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 half-bandwidth 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, leading to enhanced contrast in nebulae images by effectively passing the SII and H-beta emission lines signal only.

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./p>

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 Data:

• FWHM: 3.5nm +0.5/-0.5nm
• CWL (Central Wavelength):
  • Sulfur-II: 672.4nm
  • Hydrogen-Beta: 486.1nm
• Peak Transmission:
  • Sulfur-II: 90%
  • Hydrogen-Beta: 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’’ Mounted (M48*0.75 thread)
• Ultra-thin filter cell to minimize vignetting by maximizing possible clear aperture
• Black Anodized Finish
• Laser Engraving, No Fading

Not Recommended:

• Solar Observing and imaging
• Night visual observation
• DO NOT LOOK AT THE SUN WITH ANTLIA FILTERS. Serious eye damage will result if you fail to observe the warning.