I've noticed that camera's focal length and viewport's focal lengths don't match. I agree with the Alessandro Padovani (padone) who created the parent task.
Basically, when you have a scene and want to do a quick test render of what you see in the viewport you need to set the camera's position/rotation to viewport's view. To do that you first view the scene using the viewport then set the camera's position/rotation using Ctrl+Alt+0 (numpad) and hit F12. The problem with this is viewport's focal length and camera's focal length don't match even though they are both set to 50mm.
When you hit Ctrl+Alt+0, camera's position/rotation is set but what camera sees is actually zoomed in which seems like 100mm. So, if you want the camera to see what the viewport sees then you need to change viewport focal length to twice of what camera is.
I don't know what the parent task was closed.
I'm using Blender 2.90
Build date: 2020-06-23