特殊星由四段組成，每段具有不同的周期數(shù)。因此，可以在聚焦點的良好調(diào)整中將廣角和遠攝位置聚焦。這對于在沒有特殊準直器的情況下定位法蘭焦距非常必要。

此外，西門子星可以是場景的一部分，使得清晰度可以集中在固定點。

The special star consists of four segments each with a different number of cycles. So it is possible to focus the wide angle and the tele position in an optimal adjustment of the focusing point. This is essential for positioning the flange focal distance without a special collimator.

Furthermore the Siemens star can be part of the scene so that the sharpness can be focussed definitely to a fixed point.