How to calculate light ratio in photography?

The first level of light ratio represents the double difference of light input, which is absolutely correct.

For example, if the aperture is enlarged by one level, or the exposure time is doubled, or the ISO is doubled, the light input can be doubled, that is, the exposure is+1 level, which is easy to understand.

As for what formula to add, it is absolutely wrong. Take a very simple example to refute, the difference between two photos exposed to 1 s and two seconds is obviously twice, because two photos exposed to 1 s can be changed into two photos exposed to two seconds. For another example, turn on the tap and connect the water with a cup. The water received in 2 seconds is obviously twice as much as that received in 1 second. As for the calculation formula, I don't know who made it up. I've never heard of it. 1/3 of 1000 is equal to 1/3 of 100? How can inequality communicate at the same level?

Say that stupid formula again, difference 1:3, difference 1: 4. Then just change the aperture to one level and add an ISO maintenance 1: 3 to make this ISO value a1; On the other hand, the poor level 3 is 1:5, and the poor level 4 is 1: 6. I use an ISO to maintain 1: 5. Let the ISO grade be a2, then a 1 is not equal to a2, and so is ISO 100 to 200.

As for the aperture number, the aperture coefficient = [lens focal length]/[entrance pupil diameter] = f/d, which is not clear. You can check the aperture coefficient in Baidu Encyclopedia.

The concept of 1 times phase difference is reflected in the fact that the area of the entrance hole is two times different, which is also easy to understand.

For example, for a 50mm lens, the maximum aperture is 25mm, so the maximum aperture =50/25=2.0.

In practice, you can adjust the style of photos by increasing or decreasing the aperture, shutter speed and ISO (adding one level and subtracting another). If you don't know the concept of depth of field very well, I'll say it by the way.

11000sf2.8 and115SF22 have the same picture brightness, so what's the difference? Just try it. The background of f2.8 is vague, while the foreground and background of f22 are basically clear. The larger the aperture, the smaller the depth of field. We control the depth of field by changing the aperture and shutter value.

At the same time, the closer the camera is to the subject, the smaller the depth of field; The greater the focal length of the lens, the smaller the depth of field.

I'm tired of typing.