Digital cameras automatically calculate exposure. For many film cameras lacking a built-in light meter, however, an alternative method is necessary to determine the correct exposure. Could a simple estimation be a viable approach?
Just as guessing the weight of a basket of groceries is made easier by common experiences—like routinely lifting a one-liter water bottle—we can apply a similar estimation game to light measurement. The question is: How can we estimate the correct exposure for film or a digital sensor purely by observing the light? While this might seem unnecessary given the sophistication of built-in spot meters in modern cameras, this practice is valuable for several reasons.
Taming the light
Even when discussing the technicalities of adjusting ISO, shutter speed, and aperture, we can start with a philosophical parallel. The painter Georges Braque (1882-1963) often recommended Eugen Herrigel’s book, Zen in the Art of Archery, even giving a copy to Henri Cartier-Bresson (1908-2004), who found it a revelation. Herrigel (1884–1955) was a student of the Japanese master archer Awa Kenzo (1880–1939). Awa Kenzo taught that in life, as in archery, the archer, the bow, the arrow, and the target are fundamentally a single entity.
We can apply this concept directly to photography: the photographer, the light, the camera, and the subject are one. While we may rely on the light meter for automatic exposure, correctly guessing the exposure becomes an integral part of the creative process. To evaluate the right exposure by eye is to anticipate the perfect blend of aperture, shutter speed, and sensitivity. It represents the profound feeling of unity with the very moment the photograph is captured.
f/16 rule
A foundational principle for determining exposure based on visual observation, essential knowledge for any photographer, is the f/16 rule. This rule states that on a bright, sunny day, within the period of two hours after sunrise and two hours before sunset, a correct exposure for a subject or scene with average values directly illuminated by the sun can be achieved with a shutter speed of 1/ISO seconds at an aperture of f/16.
For instance, with an ISO setting of 125, the suggested exposure is 1/125 s at f/16, or any equivalent combination of aperture and shutter speed. This baseline exposure of 1/ISO s at f/16 has historically been the standard used by film manufacturers to create the exposure tables in their technical manuals, and it is even inscribed on the back of the body of certain cameras, such as many Rolleiflex models.
Shutter speed adaptation
For film cameras, where the film sensitivity (ISO) rarely aligns exactly with available shutter speeds, select the closest speed. For instance, use 1/125 s or 1/60 s for 100 ISO film, or 1/500 s or 1/250 s for 400 ISO. With film, especially negative film, it is generally safer to slightly overexpose than to underexpose.
This issue of matching ISO and shutter speed is absent in digital photography. Digital cameras allow shutter speeds to be adjusted in ⅓ EV increments, mirroring the progression of ISO settings. Furthermore, shooting in Raw format provides greater exposure latitude.
Training with EXIF data
EXIF data in digital photography provides a post-shot method for checking the accuracy of the “1/ISO second at f/16” exposure rule. Reviewing this shooting information in software like Lightroom aids in developing a photographer’s exposure judgment.
Compensations
When the sky is overcast or the sun is slightly obscured, you will need to compensate for the reduced light. The following table, summarizing necessary exposure adjustments based on light intensity variations, is derived from film manufacturers’ recommendations and is entirely applicable to digital photography. EV (Exposure Value) explained: ± 1 EV corresponds to a change of one stop, for instance, shifting the shutter speed from 1/125 s to 1/60 s or to 1/250 s.
| Exposure guide without a light meter, outdoor subject | ||
|---|---|---|
| Lighting conditions | Subject | Exposure |
| Bright sun, sharp shadows | Average reflectance, front-lighting | 1/ISO at f/16 |
| Bright sun, sharp shadows | High reflectance (light-colored sand, foamy sea, snow), front-lighting | -1 EV |
| Bright sun, sharp shadows | Average reflectance, side-lighting | +1 EV |
| Overcast sun, soft shadows | Average reflectance | +1 EV |
| Light cloud cover (without pronounced shadows) | Réflectance moyenne | +2 EV |
| Dark cloudy (without marked shadows). Open shade | Average reflectance | +3 EV |
When photographing a subject with high reflectivity (such as light-colored sand, foam, or snow) in direct sunlight with front lighting, a -1 EV exposure compensation is required. Using a Nikon D850 with a 50mm lens, the correct exposure for ISO 400 is 1/800 s at f/16. To achieve the equivalent exposure, the camera is set to 1/3200 s at f/8.
With the sun still direct but offering lateral lighting, a +1 EV compensation is applied. This setting—1/200 s at f/16 for ISO 400—is necessary to prevent underexposure in the shadows while retaining highlight detail. The camera setup (Nikon Df, 24-70 mm) uses an equivalent combination of 1/3200 s, f/8.
When the sky is overcast, resulting in diffused, soft shadows, applying a +1 EV exposure compensation effectively offsets the decreased luminance caused by the cloud cover. This standard exposure is equivalent to 1/100 second at f/16 with an ISO of 200. The settings used on the camera (an Olympus E-M1 with a 12-45mm lens) were equivalent to 1/800 second at f/5.6.
Under a clear, yet cloudy sky, outdoors, the light is naturally diffuse, meaning there are no sharp shadows. To compensate for the reduced luminance caused by the clouds, a +2 EV adjustment is necessary. This compensation results in an exposure of 1/50 s at f/16 with an ISO of 200. The camera used (Olympus E-M1 with a 12-45 mm lens) was actually set to 1/800 s at f/4.
For scenes under dark clouds or in open shade (such as the shady side of a narrow street on a sunny day), the exposure needs an adjustment of +3 EV relative to the “1/ISO rule at f/16.” For example, with ISO 400, this equates to a base exposure of 1/50 s at f/16. The specific camera settings used on the Olympus E-M5 (with a 12-50 mm lens) were 1/200 s at f/8.
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Text and photos: Philippe Bachelier, teacher of Printing techniques at Spéos