TS Optics 1.25" Gray Filter
Gray filters are used to reduce image brightness, for example on the moon or on bright planets. This prevents over-illumination effects at the moon and at planets and during daytime observation. The filter is also suitable for double star observations with a particularly bright component.
The adaptation:
The filter is simply screwed onto the 1.25" filter thread of the eyepiece or adapter. With transition adapters, the filter can also be screwed in front of the camera lens (see accessory recommendations).
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 1/100.3 times, i.e. 1/2 (transmission 50%) ND06 - the light is reduced to 1/100.6 times, i.e. 1/4 (transmission 25%) ND09 - the light is reduced to 1/100.9 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:

Due to filter threads on both sides, you can combine the grey filter with 1.25" colour filters, thus you can achieve an increase in contrast and a reduction of brightness.
You can also screw two gray filters together to further adjust and enhance the damping effect.