An optical system comprising: an optical assembly frame having an input portion and an output portion; an objective lens assembly disposed in a fixed position at the input portion of the optical assembly frame, the objective lens assembly having an objective lens central optical axis; an eyepiece lens assembly disposed in a fixed position at the output portion of the optical assembly frame, the eyepiece lens assembly having an eyepiece lens central optical axis parallel to the objective lens central optical axis and offset from the objective lens central optical axis by a distance (2ΔX); and an image intensifier disposed between the objective lens assembly and the eyepiece lens assembly, the image intensifier having an image intensifier optical axis parallel to the objective lens central optical axis and parallel to the eyepiece lens central optical axis, the image intensifier optical axis being offset from both the objective lens central optical axis and the eyepiece lens central optical axis by half said distance (ΔX); an image intensifier collet disposed around a circumference of the image intensifier and coupled to the optical assembly frame, the collet including a flange extending radially outwardly from the collet and having a plurality of bolt holes spaced equidistantly around the circumference of the flange and corresponding with threaded openings on input portion of frame, wherein the image intensifier comprises an inverting image intensifier, the inverting image intensifier having a fiber optic element that has a 180 degree twist which provides image inversion across image intensifier optical axis, and the image intensifier collet secures the image intensifier to the optical assembly frame, wherein the bolt holes have a diameter larger than that of the bolts to allow adjustment of the collet and image intensifier relative to the objective lens assembly to align the image intensifier optical axis to desired distance from each of eyepiece lens assembly optical axis and objective lens assembly optical axis. an optical assembly frame having an input portion and an output portion; an objective lens assembly disposed in a fixed position at the input portion of the optical assembly frame, the objective lens assembly having an objective lens central optical axis; an eyepiece lens assembly disposed in a fixed position at the output portion of the optical assembly frame, the eyepiece lens assembly having an eyepiece lens central optical axis parallel to the objective lens central optical axis and offset from the objective lens central optical axis by a distance (2ΔX); and an image intensifier disposed between the objective lens assembly and the eyepiece lens assembly, the image intensifier having an image intensifier optical axis parallel to the objective lens central optical axis and parallel to the eyepiece lens central optical axis, the image intensifier optical axis being offset from both the objective lens central optical axis and the eyepiece lens central optical axis by half said distance (ΔX); an image intensifier collet disposed around a circumference of the image intensifier and coupled to the optical assembly frame, the collet including a flange extending radially outwardly from the collet and having a plurality of bolt holes spaced equidistantly around the circumference of the flange and corresponding with threaded openings on input portion of frame, wherein the image intensifier comprises an inverting image intensifier, the inverting image intensifier having a fiber optic element that has a 180 degree twist which provides image inversion across image intensifier optical axis, and the image intensifier collet secures the image intensifier to the optical assembly frame, wherein the bolt holes have a diameter larger than that of the bolts to allow adjustment of the collet and image intensifier relative to the objective lens assembly to align the image intensifier optical axis to desired distance from each of eyepiece lens assembly optical axis and objective lens assembly optical axis.