What is exposure compensation?

● Theoretical basis and formula of exposure compensation

Whether it is digital photography or traditional film photography, the light emitted by an object is focused on CCD or film through a lens to make it sensitive, and CCD or film is the photosensitive material. Cameras control the amount of light they feel by controlling the exposure time. To get clear, true and rich photos, we must ensure the accuracy of exposure. Too low or too high will lose a lot of details. In order to express exposure, in photography, people use formulas to describe the brightness of the scene, the sensitivity of photosensitive materials, aperture, shutter and other camera characteristics. This is the exposure formula:

Assuming that the lens aperture number is a, the shutter time is t seconds, the scene brightness is b, and the film sensitivity is s, there is the following formula:

A 2/t = bs/k (note: A 2 is the square of a), where k is a constant, which is called the exposure constant of the camera.

In this formula, there are operations such as multiplication/division/square, aperture A and shutter T contain fractions and decimals, and brightness B is a wide range of values (from tens of nits to tens of thousands of nits) ... This formula is too troublesome to calculate, so in the early 1950s, the United States put forward the APEX system method, using 2 as the base and addition and subtraction operations to turn the above parameters into exponential forms.

In APEX system, make

A 2 = 2 av Average income =6.642 lgA.

1/t = 2 TV =3.32 1 lg( 1/T)

0.3S=2^SV SV=3.32 1 lg0.3*S

B is the brightness of the object AV, TV, SV, BV are the intermediate quantities used to participate in the derivation. Substituting the first formula, the following formula is derived:

2^AV*2^TV=2^BV*2^SV

Obviously, according to the exponential algorithm, there are

AV+TV=BV+SV

So in photography, EV is used to represent the sum of AV+TV or BV+SV.