The O-III filter operates in the area of ••two lines of double ionized oxygen, corresponding to 496 and 501 nm. It is an in-bandy filter designed for shooting many gas nebulae and planetary nebulae. The most interesting objects that are photographed in the O-III band are Veil in Łabędziu, Laguna (M8), Omega (M17), Pier¶ (M57), Dumbells (M29).
The filter is suitable for telescopes with a minimum diameter of 90 mm.
The difference between UHC and O-III filters
O-III filters do not replace UHC filters. They are stronger than UHC filters, they increase the contrast dramatically, but they greatly reduce the brightness of other objects and even eliminate weaker stars, simultaneously increasing the detail of the observed object characterized by the presence of the O line. -III.
(measurements on the Varian Cary 100 spectrophotometer, July 2015)
Connection of ALL astronomical filters with the exception of solar film filters (which are filters for the lens) is accomplished by screwing the filter into the frame of the eyepiece from the opposite side than applying the eye (ie from the side that we put in the eyepiece extractor) . The filters can be additionally connected with each other, because they have threads on both sides of the luminaire.