There exists on optimal value of magnetic focusingfield and beam voltage, which can minimize the ion noise amplitude.
束电流与束电压确定，存在最佳的磁场使离子噪声幅度最小。
2
In addition, auto-searching in focusingfield is also developed, and successive approximation approach was adopted as a method of auto-searching in this focusing system.
此外文章还讨论了在可调焦范围内进行焦点自动搜索的方法，选用了逐次逼近法来进行本系统自动调焦的控制。
3
Proper focusing is critical at night because small apertures are often impractical — therefore one cannot afford to waste mispositioning the depth of field (see hyperfocal distance).