Low-Light Photography

(I was going to call this article “Prints of Darkness”, but good sense prevailed…)

The subject is low-light photography. This doesn’t mean that it’s time to pop up the flash and fire away, but that it’s time to get out the tripod or brace against a wall and fiddle with all those settings that you were wondering about! Low-light photography can be fun and allow for some real creativity. It can be as easy as setting your Point & Shoot on the edge of a table with the self-timer on or require hundreds of shots while you practice panning.

Light as your camera knows it

 Available light is measured in a unit called an Exposure Value or EV. The EV scale runs both ways from zero and the meaningful range is from about EV-6 to EV20 with every whole number increase or decrease representing twice or half the amount of available light (a room that measures EV6 is twice as bright as one that measures EV5). The metering range that most cameras will meter accurately runs from about EV2 to EV16 with some DSLRs covering EV-2 to EV20. For reference, here are some real-world examples:

EV-6 Scenery away from city lights full starlight
EV-2 Light colored scenery under full moonlight
EV1 Distant buildings/skyline
EV4 Streets with street lamps – people near a bright birthday cake
EV5-EV6 Home interiors with normal lighting – bright campfire
EV8 Well-lit football or baseball stadium
EV11 People or objects in open shade on a bright day
EV14 Full moon at night with a telephoto (huh?!?...will explain later)
EV15 Subjects in high, direct or hazy sun.
EV16 Sunlit snow or bright sand


Keep in mind that while a camera may only be able to meter down to EV2, there’s nothing stopping you from taking pictures in much lower light if you understand exposure. Since EV numbers only represent the amount of light available, we need to understand how the various settings on your camera translate that available light into a properly exposed image.

Exposure

 The two factors that determine how much light reaches your sensor (or film) are aperture and shutter speed. The factor that determines how quickly your camera absorbs that light is the ISO rating of your sensor (or film). These three factors are used to adjust your camera to the level of light illuminating your subject (EV). Let’s look at each of these factors individually before we start mixing them.

Aperture

 An aperture is a hole. It doesn’t get any simpler than that. It can, however, get a bit more complicated. On a lens designation, the aperture range is indicated by the letter "f" (Times New Roman, italic). A 50mm f/1.4 - 22 lens has a focal length  of 50mm (see the section on focal length in my article on Adding Lenses), a maximum aperture of f/1.4 and a minimum aperture of f/22. Uh oh…here’s the first terminology hurdle. The maximum number is smaller than the minimum number. Why?

The lens f-number (usually called an  f-stop) is a ratio determined by dividing the diameter of the hole (aperture) in the lens body that lets light in by the focal length of the lens. A 50mm lens with a 25mm aperture would have an f-number of 2.0. The larger the aperture in relation to the focal length, the more light can pass through the lens and strike the sensor or film. Lenses have variable apertures that are adjusted by a diaphragm mechanism (see picture). Standard f-stops are 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11, 16, 22 and 32. Because each stop number represents a ratio that includes a diameter, each f-stop numerical increase (2.8 to 4.0 for instance) represents a reduction in the size of the aperture and cuts the amount of light reaching the sensor in half. Each f-stop numerical decrease doubles the amount of light reaching the sensor. A step up or down that halves or doubles the exposure is called a "full" stop. Many cameras allow aperture to be adjusted in increments less than a full stop (i.e. f/6.3 is a half stop between f/5.6 and f/8). In case you were wondering, it's called a "stop" because the manual aperture rings on lenses have detents, or a "stop" that hold the ring at the chosen value.

Note: Zoom lenses will often have the f-range indicated by f/4.5-f/6.3 to f/16-f/22. This means that the maximum aperture changes as you zoom. At 70mm it will be f/4.5, but because of the change in the aperture/focal-length ratio, it's only f/6.3 at 300mm. Same with the minimum aperture on some models.

Now that we know what determines how much light reaches the sensor, let’s see what determines how long the sensor is exposed to the light.

