Antlia ALP-T Dual Narrowband SII (5nm) & H-b (5nm) Filter for f/3.6 & Slower Telescopes - 2" Mounted
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IMPORTANT: Please read this important note below before buying Antlia narrowband filters. No returns will be accepted for Antlia narrowband filters exhibiting halos around bright stars as disclosed below.
Please note that some users may see halos around bright stars in images made with this filter. Such halos have been observed with filters from other leading manufacturers and in the previous generation of Antlia narrowband filters as well. These halos can be caused and/or made worse by other optical accessories in the imaging train, their relative positions, telescope design/optics, camera, software, or a combination thereof. In general, OIII filters seem to have a higher propensity to show halos compared to H-alpha or S-II filters, but in rare cases the latter filters can also exhibit faint halos around bright stars.
Antlia has made great strides in their coatings to minimize haloing of bright stars, but you may still observe this effect to some degree. See the sample OIII image below of Alnitak (magnitude 1.74) and IC434 in Orion (SkyRover 155mm Apo, ZWO 6200MM-P Camera, 20 min exposure) provided by Antlia. In most cases, haloing will not affect your image unless you have very bright stars in the field of view.
Please note we are unable to accept returns of any Antlia narrowband filters if you do observe this haloing effect in your images.
If you must ensure there are no detectable halos in your images, you may want to consider Astrodon or Chroma narrowband filters instead. These filters, however, cost two to three times as much as Antlia 3nm filters do. Antlia is being honest and upfront. They are the ones telling us about these halos, that their filters are great for the money but still not as good as Astrodon/Chroma, and pointing out that with this full disclosure, they will not accept returns. They are leaving it up to the customer to decide if this is good enough for them or not. We believe that for most imaging applications, Antlia filters continue to offer excellent value for astrophotographers and these continue to be among our top sellers.
Quick Overview
Dual band filter with a very narrow pass band of 5nm 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.
Product Details
The ALP-T dual band 5nm SII&Hb filter is a dual line-pass filter, which lets the deep red Sulfur-II line and the blue Hydrogen-Beta line through and is used with one-shot color (OSC) cameras such as DSLR's or astronomical OSC cameras. It is a significant addition to the popular Antlia ALP-T dual band 5nm 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 greater contrast against the background than without it.
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. Ha/OIII/SII/Hb. 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 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 Hb 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&O3 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 Hb areas.
The advanced multi-coatings on Antlia ALP-T dual band filters effectively isolates 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 5nm Ha&OIII (sold separately) and SII&Hb filter creates a superior signal-to-noise ratio and better contrast in your OSC images.
Application and Performance:
- Passes SII 672.4nm line and H-Beta 486.1nm line
- Engineered specifically for use with DSLR, CMOS, and CCD color cameras
- Ultra FWHM 5nm allows for increasing in exposure time
- Recommended to be used with ALP-T Dual Band 5nm Ha&OIII filter (sold separately) to create images with better signal to noise and better isolation between the 4 channels
- Suppression of optical density (OD) 4.5 on unwanted wavelengths improves signal-to-noise
- Extremely steep bandpass and blackened edges of unmounted sizes to minimize internal reflections
- Ideal flat-top and moderate bandpass reducing spectrum down shifts
- Ion Gun Assisted Deposition coating technology on the double-sided polished substrate making it the most consistent and accurate light pollution suppression filter
- Designed to suppress artificial lighting from Bortle scale 1 to Bortle scale 8
- It can also be used as a narrowband filter for monochrome cameras to save imaging time
- Near IR (NIR) is blocked up to 1100nm
Technical Data:
- Blocking: ≥OD4.5
- Filter Thickness: 2mm+/-0.05mm
Sulfur-II
- FWHM: 5nm
- CWL (Central Wavelength): 672.4nm
- Peak Transmission: 90%
Hydrogen-beta
- FWHM: 5nm
- CWL (Central Wavelength): 486.1nm
- Peak Transmission: 85%
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.
Useful Resources
Filter Cell Specifications
D = Filter Cell Diameter = 50.3mm / 2.0"
T = Total Filter Height = 7.3mm / 0.28"
C = Filter Cell Height (Excluding Male Thread) = 4.9mm / 0.19"
M = Male Thread Length = 2.5mm / 0.09"
F = USABLE Female Filter Thread Length = not threaded
S = Glass Substrate Thickness = 2mm / 0.07"
CA = Clear Aperture = 45mm / 1.77"
Other Information
- Country of Manufacture: China
