copy of Filter ANTLIA L model 50.8mm

Everything you need to know about the Antlia H-Beta/O-III filter

The Antlia H-Beta/O-III filter is designed for visual observation of gaseous and planetary nebulae and for astrophotography. The extremely narrow bandwidth of the filter allows maximum contrast to be obtained, even with excellent skies. Sometimes only the use of an O-III filter can distinguish the desired object. In many cases, for instruments larger than 250 mm in diameter, the use of an O-III filter is preferable to the more general UHC filter.

The Antlia H-Beta/O-III filter lets through the 2 Oxygen 3 lines + the more difficult Hydrogen-Beta line. It is designed for planetary nebulae, supernova remnants and certain emission or diffuse nebulae. Here is a non-exhaustive list of objects visible with an OIII filter:

Very few objects emit in the H-Beta line. The Horsehead nebula (IC434) is the best known, but remains difficult to observe. A large-diameter instrument (greater than 300 mm) is recommended, in a very dark sky. The Dentelles du Cygne, Dumbell (M27) and the nebula will be relevant targets. These filters are made of the best glass available on the market.

Transmission curve

This diagram shows the percentage of transmission (ordinates) as a function of the wavelength of incident light (abscissae). 400 nm correspond to deep blue, 520 nm to green and 600 nm to red. The line of ionized hydrogen, the most abundant element in the Universe, is at 656 nm. The blue line marks the transmission curve of the Antlia H-Beta/OIII filter.

Technical specifications:

• Transmittance: > 90% on all 3 lines (OIII 500.7nm / 495.9nm and H-Beta 486.1nm)
• Filter thickness: 2 mm +/- 0,05 mm
• Optical quality: Lambda/4 or better
• Parallelism: Arc less than 30
• Mounting type: 31.75mm thread (M28.5)
• Cell: Aluminum with laser engraving and black anodizing