BFL and Holder Change Unequal Reasons

The reasons for this phenomenon may include: 
The optical designers have carefully optimized and compensated the system to keep overall performance at its best. 
Some of the gains may cancel each other out, resulting in the overall focusing performance is not greatly affected. 
There may be some errors or uncertainties in the measurement or data analysis. 
In general, although the difference between BFL and holder variation may seem contradictory, good focusing performance can still be maintained through the overall design and adjustment of the optical system. This phenomenon may reflect the complexity of the optical design and the fineness of the optimization techniques. Further analysis and understanding of this phenomenon will help to better grasp the design and performance characteristics of optical systems.