98 • Additional Reference Information Genie Nano-CL Series™Back Focal Variance when using any FilterInserting a filter between a lens and sensor changes the back focal point of the lens used. Avariable focus lens simply needs to be adjusted, but in the case of a fixed focus lens, the changedfocal point needs correction.The following simplified illustration describes this but omits any discussion of the Optics, Physics,and the math behind the refraction of light through glass filter media.sensor surface(focal plane)Focal Point withfilter is behindsensor surfaceFilterIllustration: Change of FocalPoint with inserted filterIncident Light(from Lens)In this example when a glass filter is inserted between the lens and the camera sensor, the focalpoint is now about 1/3 of the filter thickness behind the sensor plane. Genie Nano filters arespecified as 1mm thick.Genie Nano models with factory installed filters automatically compensate for the focal pointvariance by having the sensor PCB mounted deeper within the camera body.For Nano models normally shipped without filters, when a filter is installed a fixed focus lensrequires a 1/3mm C-mount shim (spacer) added to move the lens focal point back to the sensorsurface. Such shims are available from filter and lens suppliers. Alternatively use a variable focuslens and secure its focus ring after adjustment.
