04/25/2026
🔭 We're putting filters to the test, and sharing the results.
Astronomical narrowband filters - whether for visual use or imaging - are extremely precise devices. Even a typical UHC nebula filter has a bandpass in just the tens of nanometers, and any fault in this measurement can completely compromise its utility. At Farpoint Astro, we’re visual astronomers and imagers ourselves, so we take pride in the high quality of our narrowband filters.
That's why we've launched an ongoing filter testing program - measuring our own filters and competitors' side by side using rigorous optical benchmarks including VEI score, OQI grade, visual SNR, contrast gain, passband integrity, and blocking performance. We’ve recently dug our testing setup out and brought it into the shop, and for the next few months, we’re committed to testing as many filters as possible in the interest of honest comparison between products, including our own line of CXB Astro filters.
Our first comparison is between our original Gen 1/2 "Classic" Oxygen-III filter and our new Gen 3 design. The results were eye-opening, and you can see the full data in the attached image. At first glance, transmission appears identical: Classic 97.1% / vs Gen3 97.5%. Bandwidth (FWHM) is also very similar: Classic 11.96nm / Gen3 11.88nm. But of course, transmission and bandwidth only tell part of the story. Where the two filters truly diverge is in blocking - specifically, what each filter does with light outside the passband.
The classic Lumicon OIII, like many older filters, has a serious problem here. At 739nm, well outside the oxygen-III emission line it's supposed to isolate, it transmits a staggering 96.6% of incoming light. Other light leaks, usually less severe, occur at other wavelengths. All of that unwanted light pours through to your eye or sensor, washing out the faint nebula detail you're trying to see and dramatically reducing contrast.
The Gen 3 tells a completely different story. Its worst leak measures just 0.10% at 421nm - effectively sealing out everything it's supposed to block. This single difference boosts performance considerably: The Gen 3 filter's contrast gain in city skies is over 3× higher (3,409× vs 1,113×), its visual signal-to-noise ratio is nearly 3× better (204.5:1 vs 71.4:1) versus the Gen 1/2.
We'll be publishing more comparisons like this over the coming months, covering a wide range of filters across brands and types.
In the meantime, if this comparison has you thinking about an upgrade, our CXB Astro narrowband filters as well as our Lumicon Gen III UHC and Oxygen-III filters are available now at farpointastro.com. Every filter we sell is one we'd stake our own observing session on - and now you can see exactly why.
Clear skies, and stay tuned
