TS Optics 2" Gray Filter ND09 - 12.5% transmission
This neutral-density filter or gray filter reduces the brightness to 1/8 without colouring the image, preventing haze effects at moon and planets. The filter is also helpful for observing double stars with one particularly bright component.
The filter is suitable for daytime observing, too, as the light attenuation increases the perception of fine details. Thtough the high absorption of ND09, a strong brightness reduction is achieved.
For solar observation, an additional solar filter
in front of the lens has to be used. The filter effect of all common neutral density filters is far too weak, leading to serious eye damage.
Photographic use:
Particularly in daytime photography or solar photography (only with front solar filter), light attenuation is often desired. Even the shortest exposure time of the camera makes the image to appear too bright. With certain DSLR cameras, the shutter can be seen as shadow at the edge of the image. By using the grey filter, the exposure time is extended and the effect is prevented.
The adaptation:
The filter is simply screwed into the 2" filter thread of the eyepiece or the adapter. With a suitable adapter, the filter can also be mounted in front of a camera lens (see recommended accessories).
What does the ND value mean:
The ND value provides information about the attenuation factor. The higher the value, the stronger the attenuation factor. However, there are two versions:
1. Logarithmic scaleThis is used with our older gray filters, but also for solar filter foil. The transmission is calculated here as 1/10
ND, whereby the ND value may have to be provided with a comma:
♦ ND03 - the light is reduced to 1/10
0.3 times, i.e. 1/2 (transmission 50%)
♦ ND06 - the light is reduced to 1/10
0.6 times, i.e. 1/4 (transmission 25%)
♦ ND09 - the light is reduced to 1/10
0.9 times, i.e. 1/8 (transmission 12.5%)
Advantages are the large range and the possibility to easily add the ND values of combined filters.
2. Linear scaleThis is used with our newer gray filters. The transmission is simply calculated according to 1/ND:
♦ ND16 - reduction by 16 times - light transmission is 6.25%
♦ ND32 - reduction by 32 times - light transmission is 3.13%
♦ ND64 - reduction by 64 times - light transmission is 1.56%
The advantages are the simple calculation of the attenuation by individual filters and thus the direct calculation of the extension of exposure times.
Practical tip from Teleskop Service:
By using the threads on both sides, you can combine the gray filter with 2" colour filters, so you can achieve contrast enhancement and brightness attenuation.
You can slso screw two gray filters together for increasing the damping effect.
