A frequently asked question at Northern Optics is “how do you fit a Skywatcher light pollution filter to a telescope”. The Skywatcher and many other filters screw on to the telescope eyepiece. There are other ways of connecting a filter, but the eyepiece method is the most popular.
The top image shows the filter has a male thread. Most eyepieces have a female internal thread inside the eyepiece barrel. To connect the filter to the eyepiece, you simply screw the two together, as shown in the lower image.
Once attached, the eyepiece can be used as normal, with the filter not causing any obstruction. Filters and eyepieces are available in 1.25″ or 2″. The example shows a 1.25″ filter and eyepiece.
Note that not all 1.25″ eyepieces have standard thread, and some don,t have a filter thread at all. This is only the case with some budget telescope eyepieces. If in doubt, ask before purchasing.
Click here to buy Skywatcher light pollution filters