How to avoid the grid focus deviation and the focal length does not match?

It is inevitable that the center deviation of the grid and the focal length do not match, but this feature of the grid is regulated.
The center deviation of the grid should be avoided as much as possible. In the case of a stationary grid, there should be no deviation; when using an active grid, a center deviation will inevitably occur, but the amount of deviation should be designed to be as small as possible.

In some cases, depending on the location of the exposure, the distance from the focus to the cassette needs to be changed, but the grid cannot be replaced frequently, so only one focal length change can be specified as the original emission line at the edge of the effective area of the grid. When the transmittance is reduced by 40%, the distance of the glue at this time is generally defined, and the change of the film distance should be no more than or less than 25% of the focal length of the filter. Therefore, the focal length indicated on the grid is the nominal focal length, and the actual usable focal length has a certain range.

Author：Alina