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These filters possess level spectral transmittance characteristics in the visible region and attenuate light by absorption with minimal reflection. Typically, neutrality and density of absorptive filters are a function of the material and the thickness. Since Hoya neutral density filters are held to a specific optical density, the thickness is only a function of the glass type. They are useful in light control applications for measuring instruments and exposure control in imaging. Spectral variations occur as optical density increases.
Optical Density exhibits an additive relationship; for example, stacking filters with OD values of 0.6 and 0.9 yields a resultant density of 1.5. The optical density is related to the transmission by the following equation: T = 10^-OD x 100 = percent transmission.
#55-222 includes 6 filters in optical density values of 0.15, 0.3, 0.4, 0.6, 0.9 and 2.5. Wooden Box with foam lining included.
#63-468, #63-469, #63-470 and #66-155 each include 14 filters in optical density values of 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.9, 1.0, 1.3, 1.5, 2.0 and 2.5. Please note that OD 3.0 is the only one not included in these kits. Wooden Box with foam lining included.