Long exposure is where film quietly shows its character. Digital sensors accumulate noise as the seconds tick by, but film simply keeps gathering light, rewarding patience with silky water, smeared clouds, streaking headlights and empty streets scrubbed clean of people. The catch is that film does not respond to very long exposures in a straight line, so a little planning turns guesswork into repeatable results.

You need a solid tripod first

Everything about long exposure starts with a steady tripod and a way to fire the shutter without touching the camera — a cable release, a self-timer, or a locking remote. Any vibration during a multi-second exposure smears the whole frame. Weigh the tripod down in wind, hang your bag from the centre column, and if your camera has a mirror lock-up feature, use it to remove the tiny shake the mirror makes when it flips up.

ND filters: buying darkness

To keep the shutter open for seconds or minutes in daylight, you must cut the light reaching the film with a neutral density (ND) filter. NDs are rated in stops: an ND8 is 3 stops, an ND1000 (often called a 10-stop) is the classic choice for daytime long exposures, turning a 1/250 exposure into roughly 4 seconds. Strong NDs let you blur water and cloud in broad daylight. Meter the scene without the filter, then add the filter's stops to your calculated time. A phone app or a printed table makes this quick, and a variable ND is convenient though it can cause colour casts and cross-shaped darkening at extreme settings.

Reciprocity failure: film's own rule

Here is the part unique to film. The reciprocity law says a given amount of light produces a given exposure regardless of how it is delivered, but at very long exposures film loses sensitivity and this breaks down. Your meter might say 8 seconds, yet the film needs 20 or 30 to record the shadows properly. This is reciprocity failure, and every film handles it differently. As a rough guide:

  1. Meter normally and note the indicated time.
  2. If the indicated time is longer than about one second, add exposure according to the film's data sheet — often expressed as a corrected time or an extra stop or two.
  3. Favour films that hold up well in long exposures. Fuji Acros II is famous for needing almost no correction up to about two minutes. Colour films like Portra and Ektar need correction and can shift colour, while traditional emulsions like Tri-X or HP5 need generous extra exposure at long times.

Bulb mode for minutes

Cameras top out at 30 seconds or so on their timed dial. For anything longer you use Bulb (B), where the shutter stays open as long as you hold the release. With a locking cable release you can time exposures of minutes by the clock. Bulb is how you record star trails, painted light and long nocturnes; just watch battery drain on electronic shutters, since many keep the shutter open by drawing power the whole time.

Putting it together

A typical daytime long exposure runs like this: compose and focus, meter the scene, calculate the base time, fit a 10-stop ND and recalculate, then apply reciprocity correction from the film's data. Lock the shutter open on Bulb if you need more than 30 seconds. Bracket your first few frames generously, because reciprocity is the hardest variable to predict, and keep notes so your next roll is a calculation instead of a guess.

Focusing and metering in dim light

Long exposures often happen at the edges of the day or at night, where focusing and metering get harder. Focus before you fit a strong ND filter, because a 10-stop filter can make the viewfinder too dark to focus through; lock focus, then attach the filter without touching the ring. For metering in very low light your camera's meter may run out of range, so meter off a brighter part of the scene, use a handheld meter, or bracket widely and read the results. Manual focus and a small aperture like f/11 give you depth of field to cover small focusing errors, which is welcome when you cannot see clearly through the finder.

What to shoot and how it looks

Different subjects reward different exposure lengths. Moving water smooths into mist over a few seconds and becomes glassy over thirty; a waterfall needs far less time than a calm sea. Clouds streak across the frame over a minute or more, giving landscapes a sense of motion and time. At night, car headlights and tail lights draw continuous ribbons of colour through a scene, and busy streets can be scrubbed almost empty of people because anything that keeps moving never stays in one place long enough to record. Choosing your exposure length is therefore a creative decision as much as a technical one: decide how much blur tells your story, then work back to the filter and time you need.

Star trails and the very long night exposure

The ultimate long exposure is the star trail, where the Earth's rotation draws the stars into arcs across the sky. These exposures run from many minutes to hours, far beyond where reciprocity failure matters, and are best built on Bulb with a locking release, ideally away from light pollution. Many photographers now shoot a long sequence of shorter frames and stack them digitally to avoid a single hours-long exposure fogging, but a single long frame on film has a character of its own. Whatever the subject, a long exposure asks for patience and rewards it, so slow down, plan the frame and let the film do the gathering.

If you need an ND filter, a cable release or a sturdy tripod for your next long-exposure session, Boston Camera can set you up and check that it fits your camera before you head out.