Levenhuk Ra O-III 1.25 Filter Filter for nebulae observations. Barrel diameter: 1.25 If you don t have the time or opportunity to leave the city to observe a perfectly clear night sky in the countryside don t worry Levenhuk Ra O-III 1.25 Filter is ideal for observation under urban illumination conditions. This filter enhances contrast and reduces light pollution. It s a great accessory for observations of nebulae due to its capability to suppress all light that lies outside its 4900 5010 (490 501nm) passband. This filter can be used for astrophotography as well. Levenhuk Ra O-III 1.25 Filter has a standart barrel diameter so you can use it with a telescope of any brand. Note that this filter gives a green tint to observed objects.