How to explain "actual focus, effective focus and standard focus" in medical images?

Focus is an important factor in X-ray photography. The so-called focus is the intersection of extension lines opposite to the main X-ray irradiation direction. The ideal focus is a point, which actually has a certain area. Focusing can be divided into actual focusing and effective focusing from different angles.

1. The actual focus is the region where the electrons emitted by the cathode lamp line hit the anode target at high speed. The thinner the electron beam, the smaller the area hitting the anode target surface and the clearer the image.

2. Effective focus The effective focus is the projection of the actual focus in the X-ray irradiation direction. Because the anode target surface is an inclined plane with a certain angle, in the direction of X-ray photography, it is the sine value of the actual focus that affects the imaging. Generally, the values of1.0,2.0 marked by X-ray tubes are the nominal values of their effective focus.