Exposure is a key concept in all types of photography. Particularly film, where you can’t see your images until you develop them.
This guide explains exactly what makes for a correct exposure, what it means for the final image, and how to set yours properly.
We’ll begin by defining “thin” and “dense” film negatives and how those concepts guide a common photographer’s advice to meter for shadows. This knowledge is then expanded with a more precise selective metering method and its relationship with 18% middle grey and films’ dynamic range limitations.
Finally, I will discuss the meaning of a “correct” exposure: an exposure that retains the maximum amount of detail in the areas of your interest.
“Thin” vs “dense” film negatives.
When negative film is exposed and then developed, areas that received light appear dark and opaque — this is where the silver halide crystals form what we call film grain. Light or transparent areas on developed film negatives (often referred to as “thin” areas) would’ve had less light exposure and thus retain fewer crystals. When there isn’t enough light to activate the crystals at all, the emulsion is left completely transparent — devoid of any light information.
Areas of developed film that received a lot of light appear very dark, bustling with crystals (often referred to as “dense”). It may be difficult to discern shades in those places but they are usually more useful than areas where there are no crystals formed. You can think of dense areas as pictures painted with barely distinguishable shades of black paint on black canvas: it may be difficult to tell what’s in there but it is surely is better than a completely blank canvas with no image at all.
In short, there’s generally a better chance of restoring over-exposed images (i.e. “dense” negatives) upon scanning or printing than under-exposed ones (i.e. “thin” negatives). Note that this rule is reversed for slide/positive film.
Metering for shadows.
Some photographers advise beginners to point their light meters towards shadows. This tends to exclude some of the brightest spots from the meters’ calculations, giving readouts with longer shutter speeds and wider apertures. This technique attempts to ensure that the darker areas, which often suffer from loss of detail are given more light, assuming that the bright/dense spots retain enough information.
In my experience, however, metering for shadows does not guarantee good results. In fact, if you are to point a spot meter towards the dark spot in a brightly lit scene, your image is likely to get severely over-exposed with that reading.
As mentioned above, “dense” negatives are preferred as they may retain some information as opposed to “thin” ones. But there’s a limit to this that is easily crossed by thoughtless light measurements that ignore bright areas in hopes of avoiding under-exposures.
Best exposures are made by ensuring that your key subject has an optimum amount of light on film. After all, that’s what/whom you’re photographing, and you want the most amount of visual information on film for those parts of your scene.
Everything that surrounds your point of interest is there to support it and thus should take a back seat as you meter your scene.
The best tools to make these kinds of measurements are spot meters, incident light metres, and your own eyes.
Spot metres measure reflected light off your scene within a narrow angle — a spot. They are helpful in getting selective readings, although they do not always come built-in to your camera. In which case, I suggest you download an app for your mobile device like Lumu, which I’ve been using for many years. Light metering apps can be more accurate than built-in meters; they often have spot-metering options, and they let you preview your scene at the given exposure, which is very helpful.
You should, however, remember that spot metres expect to be pointed at an 18% middle grey area (see below). This means that if you’re pointing at something white, your readings may cause under-exposures in mid-tones and if you’re pointing at something black, your readings may cause over-exposures. There are two things that you could do in situations like this: 1) find something in your scene that looks like a middle grey and meter off it instead 2) estimate how many stops your focus point is darker/lighter than the middle grey and compensate your light meter’s reading with that.
For example, the mushroom in the photo above is a very light grey thus I pointed my spot meter at it and compensated my reading by an estimated +1 stop to make sure that it stays bright in my exposure. The initial reading at 𝒇2 gave me 1/125s shutter speed, after the compensation, it has become 1/60s. Knowing the precise amount of stops you need to compensate for takes a bit of experience. Practicing by taking casual readings with a light meter app on your phone helps — doing this will teach you to get a sense of what a stop of light means in the real world.
Incident light meters are fantastic for complex light readings because they don’t rely on what you pointing at to be an 18% grey — so you don’t have to worry about compensating. Instead, they measure the available light where you’re metering. If I were to use it on the same mushroom from above, I’d have to walk up to it and hold the incident meter right next to its hat, pointing towards the light source. This isn’t always practical, particularly when you photograph subjects that are far away or you’re trying to take a fast measurement. Incident light meters also tend to be more expensive.
Sunny 16 rule guarantees a good exposure if your subject is in the full sun, you set your aperture to 𝒇16, and your shutter speed is an approximate 1/film ISO. For example, an ISO 100 film in the full sun at 𝒇16 would expose best with 1/125 shutter speed. Of course, you can change your camera setting to 𝒇8 (add +2 stops of light) & 1/500 (-2 stops) to get the same exposure. With practice, you may learn how to eventually measure most light conditions by just looking at your scene, though it does take time.
18% middle grey.
Each scene with white and black points has a variety of scattered shades. If we are to sort them and arrange them in a line according to their brightness, where 100% is white and 0% is black, an 18% mark will be perceived by the human eye as the “middle” brightness.
A light meter will analyze your scene and use the 18% mark as a guide to set your camera’s shutter and aperture values so that the middle grey approximately matches the midpoint of your film’s dynamic range. For example, for an ISO 100 film, your light meter may read out an aperture of 𝒇8 and shutter speed of 1/500th of a second on a bright sunny day.
Your film’s dynamic range.
Film can only capture a limited range of light intensities. Knowing its exposure gamut/dynamic range will help you select the right materials for better exposures.
A wide dynamic range film will capture more details in a scene with a mix of dark shadows and highlights.
A narrow dynamic range film can help you get the details on a single element/shade in the same scene while removing the details from the surroundings. It can also be used to extract finer details out of low contrast scenes.
Most modern colour and monochrome negative film sold with ISO marked between 200 and 800 has a wide dynamic range that is close to how we see the world — up to 12~15 stops of light between the black and white points. However, some emulsions, like Adox CMS 20 and many slide film types, have a much narrower dynamic range of about 3~5 stops.
Film exposure is detail — not brightness.
Exposure is just the first step to the complete photographic process. In the darkroom, you can easily make your prints darker or brighter. Your scanner software will auto-adjust the brightness of your image.
The evidence of your exposure’s quality will only be noticeable on the negative itself and in the amount of detail you can get out of it. If you’ve allowed too much light onto your film, you may notice colour shifts and loss of detail in highlights. Too little light will result in noise and grain within shadows, colour shifts, and loss of detail in the dark spots.
Your exposure goal should be to get the maximum amount of detail in the area of most interest within your scene. The final image’s brightness can then be left up to your scanning or printing process.
✪ Note: Instant film combines all the steps of the photographic process into one; in its case, brightness and exposure are the same.
Exposure choices can be subjective.
This article points towards capturing the maximum amount of detail in the area of interest. Following this advice, particularly when combined with a narrow latitude film, can create images that may predominantly look very dark or very bright. Some areas may exhibit a loss of information, but that may not mean an incorrect exposure.
There are cases where the photographer isn’t concerned with preserving all the detail, aiming for a particular effect. As long as they are happy with the results and they match the vision, the exposure is correct.
❤ By the way: if you choose to get your light meter from eBay or Adorama, please consider the above links so that this website may get a small percentage of that sale — at no extra charge for you — thanks!