Sources - Photography

Now the appropriate film has been selected and inserted into the camera. What should be taken into account when recording? How is the desired result achieved? The correct exposure lays the foundation for high-quality negatives, which can then be processed into positives as often as required.

Expose film correctly

If you always take photos with the same film, the image effect is essentially influenced by the amount of light that hits the photographic material (photography = “drawing with light”). Films are marked with a nominal sensitivity (ISO). If you expose the film according to this sensitivity, you will usually get decent, averagely good results.
Photographic film should always be exposed to the shadows in order to obtain well-drawn negatives. Film is more tolerant of “bleed out highlights” (overexposed bright areas of the image) and therefore behaves in exactly the opposite way to digital sensors, which are more sensitive to too much light. So in practice you would set the desired exposure for the shadows before taking the picture. Of course, this should be done with sensitivity - in situations with high contrast, the darkest areas of the image should not be used for exposure adjustment.

Targeted under- or over-exposure can provide additional creative scope and create a very unique image effect. It is important to know the limits and rules so that you are not surprised by the results. The aim is to fundamentally master the process of creating an image and not to depend on coincidences. Among other things, the graininess of a negative depends on the exposure. With underexposure, only the most sensitive (largest) silver salt grains receive enough light to be developed, so that underexposed negatives are coarser-grained than properly exposed negatives with the same development parameters.

Underexposure or overexposure of the film by up to three f-stops can be compensated for by selecting the development parameters. An underexposed film is developed for a longer time (“PUSH”) and an overexposed film for a shorter time (“PULL”) than intended for the nominal sensitivity.

The chemical processes during development influence the image contrast in PUSH or PULL development:
The blackening of the negative occurs through a chemical reaction of the silver salts to form elemental silver. Where this has already been formed, the chemical reaction occurs more quickly due to catalytic effects. This means that the areas of the negative that have seen more light are developed more quickly than those that have seen less light.

With PUSH development, an underexposed negative is developed. The above-mentioned effects create a negative with significantly higher contrasts. In extreme cases, the shadows and highlights of the finished image converge and detail is lost. At the same time, the graininess of the negative is increased.
If you develop a negative using the PULL method, this has a balancing effect on the contrasts. The overexposed negative also contains latent silver grains in the darker areas, which catalytically accelerate development. The resulting negative has less contrast and is more “flat” with less pronounced graininess. In extreme cases, the negatives are so “thin” that enlargement becomes difficult.

You can make these effects your own by, for example, underexposing an aperture for street photography and then developing PUSH for longer. The negatives and images then become more contrasting and take on a documentary style. A good example here is the Ilford HP5+, which can easily be pushed to ISO 800 with a nominal sensitivity of ISO 400. With a developer that utilizes sensitivity, you get negatives with higher contrast.
For glamor portraits, however, we recommend slight overexposure and PULL development. This results in finer grain, beautiful skin tones and smooth, low-contrast transitions. The best example here would be the Kodak Portra 160, a professional color negative film that achieves the most beautiful results when overexposed to ISO 100 (nominal sensitivity ISO 160).

The exposure metering

For the correct exposure, the amount of light that hits the photographic material must be regulated via aperture and shutter speed. In addition to the film sensitivity, it is also necessary to know the amount of light available in the situation for the selected subject.

SUN 16 rule

If no light meter is available, the amount of light available can be easily estimated using the so-called “SUN 16” rule. It states that in full sunshine and aperture 16, the reciprocal film sensitivity should be used as the shutter speed (e.g. 1/100 s for an ISO 100 film). The less light there is, the more the aperture needs to be opened or the shutter speed increased. Applying this rule good, repeatable results can be achieved, especially outdoors and in simple lighting situations.

Light meter

In more complex lighting situations such as changeable weather, studio shots or street photography, the use of a light meter is recommended. These photometers measure the brightness of the subject so that the aperture number and shutter speed can be calculated.

Photographers have been using photometers since the 19th century. Modern cameras have integrated light meters, which usually measure the amount of light through the lens (through the lens “TTL”). There are also handheld exposure meters. There are now numerous APPS that also provide good measurement results via the camera of a smartphone.

When measuring exposure, a distinction is made between object measurement, i.e. the amount of light reflected or emitted by the object (special case: measurement using a light meter located in the flash unit) and light measurement of the light incident on the object. The latter usually requires a handheld light meter.

Regardless of the above variant, the measurement can be carried out as an integral, spot or multi-field (matrix) measurement. The result provides information about which aperture and shutter speed must be selected in order to expose a subject to a medium gray value (area with a light emission of 18%).

Measuring a purely white area with the light meter results in parameters (shutter speed and aperture) that inevitably lead to a gray area in the finished image. The same would happen with a purely black surface.

Knowledge of  these peculiarities of exposure measurement is important for later image composition. Ideally, you should expose to a spot in the subject that should later appear as a medium gray in the image. Creative use of this knowledge can be used to over- or underexpose certain areas of the image and thus “shift” highlights or shadows. 

This is a list of useful sources on the topics covered in the chapter "Das Foto" dealing with exposure setting and light metering:

Analoge Fotografie - Film richtig belichten

Fotografie in schwarz-weiss - Die richtige Belichtung 

Mein Film Lab - Belichtungsratgeber