Variable Polarising filter (31.7)

The polarising filter is most commonly used to reduce the light from the Moon, but it is also suitable for the planets, or the Sun with a Herschel prism.

By rotating two polarising filters on top of each other, the intensity of the light passing through them can be varied steplessly over a very wide range. The advantage of this is that you can adjust the intensity of the light to any desired value. Note that you will need two polarizing filters!

In the case of refractors, one filter should be screwed into the zenith mirror and the other into the eyepiece, which can be rotated to change the brightness of the image.

In the case of Newtons, the lower filter can be placed e.g. in the narrowing adapter (size 2") and the upper filter in the eyepiece. In the case of two 31.7mm filters, they can be screwed into each other, or perhaps the lens of our Barlow lens can be screwed into its housing by twisting it out.

A pair of double polarising filters, which are screwed together and can be gently rotated, can be inserted into the eyepiece sleeve and the light transmission can be adjusted continuously from 1 to 30%.

When turning two polarizing filters as a set the reduced light can ben between 1-30%.