Shutter Speed

 The shutter on a camera is usually a light series of blades that move very quickly to open, which exposes the sensor or film to light, then closing to stop the exposure. When I say quick, I mean quick. Even Point & Shoot (P&S from now on) cameras usually have a top shutter speed of 1/1000s ("s" = second) and the higher-end DSLRs can expose for as little as 1/8000s (the film-based Minolta Maxxum 9 could do 1/12000s!) On the other end, P&S camera are often limited to a maximum exposure of 4 to 15 seconds with DSLRs mostly able to do 30 seconds. Some P&S and most DSLR cameras have a “B” or “Bulb” mode that locks the shutter open for as long as you hold the shutter button down for very long exposures. Note: It’s called bulb mode because in the days of real flash bulbs, you would lock the shutter open in a dim environment, fire off several flashbulbs to light the scene and then close the shutter. Standard shutter speeds in the days of mechanical shutters were typically 1s, ½s, ¼s, 1/8s, 1/15s, 1/30s, 1/60s, 1/125s, 1/250s, 1/500s and 1/1000s. Since each step on the scale allowed the film to be exposed for half or twice as long (this is also considered a full stop, just like the f-number), the values have carried over to remain as standard settings in the current era of digital sensors and incredibly accurate electronic shutters. (You may set your dials or menu to f/8 at 1/500s, but the actual shutter speed could be 1/462s). Now, we look at the final factor in exposure.

ISO Sensitivity

 Back when photography was a new toy, photographers would prepare a light-sensitive gel and spread it on a flat glass plate (appropriately called a "wet-plate"). They would then test it to see how long it took to properly expose it. This often had to be done with each batch and was a bit of a pain. With the advent celluloid roll film and mass-produced cameras making photography available to most people, the need arose for some way to know how to properly expose store-bought film without a lot of testing. Eventually the American Standards Association (ASA) developed a sensitivity scale that all film makers could use, assuring that any film purchased with an ASA rating of 100 would perform like any other ASA100 film. In Europe, they used the German DIN standard. In the late-eighties (1987?), the ASA standard was adopted by the International Standards Organization (ISO, though the group is officially named the International Organization of Standardization) and the rating was changed to ISO for everyone. Modern digital sensors rate their sensitivity using the ISO film standard, so ISO100 on a DSLR will expose like ISO100 film. Since film had standard values like ISO25, 50, 64, 80, 100, 160, 200, 400, 800, 1000 and higher, digital cameras followed ISO's lead and set the standard sensitivity level steps at 100, 200, 400, 800, 1600, etc. with each step increase or decrease doubling or halving the sensitivity of the previous one (again, equaling a full stop). Sensors, unlike film, aren't limited to a single ISO sensitivity level. A sensor that normally has an ISO100 sensitivity can be set to ISO200 sensitivity and will capture the same amount of light in half the time. (As with the shutter, the ISO is electronically controlled and some cameras can be set at values between the standard settings.) This particular doubling comes with a price. In film, doubling the speed meant making the light-sensitive crystals larger to increase sensitivity. By the time you got to ISO800 or so, the pictures were showing noticeable graininess. At ISO3200, they looked like they were printed on 60-grit sandpaper. The same is true for digital sensors. Most have a base ISO of 100-200 and for higher sensitivity, the signal from the sensor needs to be amplified. Just like an audio signal, the more you amplify, the less true the signal becomes. The result is “digital noise”, which manifests as graininess similar to film grain. Modern DSLRs can produce excellent images at ISO speeds up to ISO3200 and above. Because of their smaller, more densely-packed sensors, P&S cameras begin to be affected by noise at lower sensitivities, much the same as film cameras. Good photos at ISO800 are rare for most of them. Not to worry! The best quality for either is at or near the base ISO, so shooting at the lowest ISO possible is always a good idea. While you can use ISO3200 for this class, you most certainly don’t need to. It’s time to assemble the pieces.

The Trinity of Exposure

 Back before we had evaluative, multi-segment metering (or whatever buzz-words your camera maker uses to tell you how smart your camera is) and tiny supercomputers in our cameras, people who couldn't afford a light meter often had to use rule-of-thumb to get the correct exposure. One such rule was the “Sunny 16” rule. It went like this; if your subject was in the open on a sunny day (EV15) you shoot at f/16 with the shutter speed set to the reciprocal of the speed of your film. If you were using ISO100 slide film, your setting would be f/16 at 1/125s (the closest standard setting to 100) and you could expect a reasonably good exposure.

