Antlia 7nm Narrowband SII Prime Filter

A 7nm Bandpass with >90% Peak Transmission

This filter centers its 7nm bandpass on 672.4nm to capture the deep red light of ionized sulfur, with high transmission at the SII emission lines at 671.6nm and 673.1nm. Antlia says this ensures maximum signal strength and well-defined nebular structures.

OD4 Blocking and Minimized Star Halos

Effective narrowband imaging depends on rejecting all light outside the target wavelength. The 7nm Prime filter provides OD4 blocking, suppressing more than 99.99% of out-of-band light from 300-1000nm, which Antlia says delivers an excellent signal-to-noise ratio and better contrast, in light-polluted areas and at dark sites. The filter is built on a single, non-glued optical substrate to eliminate internal reflections, its edges are blackened against stray-light reflections, and its steep spectral profile minimizes halos around bright stars.

Signal Integrity on Systems as Fast as f/2

Using narrowband filters on fast optical systems introduces a steep light cone that can shift a filter's bandpass. Antlia states that, with their wider FWHM, 7nm Prime filters can be used with nearly all systems as fast as f/2 with minimal loss in emission signal.

Antlia 7nm Prime vs. 3nm Pro: When to Choose a Wider Bandpass

Antlia offers both 7nm Prime and 3nm Pro series filters, each with distinct advantages. The choice depends on your equipment and observing site.

• Choose the 7nm Prime if: You use a very fast optical system (f/4 or faster), where the wider bandpass is more forgiving of band-shifting. It also gathers signal more quickly, which can be an advantage for shorter imaging sessions.
• Choose the 3nm Pro if: Your primary goal is maximum contrast, especially from heavily light-polluted locations. The tighter bandpass rejects more background skyglow but requires longer exposure times. Antlia rates the 3nm Pro series as usable down to f/3.