NEUTRAL DENSITY Filters
Understanding Neutral Density Filters
Neutral Density (ND) lters are designed to reduce transmission evenly
across a portion of a speci c spectrum. ND lters are typically de ned
by their Optical Density (OD) which describes the amount of energy
blocked by the lter. A high optical density value indicates very low
transmission, and low optical density indicates high transmission.
T (% Transmission) = 10-OD x 100%
OD = -log
T
100%
ND lters can be stacked to achieve a custom optical density. To calculate
the nal system OD, simply add the OD of each lter together.
Example 1: What is the transmission if OD 0.3 and OD 1.5 lters are stacked?
ODtotal = 0.3 + 1.5 = 1.8
T = 10-1.8 x 100% = 1.58%
Example 2: How can I build a lter with 0.5% Transmission?
OD = -log (0.5%/100%) = -log(0.005) = 2.3
ODtotal of 2.3 could be created by stacking
OD 0.3 + OD 2.0 or OD 1.0 + OD 1.3.
Neutral Density Filter Types
There are two types of ND lters: re ective and absorptive. Re ective
ND lters consist of thin lm optical coatings, typically metallic, that
have been applied to a glass substrate. The coating can be optimized for
speci c wavelength ranges such as UV-VIS or NIR. The thin lm coating
primarily re ects light back toward the source. Special care should
be taken to ensure the re ected light does not interfere with the system
setup. Absorptive ND lters utilize a glass substrate to absorb light by a
speci c percentage.
TECHSPEC® Refl ective Neutral Density Filters
Optical Density Diameter (mm) Transmission Absorptive Price UV-VIS Price UV-NIR Price VIS Price NIR Price
0.3 25 50.0% #46-212 £33.21 #47-205 £91.84 #88-270 £133.66 #63-386 £113.16 #47-528 £82.82
0.5 25 32.0% #48-089 £33.21 #47-206 £91.84 #88-271 £133.66 #63-387 £113.16 #47-529 £82.82
1.0 25 10.0% #48-090 £33.21 #47-207 £91.84 #88-272 £133.66 #63-390 £113.16 #47-530 £82.82
1.3 25 5.0% #63-463 £33.21 #47-208 £91.84 #88-273 £133.66 #63-391 £113.16 #47-531 £82.82
1.5 25 3.2% #48-091 £33.21 #47-209 £91.84 #88-274 £133.66 #63-392 £113.16 #47-532 £82.82
2.0 25 1.0% #48-092 £33.21 #47-210 £91.84 #88-275 £133.66 #63-393 £113.16 #47-533 £82.82
20 | +44 (0) 1904 788600 Edmund Optics®
EO ADVANTAGE:
• Spectrally Flat Transmission Profi le
• UV, VIS, NIR Versions Available
• Over 750 Filters to Choose From
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