How to expose a film scan, from RAW to white balance

To expose a film scan, shoot RAW in manual mode at your camera’s base ISO, with a fixed white balance. On a negative, set the shutter speed so the clear film base, the brightest part of the capture, sits just below clipping in the brightest colour channel. Then keep exactly the same settings for the whole roll.

The settings at a glance

Setting	Use	Why
File format	RAW	It keeps all the data, with no tone curve or colour baked in
Mode	Manual	Auto exposure changes from frame to frame
ISO	Base ISO	The least noise and the widest range
Aperture	f/8	Sharp, with less vignetting and some depth of field
Shutter speed	Set from the film	The light is constant, so this is your only exposure control
White balance	Daylight, or custom from the bare light	One fixed value for every frame
Picture style	Neutral or flat, low contrast	Brings the camera’s histogram closer to the RAW data
Highlight warning	On	Shows you what clips

The base ISO is the lowest native ISO of your camera, usually 100 or 200. Settings below it, often marked L or “extended”, are not native. Check your camera’s manual.

Why RAW

A JPEG or a TIFF from the camera has a white balance, a tone curve and sharpening already applied, all made for a positive picture. When you invert a negative, those choices turn against you and distort colours and tones after inversion. A RAW file keeps the sensor data as it is, so the conversion starts from the real densities of the film.

Use a fixed white balance

In a RAW file, white balance is only a label. It does not change the sensor data, and you can change it later. A fixed setting still matters:

• Auto white balance changes with each frame. The previews and histograms jump around, and you cannot compare frames.
• Many apps start from the white balance in the file. With auto, every frame of the roll starts from a different place.
• Phone captures and camera JPEGs keep it for good. There, a wrong white balance is baked in.

Choose one of two options and keep it:

• Daylight. Simple, and the same on every camera.
• A custom white balance measured off the bare light, with no film in the holder. Nikon suggests this for slides with one strong colour, and it works for any film. It makes your light neutral, so what you see is the colour of the film.

Expose to the film base

A negative is dense where the scene was bright and thin where it was dark. The thinnest part of all is the film base: the clear film between the frames and along the edges. Nothing in the picture can let more light through than that.

So the film base is your reference. If it sits just below clipping, nothing inside the picture clips, and every other part of the negative gets as much light as it can.

1. Put a frame in the holder with some clear film base in view: the gap between two frames, or the edge of the film.
2. Mask the bare light around the film. Light through sprocket holes and gaps is brighter than the film base. It clips and can flare into the picture.
3. Turn on the RGB histogram and the highlight warning.
4. Make the shutter speed longer until the peak of the film base is close to the right edge, in the brightest channel. If the film base blinks, go back one step.
5. Lock that exposure for the roll.

If your camera has no RGB histogram, a rough rule works: use the meter’s reading, or one stop brighter, which puts more light into the dense parts of the negative.

Read the histogram per channel

A single brightness histogram can look fine while one colour channel clips. Use the RGB view, which shows red, green and blue apart.

Keep in mind where the histogram comes from. The camera draws it from its own processed preview, after white balance and picture style, not from the RAW data. With a neutral or flat style and low contrast, the preview is closer to the RAW. It often shows clipping a little before the RAW data really clips, so a small gap on the right is a safe margin.

If you want to be sure, open a test capture on your computer in an app that shows the RAW values per channel, and check the brightest channel there.

Black and white, colour and slide

Film	Brightest part of the capture	What clips first	What to watch
Black and white negative	Film base	All channels at about the same time	The base is close to neutral. Nikon’s guide notes that for black and white, the brightness of the light is all that matters
Colour negative	Film base	Red	The orange mask holds back blue, so blue sits far left. A cool light gives blue more light
Slide	The clearest highlight in the picture	Any channel, depending on the picture	Protect the highlights. The shadows are dense and close to the noise

Colour negative. The orange mask lets a lot of red through and little blue. With a daylight-coloured light, the red channel reaches the right edge while blue is still low. Expose for red, and blue gets what is left. This is why some scanning lights have a cool mode: CineStill says the cool setting of its CS-LITE reduces the orange mask.

Slide. There is no film base to read. Find the brightest highlight on the roll and expose so it does not clip. The guide to scanning slides with a camera covers dense slides and the colour of the light.

What clipping and underexposure do

• A clipped negative loses the thinnest parts of the film. Those are the deepest shadows of the final photo. If only red clips, the shadows also turn a different colour after conversion.
• An underexposed negative capture puts the dense parts of the negative near the bottom of the sensor’s range. Those are the highlights of the final photo, and after conversion they show noise and banding.
• A clipped slide loses its highlights for good.

The same settings for the whole roll

Keep the shutter speed, aperture, ISO, white balance and focus the same from the first frame to the last. Then any difference between two captures is on the film, not in your camera. Your converter, or you, can compare the frames and make them match.

There is one exception. A very dense frame can take more light, as long as nothing inside the picture clips. Note the frame number, because it then needs its own conversion. The guide to thin and dense negatives explains when that helps.

Common problems

• The conversion looks flat and grey. Stray light around the film, or an underexposed capture. Mask the light and expose to the film base. See why film scans look flat.
• Noisy or banded highlights after conversion. The capture was underexposed. Give more light, up to the film base.
• Shadows with an odd colour. The red channel clipped. Shorten the exposure until the film base stops blinking.
• Frames of one roll look different from each other although you shot them in the same light. Auto exposure or auto white balance. Switch both to manual.
• A colour cast across the roll. The light, or a fixed white balance far from neutral. See colour casts in film scans.

For the rest of the setup, start with how to scan film with a camera.

Sources

• Nikon: digitizing film using the D850 and ES-2
• CineStill: CS-LITE camera scanning light