add larger optics on this modularly without a complete disassembly fig4 and 5 show a second embodiment of the night vision system 100 including a compression sleeve 142 that enables a 16 millimeter mm night vision tube to be retrofitted into a housing 102 designed for an 18 mm tube and allowing existing lenses to be retained if desired an advantage of this retrofit is that the 16 mm tube while a non standard tube has a decreased mass relative to the 18 mm tube yet new jumps in resolution allow the 16 mm tube to achieve similar resolution and meet other performance criteria this retrofit is relevant both to legacy devices currently fielded and newer chassis in which the 18 mm is typical in more detail referring to fig4 the compression sleeve 142 has thicker a outer skirt wall 250 in the radial direction than the embodiment of fig1 this added thickness takes up the extra room created by using the smaller 16 mm tube further the front compression buffer 130 has a higher profile b in the longitudinal direction and is integrated with the compression sleeve 142 in this example to form a unitary piece added is an annular or washer shaped rear buffer 154 between the compression sleeve 142 and the rear shoulder 252.