If you change any of the three values, you must change at least one of the others to get the same exposure. The chart illustrates this by shifting the exposure components up and down. Keep in mind that all of the settings listed in the chart will result in the same exposure. For the P&S owners reading this, don’t worry that your camera’s aperture only goes down to f/8 or so. The numbers in the chart were used for illustration (and because the math was easy.)

So, let’s start figuring out where we need to go for our low-light adventure.

Sooooo…Slooooow!

Note: the following math is for illustrative purposes to highlight the concept of exposure and how each of the three components relate to each other. Thanks to the miracle of modern cameras, you will never have to do any of this in the field, just read the settings!

On a sunny day, f/16 at 1/125s using ISO100 works fine. Let’s drop to EV6 for the interior of a cruise ship promenade. We’ll assume f/4 for a maximum aperture since almost all cameras, whether DSLR or P&S, have lenses that will go there (many go another stop to f/2.8). Since we are still shooting at ISO100 and dropping to EV6, we need to open up that aperture and slow down the shutter. Since EV6 is 9 stops or 512 times dimmer than EV15 (15 – 6 = 9, 29 = 512), we need to make a significant change. Opening up from f/16 to f/4 only lets 16 times the light in (4 stops, 24 = 16), so we need to slow the shutter down by 5 stops to reach the proper exposure (5 stops 25 = 32, 32 x 16 = 512!). Here's a little illustration without the exponents:

What we ended up with is 1/4s at f/4. With a shutter speed that slow, is it any wonder low-light photos often come out blurry?

So, what do we do?

If you shift the ISO up to ISO400 (4 x 100), you need to divide the shutter speed by 4 (1/4 / 4 = 1/16) and set it at 1/15s (closest standard, remember?) 1/15s with a modern image-stabilized DSLR or P&S can do 1/15s with a little practice and a steady hand. There are many proven methods for improving low-light success. Here are some methods that have worked for me:

Basics: If you are hand-holding, turn on the camera or lens stabilization if it's available. Regardless of stabilization, hold your arms in against you body, but not so tightly that it makes you tremble. If you are using a camera with an optical viewfinder, press it against your face to steady it, but again, not too tightly. (Don't worry if all you have is an LCD. I never used the tiny peep-hole viewfinder on my SD800 and had no problem holding it still.)

Sniper-style: Lean against a wall or doorway if one is available. Press the shutter half-way down to pre-focus. Breathe slowly and stop breathing just before pressing it the rest of the way. When you press it, squeeze the button slowly until it trips and don't let up until the shot is over. Pressing the shutter down too hard will move the camera downward and letting go while the shutter is open will cause the lens to move upwards. You need to be aware of and eliminate all sources of motion.

Continuous or "burst" mode: Not just for sports and action! Set the camera on “Continuous” shooting mode, keep as still as you can, and then hold the shutter down for 4 or 5 shots. Your chances of getting a sharp one out of five is pretty good. Just delete the ones that didn’t come out.

All these methods pale in comparison to the effectiveness of removing the human element from the motion equation. For that you need support other than yourself.

Tripod or monopod: These are the most obvious. A good travel tripod or monopod is invaluable for low-light work. If you use a compact, a Joby Gorilla-pod is a small but effective option. There are even little devices that screw into the tripod socket and clamp on the edge of a table or fit on a beer or soda bottle, turning it into a camera support.

Note: If your camera has stabilization, most manuals will tell you to turn it off when the camera is on a tripod. Stabilizing systems can cause motion-blurring by trying to correct for motion that isn't really there.

Table-Pod: Set the camera on the edge of a table, bench or planter and set the self timer. Compose the shot (I've used lens caps, coins, napkins and other bits to prop and tilt the camera for composition) and start the timer. When it goes off, you won’t be touching the camera, so it won’t be affected by any vibration from your hands and you will get a sharp image.

Drink-pod: Set the camera across the top of a drinking glass setting on a table. It raises the point of view above the table, Use the self-timer as above. I hope I don't have to mention that you should not try this if the glass is full and nearly as wide as your camera!

