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Antlia H-alpha Pro narrowband filter optimizes the FWHM (full width half maximum) to 3nm bandpass. As the bandwidth becomes narrower, the 3nm Pro narrowband filters enhance contrast of emission targets by lowering the unwanted background signal. Antlia H-alpha 3nm Pro filters are designed to deliver 88% transmission at the 656.3nm line which provides you with the maximum signal and well defined nebulae structures.
Conventional broader narrowband filters cause a heavy loss in transmission due to the strong Center Wavelength (CWL)-shift. We guarantee T>88% within 1nm range of the center bandwidth, which means that the 3nm Pro narrowband filter can guarantee high transmittance for working with both long focal ratios and fast optical systems. Blue-shift data shows that Antlia 3nm Pro filters can be used with nearly all systems as fast as f/3 with minimal loss in emission signal and meets the requirements of fast optics like Hyperstar and RASA.The out of band blocking specification is rated OD5 (0.001%) which delivers an excellent SNR(signal to noise ratio) and effective cut-off rate to minimize interference from other wavelengths. Improved sharp cut-off astrophotography 3nm Pro filters are designed to minimize halos around bright stars.
I purchased a set of Antlia 3nm HA O3 S2 36mm unmounted filters from All Star Telescope about 1 month ago. I haven't had much opportunity to use the filters yet, but I did manage to collect a few Ha images of the Crescent Nebula. Attached is a 600sec image taken with a QHY 268m camera and a Esprit 120mm telescope under the murky skies of Morningside, Alberta. In the past I have used Astrodon filters, but the Antlia filters were much less expensive and so far I'm happy with the performance. Antlia claims out of band blocking at > 5, while the equivalent Astrodon claims blocking at >4. Antlia states Peak Transmission at >88% while Astrodon have a Peak Transmission of >90%. For my level of astrophotography, I doubt these differences will matter. The image is a single Ha, uncalibrated, stretched in MaximDl and Photoshop and saved to a jpeg.
Just recently bought the 7-piece set of LRGB + Ha, Oiii and Sii filters and have had an opportunity to test only the three 3nm narrowband filters. I like them--a lot. I have used the much more expensive Astrodon filters on another setup and would say without having done a careful side-by-side comparison that the Antlia filters I have used so far have performed very well, and deliver great value for the money.
