got lots of time

During the day, an exposure might be measured in the hundredths or even thousandths of seconds. If you’re off by a couple hundredths, there goes the shot. Not so much with night photography… If the proper exposure is 5 minutes, you’d have to shoot for 10 minutes to overexpose by a single stop! This gives you some serious leeway, and it’s why I’ve never bothered timing my exposures with any sort of precision. A glance at the minute hand position usually suffices. The shot below was overexposed by 300 seconds - that’s 5 minutes that I sat there talking to someone before I remembered the exposure was done. I could have pulled it back to the “proper” exposure in Lightroom, but I actually liked the result. At any rate it illustrates my point - you’ve got a lot of padding on either side of the “right” exposure.

D300, 708 seconds, f/5.6, ISO 200.

2. Set it and forget it

Especially when you’re first starting, it pays to simplify the number of decisions you have to make for each shot. Find an ISO and aperture that work for you and stick with them, at least til you’ve got the exposure thing down pat. Your ISO should generally be at your camera’s “native” ISO - for example, my D300 goes down to 100, but the “native” ISO is 200, so that’s what I shoot at night. Any higher and you’ll see a noticeable increase in noise levels, beyond what you’d see during the day. Long exposures are taxing on digital sensors, so make it easy for your camera. You’ve got more freedom when it comes to aperture - I try to use the widest (smallest number) aperture that I can while maintaining enough depth-of-field to get everything in focus. This varies with focal length - but for my 12mm lens, f/6.7 is the sweet spot. Smaller apertures (higher numbers) will give me even more depth of field, but at the cost of longer exposure times.

Once you’ve got a good working ISO and aperture, leave them there! Don’t fiddle. It’s way easier to remember what a 5 minute exposure looks like if you don’t have to juggle those other parameters too. Experiment until you get something that allows exposure lengths that you’re ok with.

3. Keep an eye on the moon

If you’re shooting away from the city, chances are you’re relying on the moon to provide light for your exposure. I generally shoot between the half and full moon, which I know from experience gives me exposure times in the 4-8 minute range. 4 minutes at the full moon, 8 at the half, and so on. Since I’ve got my aperture and ISO figured out already, I can just vary the exposure time to account for any variance in light levels - for example, an extra minute or two if there are clouds passing by.

If you’re shooting in an urban area with artificial lights, the exposure times will probably be much less. Other than that, it varies widely depending on how bright the light is, what type, and how far away it is - not to mention what kind of look you’re going for. What I do: start at a minute or so and go from there ;)

4. The ISO boost trick

So you’re out there in the middle of nowhere and a freaking deer pops up out of nowhere and freezes, staring right at you. You ain’t got time for experimentation, you need the right exposure ASAP! Ok, well, there’s a trick that might help you get there a little quicker. Try boosting the ISO as high as it will go (say 3200), and do a test exposure at thirty seconds. Ignore the noise and look at the histogram. It will tell you if you’re in the ballpark. If it’s off by a stop, take note of it, but don’t do another test shot - you can calculate the right exposure time now for your true ISO. Each doubling of ISO means exposure time is halved. So if the proper exposure was 30 seconds at ISO 3200, go like this: 3200, 1600, 800, 400, 200. That’s 4 stops. Now go the other way with the exposure: 30”, 1’, 2’, 4’, 8’. The correct exposure at ISO 200 is 8 minutes. Hopefully, the deer hasn’t fuzzed off yet and you can get the shot.

Now, once you’ve experimented for a while and you’re getting a feel for how different exposure times turn out in different conditions, forget the trick and just go with your gut. Trust me, it’s quicker. I get within a half stop 8 times out of 10 now that I’ve been doing this for a while.

You still here? Quit reading and go shoot!