Abstract: An optical device for an intensifier tube having an elongated housing with a cylindrical chamber extending therethrough, an intensifier tube in said chamber, first and second annular means in said chamber. Fastener means in said housing for releasably fixing said first and second annular means in selective axial position in said housing whereby the axial mounting position of the intensifier tube may be varied. Objective and eye piece optical means for projecting light to and receiving light from the intensifier tube.Third and fourth annular means in said housing. The third annular means positioned in said chamber at one end of said housing, and the fourth annular means positioned in said chamber at the other end of said housing. The intensifier tube and said first and second annular means are positioned between said third and fourth annular means. Connector means on each of said third and fourth annular means for connecting to said objective and eye piece optical means.