Calibration

Fenn Night Vision Goggles should be returned to the company every year for the following maintenance procedures:

  • Inspection to ensure no mechanical parts are damaged or missing
  • Check for free movement of all adjustable parts
  • Check to ensure release levers operate without hesitation or binding
  • Check performance at high and low light levels
  • Check resolution
  • Check and set the dioptre scale
  • Gain test on each monocular to ensure these meet an acceptable standard and do not differ by more than a set percentage
  • Image distortion test on each monocular to verify that a grid pattern of perfect squares appears uniform in size with all lines appear to be perfectly straight

An image quality defect test will be carried out on each monocular to identify:

 

a)         Spot defects

b)         Bright spots

c)         Emission points

d)         Flashing, flickering or intermittent operation

e)         Fixed pattern noise (characterised by a faint hexagonal pattern in the viewed screen)

f)          ‘Chicken wire’ (an irregular pattern of dark thin lines in the viewed screen)

g)         Grain boundary growth (an irregular pattern of dark thin lines in the viewed screen)

 

If the defects a to g are above acceptable limits, the image intensifier will need to be replaced.

 

h)         Shading ( a dark area along the outer edge of the image)

i)          Edge glow (a bright area along the outer edge of the image)

 

If h and i are evident, the image intensifier will need to be replaced.

  •  Check zero dioptre setting and dioptre range
  • Check and reset collimation, (this is necessary whenever alignment of the optical components is disturbed by other maintenance)
  • Purge the volume within the monocular housing with dry nitrogen

Following annual calibration, overhaul or repair, the product warranty will be extended for a further 12 months.  Please note, image intensifier tubes are excluded from this extended warranty.