In the 80’s, everyone was just using the term exposure latitude when talking about film. Until the age of digital, I began to hear people talking about dynamic range of the digital sensor. The meaning of these two terms seem to be the same but in my opinion, they may be totally different.

According to Ansel Adam, a typical outdoor scene containing sky and ground will have approximately 7 – 7.5 stops differences in tonal range, i.e., from Zone II to Zone VIII. For example, a white cloud in the sky lit by the sun will be in Zone VIII and a piece of dark rock on the ground in shade will be in Zone II.

The term “Dynamic Range” is used to describe the capturing medium – either film or digital sensor, its ability to record the brightness range of a scene with useful image texture/detail information, before image is completely black or white.

In modern color negative film, the dynamic range is about 12 stops. When a 7.5 stops brightness range image is correctly exposed at the mid portion of the curve as below, there will be about -2 stops underexposure latitude and +3 stops overexposure latitude. So we say the film has an “exposure latitude” of about +/- 2.5 stops.

Negative Film

For reversal film, the dynamic range is much narrower so the exposure latitude is only +/- 1/2 stop as below:

Reversal Film

To illustrate with a real life example, a car 7 feet wide (scene brightness range of 7 stops) is driving through a door of 12 feet wide (dynamic range of 12 stops). The driver (photographer) will have an error margin (exposure latitude) of left/right 2.5 feet (+/- 2.5 stops) if he correctly drive his car in the middle(correctly expose the image), without hitting the left or right edge of the door and damage his car(under/over expose the image).

Dynamic range is commonly used for digital camera sensor nowadays. I have seen that recent digital cameras have dynamic range of 14-16 stops.

In 00’s when digital camera was getting the attention in the motion picture market, I had heard a cinematographer saying that a 13 stops dynamic range of a new digital camera at that time was able to have an exposure latitude of +/- 6.5 stops (13 stops divided by 2), so he claimed that he would not need the light meter anymore!

Of course, this is totally misleading.

If the scene he shot only contain one tone, e.g., a grey card filling the whole frame, his statement may be correct and he could over- or under- exposed the grey card by 6.5 stops and the camera can still record the image properly. For a normal scene of 7.5 stops brightness range, the exposure latitude of this camera was only +/- 2.75 stops so accurate light metering was still necessary.

In film age, “exposure latitude” was used sometimes to describe the dynamic range of a film. Now we have the term “dynamic range” from digital age so we can separate the use of “Dynamic Range” and “Exposure Latitude” in different meaning to avoid confusion.

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