Rail-Pod: If a safe stable spot for your camera isn’t available, you can hold it tight against a railing and trigger the shutter directly or with the timer. Trash cans, barrels, and cars offer impromptu support as well.

Gaffer's-Pod: Gaffer's tape is like high quality duct tape, but can be applied, peeled and re-applied without leaving a residue. It's main use it to control wiring and to rig lights and reflectors on movie sets, but I always carry a small roll in my camera bag. You can use it to tape your camera to a doorway, chair-back, tree-limb or just about anything. A roll of Gaffer's tape and the self-timer turns anything into a (fill-in-the-blank)-pod!

Conditions to watch for:

 Light color: Fluorescent and incandescent interior lighting can vary greatly and Auto white-balance struggles with making them work. Most cameras let you take the white-balance off of auto and use tungsten (incandescent) or fluorescent presets. If you have a lot of mixed light and just can't correct for it, black & white is always an option.

The moon: Dark sky, middle of the night, and you shoot the moon using the "sunny 16" rule!?! The moon is not sharing the night with you. You are seeing it's day side and it's reflecting sunlight like a volleyball on the beach at noon!

When in doubt, bracket: Bracketing means that you take a series of pictures of the same subject with exposures adjusted higher and lower (using the little +/- button that you were wondering about) than what your metering suggests. This is handy in tricky lighting, greatly increasing your chances of a good exposure. BTW, some cameras let you bracket white-balance as well.

Night-shot mode: Most cameras have a night-shot mode that exposes for the dark scene and then pops the flash to illuminate people or objects in the foreground. Remind the people not to move until you tell them to since the camera may be taking a full second exposure before or after the flash.

Some Examples:


Hand-held Stabilized Minolta DSLR
1/2s – f/3.5 – ISO400

Compact on continuous, braced on window frame. No flash...the engine was illuminated by the landing lights.
1s – f/2.8 – ISO100

8:30 PM in December – full dark, slight moon. Trees were barely visible with naked eye!
DSLR on tripod
30s – f/4 – ISO200

Fireworks after dark
DSLR on tripod
10s – f/8 – ISO100

Night-shot mode.
Sony DSLR hand-held with pop-up flash
1/6s – f/4 – ISO800

The moon needs to be exposed as if it were in daylight. Moon before sunrise.
Sony DSLR - tripod & telephoto
1/100s – f/8 – ISO100

Dim restaurant interior.
Compact on table edge with self-timer
1/2s – f/2.8 – ISO100



As you can see, whether you use high-end equipment or a pocket camera, you can get interesting images with a little practice and ingenuity. Let’s look at some other uses for low-light photography. Here are some more examples with exposure information:



Add surrealism to ordinary scenes. Like this thermonuclear Christmas tree.
Minolta digicam on a tripod.
10s – f/4.5 – ISO100

Turn flowing water into a veil. This is very good with fountains too.
Compact camera braced on railing.
1.6s – f/16 – ISO200

Follow a moving object (panning) to impart a sense of motion. This was shot well after sunset.
Sony DSLR. Stabilization turned off.
1/8s – f/5 – ISO400

Didn't really need another panning shot, but I really like this one!
Under streetlights, Minolta DSLR.
1/2s – f/2.8 – ISO200

Emergency fireworks shot at Disneyland.
Hand-held compact using continuous shooting mode.
1s – f/5.6 – ISO100

Show motion by making your own low light with a small aperture, low ISO and a polarizer.
Minolta digicam, hand-held.
1/15s – f/11 – ISO64

Make people disappear from public areas. Ten seconds will remove all but the laziest people from a mall or promenade.
Minolta DSLR, braced on a barrel.
2.5s – f/16 – ISO400

Un-corrected natural light can add warmth.
Low room light. Compact braced on chair-back.
1/20s – f/4 – ISO100

Play with your food!
Compact propped on the table.
1/5s – f/2.8 – ISO100

Shots from a moving vehicle in low light can produce interesting effects.
Late twilight. Sony DSLR, braced on railing.
4s – f/16 – ISO100


Conclusion

 Now that you have some ideas brewing in your head, go out and try them out.

Happy shooting!

 Dave