The ALP-T dual band 3.5nm SII&Hb filter is a dual narrowband filter, which lets the deep red Sulfur-II 672.4nm and the blue Hydrogen-Beta 486.1nm lines through and is primarily engineered for color cameras to assist astrophotographers taking deep sky images with superior SNR(Signal to Noise Ratio). With an FWHM halfbandwidth designed at 3.5nm and achieving an optical density (OD) of 4.5 on unwanted wavelengths, it works strongly in blocking light pollution, moonlight, and airglow, leding to enhanced contrast in nebulae images by effectively passing the SII and H-beta emission lines signal only.

The main features and application

Passes SII 672.4nm and H-Beta 486.1nm lines

Capturing of the two main emission wavebands in the deep red and blue at the same time

Ultra FWHM 3.5nm design allows for increasing exposure time and capturing detailed nebulae signal

Designed to be used primarily with color cameras to capture cleaner data or used as Luminance filter mono cameras to save imaging time

Recommended to be used with ALP-T Dual Band Ha&OIII filter to create images with better SNR( signal-to-noise) and better isolation between the 4 channels

Suppression of optical density (OD)4.5 on unwanted wavelengths improves SNR( signal-to-noise)

Near IR (NIR) is blocked up to 1100nm

Ideal flat-top and moderate bandpass reducing spectrum downshifts

Recommended to use the filter with optics f-ratios slower than f/4 for best performance, for optics faster than f/4, pre-shifted highspeed version is a better choice

Ion Gun Assisted Deposition of double-sided multi-layer coating technology on the double-sided polished substrate making it the most consistent and accurate light pollution suppression filter

Halo suppression anti-reflective coating is used to minimize halo and internal reflections

Designed to suppress artificial lighting from Bortle scale 1 to Bortle scale 8

Blackened edges of unmounted sizes to minimize internal reflections

Antlia's ever-trusted coating technology makes filter durability very reliable

While primarily designed for use with color cameras, the filter is also highly effective with monochrome cameras to save imaging time

Technical Specifications:

	Sulfur-II	Hydrogen-Beta
FWHM	3.5nm +0.5/-0.5nm	3.5nm +0.5/-0.5nm
CWL (Central Wavelength)	672.4nm	486.1nm
Peak Transmission	90%	85%
Blocking	≥OD4.5 @ 300-1100nm
Filter Thickness	2mm+/-0.05mm
Basic Substrate	Optical, Single / Non-glued substrate
Surface Quality	S/D (scratch/dig)= 60/40 (Refer to MIL-O-13830
Transmitted Wavefront	Lambda/4 or better.
Parallelism	less than 30 arcsec
Filter Ring	2'' (M48*0.75)

Spectrum Curve:

It is a significant addition to the popular Antlia ALP-T dual-band Ha&OIII filter and enables false-color images and narrow-band nebula images using OSC. When capturing data with this filter, the nebulae are recorded with high signal-to-noise ratios and greater contrast than without it.

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

The advanced multi-coatings on Antlia ALP-T dual-band filters effectively isolate the red, Ha line, blue-green, OIII line, deep red SII, and the blue H-beta lines from emission nebulae, with almost total suppression of optical density (OD)4.5 on unwanted wavelengths from light pollution, moonlight, and airglow. The result is that both the ALP-T dual band Ha&OIII version and SII&Hb version create a superior signal-to-noise ratio and better contrast in your OSC images whether used in urban or rural areas, making them excellent choices for astrophotographers aiming to capture high-quality and more detailed celestial images.

When you buy 2 filters of the Ha&OIII version and the SII&H-beta version as a COMBO, you can get them at a better price.

Filter Ring:

2'' (M48*0.75)

Ultra-thin filter cell to minimize vignetting by maximize possible clear aperture

Black Anodized Finish

Laser Engraving No Fading

Not Recommended:

Solar imaging

Night visual observation

Not Permitted:

DO NOT LOOK AT THE SUN WITH THIS FILTER DIRECTLY

Serious eye damage will result if you fail to observe the warning.

Why design SII&Hb bands pass instead of OIII&SII bands?

The filter is dedicated to capture H-beta and SII emission lines. We know that SII 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 OIII 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, SII and OIII 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 OIII signal is a relatively weaker contributor to nebulae images. The OIII 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 OIII signal. Furthermore, higher OIII signal can be achieved by additional exposure using the Antlia ALP-T Ha&OIII filter, then isolating the GB channels, followed by synthesis of an OIII channel to add into your stack.

In the situation where you may only want to add SII to your Ha&OIII data, then it may be preferable to buy one SII narrowband filter and achieve a cleaner SII spectral emission. However, our 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.

Antlia ALP-T Dual Band Ha&OIII filter: Dual band filter with a very narrow passband in OIII and H-alpha to achieve a higher signal-to-noise ratio. The resulting contrast improvement for OSC is impressive.

Antlia ALP-T Dual Band SII&Hb filter: Dual band filter with a very narrow passband in H-beta and S-II. This filter is ideal for increasing contrast of nebulae that emit in the sulfur and H-beta range using OSC. It provides additional feature separation and isolation in Hb areas.