The Diagonal Eyepiece is used for use in areas where large building or obstacles prevent an ideal working distance between the Theodolite and target object. The Solar Filter is used on the Theodolite to prevent glare under bright sunlit conditions, or when the sun must be sighted to determine position.
The CST/Berger DGT10, BDT30, and David White DWT-10(46-8890), DWT-30(46-8895) are all able to utilize the 56-DTEP Diagonal Eyepiece.