SLR cameras have the same shooting settings, the same focal length and so on. But the colors of the items are different. Why is the background getting dark?

The reason is that the sofa said, metering.

But the solution is not what he said. ...

It is normal for the background to change, because it is definitely not the same brightness as the subject you are shooting, and it is often far away.

When the camera shoots a dark object, he will feel that the light is insufficient, so he will adjust it to be brighter, so that the dark object is not dark and the brighter background is brighter. When shooting white, the camera will feel that there is too much light, so on the contrary, the object is not white and the background is dark.

Spot-metering the object and then shooting the result must still be the same, because the camera has a gray tone as the middle value and there is no change. As long as the object is brighter than gray, the camera will feel overexposed, and vice versa.

You can use evaluation to measure light. Then white plus black minus!

When shooting bright objects, increase the exposure through exposure compensation, or decrease the exposure. The specific value depends on the situation, generally around 1.0. The principle is actually the way of camera metering.

Don't mess with metering, it's more troublesome to adjust. Maybe the original beat difference of the landlord is not far away, and it is even worse after a little metering lock ... The spot metering should also adjust the exposure compensation, unless you aim at the medium gray metering and rely on the spot spectrum.