Night / Bulb —
Long Exposure Practice

The bank used for night photography is the subject-driven choice, not the technique-driven choice. The technique addendum below applies regardless of bank. Choose the bank whose base configuration matches the subject most closely and adjust the specific long-exposure settings within that bank's framework.

GF 100-200mm F5.6 note: the lens is valid for night work when the subject is distant and compression is the point — illuminated rooflines, compressed city lights, moon-adjacent landscape details, or distant architectural fragments. Treat it like the other OIS zooms: on a tripod, barrel OIS OFF and camera IS MODE OFF; handheld or monopod documentary use belongs back under the C3/C4 stabilisation logic.

The GFX 100S II at 102 MP is a demanding long-exposure camera in one specific sense: its large pixel count at the GFX pixel pitch (3.76μm) accretes dark-current noise over long exposures at a different rate to smaller-sensor systems. The noise character is well-behaved and easily managed in Lightroom, but the discipline of exposure management matters more than it does on cameras with smaller pixel counts and more aggressive in-camera NR defaults.

ISO discipline for long exposures

Use ISO 80 or ISO 100 for all long exposures where the exposure time achieves correct brightness. The GFX 100S II's extended base ISO (ISO 80, accessible in M mode) offers the maximum dynamic range and the lowest base noise floor. There is no benefit to using ISO 200 with a shorter shutter time if ISO 80 with a longer time achieves the same brightness — the longer exposure at lower ISO produces a cleaner file.

For star trails and Milky Way exposures, ISO 800–3200 is sometimes necessary to capture the sky within a practical single-frame duration. At these sensitivities the GFX 100S II performs well for a large-sensor system. ISO 3200 on the GFX 100S II produces files that remain printable at large formats where smaller sensors would require aggressive NR that softens stars and texture.

Long Exposure NR: the practical rule

Long Exposure NR applies a dark-frame subtraction to the exposure — it takes a second exposure of equal duration immediately after the main exposure, with the shutter closed, to map the sensor's dark-current noise pattern and subtract it from the main frame. The effect is a measurable improvement in dark-current noise, particularly in shadow regions and very long exposures.

The cost is session time: it doubles the exposure duration. A 4-minute star-trail exposure requires an additional 4-minute dark frame. During golden hour, this is unacceptable — two exposures consume the peak light window. At night, with no time-critical light, it is often acceptable and recommended for single-frame exposures beyond 2 minutes.

Sensor temperature and thermal noise

At exposure durations beyond 5 minutes, sensor temperature rises and hot pixels begin to appear — fixed-pattern bright pixels that dark-frame subtraction typically removes, but which become more numerous as temperature increases. Allow brief pauses between consecutive long exposures during interval sequences to prevent thermal accumulation. 10–15 seconds between interval frames is typically sufficient. Do not seal the camera body in an insulating bag or backpack between exposures — ambient air cooling is the thermal management strategy.

Star trails record the apparent motion of stars across the frame due to Earth's rotation. The GFX 100S II at 102 MP resolves individual stars to approximately 2–3 pixels at a good seeing site — a trail length of 20 pixels or more is clearly visible as motion. The geometry of this motion determines exposure duration and framing strategy.

Earth rotation and trail geometry

The Earth rotates at 0.25° per minute (15° per hour, 360° per 24 hours). At the celestial equator, stars appear to move at this full rate. At higher declinations (toward the poles), the apparent motion rate decreases. Near the celestial poles, stars trace tight circles visible in short exposures; at the celestial equator, stars trace nearly straight parallel lines.

At the GFX 100S II pixel pitch of 3.76μm with the GF 20–35mm lens at 20mm (32mm equivalent), one pixel subtends approximately 0.016°. A 1-minute exposure at the celestial equator produces a trail of approximately 15 pixels — clearly visible as motion at any print scale. A 10-minute exposure produces a 150-pixel trail — approximately 0.5mm at screen viewing, visually significant even in proof images.

Interval Timer for stacked trails

The Interval Timer is in SHOOTING MENU. For star trail stacking, the configuration is: interval = exposure time + 2 seconds (to allow the camera to write the file before the next frame fires), starting frames = 0 (unlimited until stopped), start time = now. Set the shutter speed in M mode first, then engage the Interval Timer. The first frame fires immediately; subsequent frames continue at the programmed interval until the shutter button is pressed to stop the sequence.

Combine the frames in Sequator (Windows, free, designed for star stacking) or Photoshop's Layer Stack → Lighten blending mode. Lighten mode selects the brightest pixel from all frames at each pixel position — which selects the star positions from all frames while preserving the dark sky of any single frame. The result captures trail coverage equivalent to the total sequence duration.

Light painting is the practice of adding supplementary illumination to a long-exposure frame using a handheld light source moved through the scene during the exposure. The result is light applied selectively to chosen surfaces without casting shadows on adjacent surfaces — a capability unavailable with fixed supplementary lighting.

The ambient-first rule

Before painting, take a test frame at the intended shutter speed with no light painting. This is the ambient exposure. The ambient exposure determines how much of the background, sky, or environmental context is captured before the painting layer is added. The painting adds to the ambient; it does not replace it. If the ambient exposure produces a result that is already bright enough in the background, the painting must be calibrated to match that brightness — not to compete with it or overwhelm it.

Light source selection and beam character

The beam character of the light source determines the hardness of the painted edge. A flashlight with a focused beam produces a hard-edged circle of light — appropriate for dramatic accent painting, inappropriate for documentary-style environmental illumination. A diffused LED panel or a flashlight bounced through white paper produces soft, spread illumination appropriate for environmental fill. Choose the light source for the edge character required, not for its brightness alone.

GFX 100S II White Balance for light painting

Fix the White Balance before painting. Auto WB attempts to neutralise the dominant light colour in each frame — when comparing a no-paint test frame to a painted frame, WB drift will produce colour inconsistency that is difficult to reconcile in post. Set a fixed Kelvin value (typically 3200–5500K depending on ambient light character) and lock it for the session.

On the GFX 100S II, the Electronic Shutter reaches 30 seconds in P and A modes, while Fujifilm's spec sheet publishes timed exposures up to 60 minutes in S and M. In practice, the 30-second mark is where many users leave the simple dial-driven workflow and start making an explicit shutter-choice decision. Beyond that point, choose between Electronic and Mechanical based on rolling-shutter risk, flickering light, and operational certainty — not on the assumption that Electronic is no longer available.

Bulb mode on the GFX 100S II is accessed through the shutter speed controls when a shutter type that supports it is active. T (Time) and B (Bulb) remain the key long-exposure control modes: T is the hands-free option for timed open/close use, while B keeps the shutter open for as long as the release is held and is best paired with a locking cable release for repeatable field work.

T mode vs B mode: when to use each

T mode (Time): Best for light painting. Press once to open the shutter; both hands are then free to paint through the scene. Press again when the painting is complete. No need to hold the cable release — the shutter stays open until the second press regardless. The limitation is that in pure T mode you cannot see the elapsed time from the camera body; use a phone timer or external timer to track exposure duration.

B mode (Bulb): Best for star trails and very long exposures where the total duration is known in advance and the camera must not be touched after the release is engaged. Use a locking cable release — press, lock the cable grip, and step away. The shutter remains open until the cable lock is released. The camera's live histogram continues updating during the exposure — you can check exposure progress by examining the live view on the rear LCD (though touching the LCD during the exposure can transmit vibration).