1.survery optical prism. 2. low price. 3. good reputation. Survey Prism,optical prism Ruisen optics can manufacture all kind of ... many universities, research development, military, medical instrument and finance etc.survey prism 1.Material: Bk7 ,B270 or others optical glass2.Dimension ... .1 - 0.5mm 7.Clear aperture: >85% 8.Deviation: <5" survey prism