| Substrate Material: |
Absorptive optical glass, neutral density type
(vision light) |
| Outer Dimension: |
Dia 25.4,-0.2, +0.0mm |
| Surface Quality: |
Double side optical polished, 60-40 S/D |
| Optical Density Tolerance: |
< +/-5% @ 546nm |
| Accessory: |
Mounted (outer diameter 30mm; L12mm type; SM10 inner thread c/w retailing ring); Compatible to standard Thorlabs SM10 parts. Black anodized. |
Optical Density:
OD = Log10 (1/T) or T = 10OD |
| OD=0.04 |
T=92% |
+/-2% |
| OD=0.1 |
T=79% |
+/-2% |
| OD=0.2 |
T=63% |
+/-2% |
| OD=0.3 |
T=50% |
+/-2% |
| OD=0.4 |
T=40% |
+/-2% |
| OD=0.5 |
T=32% |
+/-2% |
| OD=0.6 |
T=25% |
+/-2% |
| OD=0.8 |
T=16% |
+/-2% |
| OD=1.0 |
T=10% |
+/-2% |
| OD=1.3 |
T=5% |
+/-2% |
| OD=2.0 |
T=1.0% |
+/-2% |
| OD=3.0 |
T=0.1% |
+/-2% |
| OD=4.0 |
T=0.01% |
+/-2% |
| OD=5.0 |
T=0.001% |
+/-2% | |
For a ND filter with optical density d the amount of optical power transmitted through the filter is given by:
Fractional Transmittance = 10-d
For example, on a very bright day, one might wish to photograph a waterfall at a slow shutter speed to create a deliberate motion blur effect. In order to do this, one would need a shutter speed on the order of tenths of a second. There might be so much light that even at minimum film speed and a minimum aperture such as f/32, the corresponding shutter speed would still be too fast. In this situation, by applying an appropriate neutral density filter one or more stops can be taken out of the exposure, allowing a slow shutter speed and motion blurred effect. An ND filter can also be used to create motion blur, if the photographer closes the aperture to a diameter such as f/32, as extremely small apertures tend to require slower shutter speeds. They also soften the image due to diffraction.
The use of an ND filter allows the photographer to utilize a larger aperture that is at or below the diffraction limit, which varies depending on the size of the sensory medium (film or digital) and for many cameras, is between f/8 and f/11, with smaller sensory medium sizes needing larger sized apertures, and larger ones able to use smaller apertures. With using ND filters to limit the light instead of the aperture, the photographer can then set the shutter speed according to the particular motion desired (blur of water movement, for example) and the aperture set for maximum sharpness. Using a digital camera, which provides results right away, a photographer could find the right ND filter to use for the scene being captured by first knowing the best aperture to use for maximum sharpness desired. The shutter speed would be selected by finding the desired blur from subject movement. The camera would be set up for these in manual mode, and then the overall exposure then adjusted darker by adjusting either aperture or shutter speed, noting the number of stops needed to bring the exposure to that which is desired. That offset would then be the amount of stop needed in the ND filter to use for that scene.
Another use of neutral density filters is in controlling exposure with mirror-lenses catadioptric optics, since the use of a traditional iris diaphragm increases the ratio of the central obstruction found in those systems leading to poor performance.
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Optical Substrates
