Antlia 2" ALP-T Dual Band Narrow Band Nebula Filter - S-II and H-Beta, 3.5 nm

Antlia ALP-T Dual Band 3.5 nm Narrow Band Nebula Filter for B/W and Color Cameras

Antlia designed this 3.5 nm dual line-pass filter for one-shot color cameras (OSC), DSLRs and mirrorless system cameras. However, it can also be used as a narrow-band filter for monochrome cameras to save valuable shooting time and produce extremely high-contrast luminance shots, even in moonlight and near cities.

The ALP-T dual-band filter passes red [S II] light (672.4 nm) and blue-green H-beta light (486.1 nm) and blocks all other wavelengths. In particular, the unwanted wavelengths of light pollution and airglow are blocked. This allows you to take deep deep-sky images even in moonlight and from close to the city. The signal-to-noise ratio is greatly increased, allowing you to bring out even the faintest nebulae.

The filter is a significant addition to the popular Antlia ALP-T dual band 3 nm Ha&OIII filter. The combination of these two dual band filters allows extreme narrow-band images with OSC cameras by capturing the spectral data from 4 channels i.e. H-alpha/O-III/S-II/H-beta. The spectrum of these four channels can be separated and recombined into various colour palettes in your post-processing. The resulting images can be used for luminance contrast enhancement of traditional RGB-balanced images or creation of images in various popular false-color palettes such as H-O-Hb, S-H-O, H-S-OHb, H-O-O etc.

Why design S-II and H-beta bands pass instead of O-III and S-II bands?

The filter is dedicated to capture H-beta and [S II] emission lines. We know that [S II] is singly ionized sulfur that emits light in the deep red part of the spectrum, beyond H-alpha, but the contribution of H-beta to emission lines in nebulae is frequently overlooked, even though it is the second most common hydrogen emission after the H-alpha line. Capturing more [O III] will boost the existing signal but does not give more information. However, H-beta has the potential to reveal structures not seen using [OIII]. The design is to capture the H-beta emission line in the certain nebulas that contain some blue spectrum, this cannot be captured by H-alpha, S-II and O-III filters. Greater and richer details will be captured in many nebulae images to achieve results with a superior signal-to-noise ratio.

It is generally accepted that the [O III] signal is a relatively weaker contributor to nebulae images. The O-III bandpass sensitivity is an important consideration for any nebulae filter. Most colour cameras (OSC) use a RGGB Bayer pattern. The allocation of twice as many green pixels as compared to either red or blue pixels enables a much-improved capture of the [O III] signal. Furthermore, higher [O III] signal can be achieved by additional exposure using the Antlia ALP-T Ha&O3 filter, then isolating the GB channels, followed by synthesis of an O-III channel to add into your stack.

In the situation where you may only want to add [S II] to your H-alpha and [O III] data, then it may be preferable to buy one S-II narrowband filter and achieve a cleaner [S II] spectral emission. However, Antlia´s new filter design (SII&Hb) includes the H-beta emission line which provides a distinct improvement in nebulae contrast and improved feature separation in H-beta areas.

The quality features of Antlia narrow band filters at a glance:

High light transmission and smallest bandwidth to maximize contrast.

Special anti-reflective coating reduces halos around bright stars, but slight halos can be visible and are not accepted as reason for returns!

Single substrate to eliminate internal reflections

Usable in light-polluted areas and dark locations

Extends exposure time in moonlight conditions

Antlia narrowband Pro filters can be used with low signal loss down to f/4 systems

All Antlia narrowband filters are blackened at the edges to prevent internal reflections of stray light

Superior optical reliability reduces image post-processing effort

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