Calculating Proper Exposure w/ Digital

Note this is similar but different from Calculating Proper Exposure w/ Film

Step 1. Take a light reading with your light meter in the highlight areas. Lets say it gives you an EV of 14 (thats typical direct sunlight on a sunny day).

Step 2. Take a light reading with your light meter in the shadow areas. Lets say it gives you an EV of 9 (thats typical shadows on a sunny day).

Step 3. Calculate your shadow bias. We expect digital to be able to recover a range of 3 or 4 stops from shadow (under-exposed) areas. Our shadows measured EV 9 in Step 2. When calculating shadow range we add. So EV 9 + 3 or 4 = EV 12 or 13. 12 or 13 is the max EV we can shoot if we want to recover our shadows without too much noise. The further from the measured EV 9 we get, the more noise we gain and detail we lose. Note, potentially many modern cameras can recover as much as 5 or 6 stops from shadows but it can be extremely noisy. If these shadows are out of focus and you don’t mind using a fair amount of noise reduction, this can be acceptable (depending on taste).

Step 4. Calculate your highlight bias. We expect digital to be able to recover a range of 1 to 2, or maybe 3 stops from highlights depending on ISO and the capabilities of your camera sensor. Our highlight (over-exposed) areas measured EV 14 in Step 1. When calculating highlight range we subtract. So EV 14–1, 2, or 3(risky) stops = EV 11, 12, 13. The further from the measured EV 14 we get, the more detail we lose, typically 1 stop is still excellent with highlights, 2 can be tolerable and 3 very risky most likely some loss. There are plenty of technical articles and videos on dynamic range with details on most camera makes and models. I like dpreview.com.

Step 5. Sum it all up. After our calculations above, we see digital will give us a max range of about 7(safe) to 9(risky) stops, 3, 4, 5 maybe 6 in shadows and 2 maaaybe 3 in highlights. Since our measured EV9 to EV14 is only 5 stops (1EV = 1Stop), we can safely fit all our shadows and highlights into the latitude of the digital and no sacrifice or trickery is necessary. Since highlights can go as low as EV12 safely and shadows can go as high as EV 12 or 13 safely and we know the further we get from the measured value the more detail we lose, we decide to shoot with EV 12 as typically 3 stops of range from shadows is safe and 2 stops of range from highlights is safe enough.

Step 6. Apply the EV value to settings. This is much more complicated, typically calculators can do it for you but I’ll summarize to get you started. 1EV = 1Stop. A EV and Stop are measures of light. Increasing an EV or Stop by +1 doubles the amount of light (x2). So EV 3 is twice as much light as EV 4 and half as much light as EV 2. So EV 1 to EV 4 is 8x more light. 2x2x2. EV is typically used when measuring light or the amount of light. Stops is typically used to describe the difference in light or change in light with regard to exposure settings on your camera, though the two are interchangeable. So we would say, something like this: “Going from EV 1 to EV 4 gives us 3 Stops of additional light or 8x more light.” Now to give you a starting place to use this knowledge: F/1.0 at ISO 100 at 1s exposure = EV 0. When we change the aperture by 1 stop to F/1.4 at ISO 100 at 1s, EV = 1.

Here’s an example table all in ISO 100:

Horizontally we have the Aperture F-number (light and depth of field)

Vertically we have the EV number (amount of light, measured)

Diagonally we have the shutter speed (light and duration of exposure)