About this product
Model: antlia_ha_3nm_31mm
Part Number: H-alpha 3nm Pro 31mm
Antlia 3nm H-alpha / Ha Pro Astronomy Filter
Antlia H-alpha Pro narrowband filter optimise the FWHM (full width half maximum) to 3nm bandpass. As the bandwidth becomes narrower, the 3nm Pro narrowband filters enhance contrast of emission targets by lowering the unwanted background signal. Antlia H-alpha 3nm Pro filters are designed to deliver 88% transmission at the 656.3nm line which provides you with the maximum signal and well defined nebulae structures.
Conventional broader narrowband filters cause a heavy loss in transmission due to the strong Centre Wavelength (CWL)-shift. Antlia guarantee T>88% within 1nm range of the center bandwidth, which means that the 3nm Pro narrowband filter can guarantee high transmittance for working with both long focal ratios and fast optical systems. Blue-shift data shows that Antlia 3nm Pro filters can be used with nearly all systems as fast as f/3 with minimal loss in emission signal and meets the requirements of fast optics like Hyperstar and RASA.
The out of band blocking specification is rated OD5 (0.001%) which delivers an excellent SNR (signal to noise ratio) and effective cut-off rate to minimise interference from other wavelengths. Improved sharp cut-off astrophotography 3nm Pro filters are designed to minimise halos around bright stars.
IMPORTANT: These filters are NOT designed for observing or photographing the Sun. DO NOT use these filters to observe or photograph the Sun. If you do it will result in permanent eye damage!
FEATURES
- 3nm FWHM Ha filter - 656.3nm centre wavelength
- High transmittance and smallest bandwidth to maximise contrast
- Steep spectral profile minimises halos around bright stars
- Suitable for imaging narrowband objects: H-alpha Emission Nebulae, Planetary, Wolf Rayet Nebulae and Supernova Remnants
- Use in light polluted areas and dark sites
- Extends imaging time when the moon is up
- Suitable for fast systems down to f/3 without loss of signal
- Edge blackened to eliminate internal reflections from stray light
- 2mm+/-0.05mm thickness for 1.25", 2" mounted, 31mm and 36mm unmounted
- 3mm+/-0.05mm thickness for 50mm and 50x50mm unmounted
- Fine-optically polished on both sides
Transmission Chart
Blue Line - Represents the transmission curve of the filter.
The Major Emission Lines of Nebulae: H-α (656.3nm), H-β (486.1nm), OIII (495.9nm) and OIII (500.7nm)
The Major Emission Lines of Artificial Light Pollution: Hg / Mercury (435.8nm, 546.1nm, 577nm and 578.1nm), Na / Sodium (598nm, 589.6nm, 615.4nm and 616.1nm)
Specifications
Basic Substrate: Schott optical substrate
Filter Thickness:
2mm+/-0.05mm for 1.25", 2" mounted, 31mm and 36mm unmounted
3mm+/-0.05mm for 50mm and 50x50mm unmounted
FWHM (Full width at half maximum): 3nm
CWL (Central Wavelength): 656.3nmnm
Peak Transmission: >88%
Blocking: > 5 OD(0.001% out of band blocking) @ 300-1000nm
Surface Quality: S/D (scratch/dig)= 60/40 (Refer to MIL-O-13830)
Transmitted Wavefront: Lambda/4 or better.
Parallelism: less than 30 arcsec
Single / Non-glued substrate
Filter Ring:
1.25’’(M28.5*0.6) or 2’’(M48*0.75)
Ultra-thin filter cell to minimise vignetting
Black anodised finish Laser engraving
No fading
Customer reviews
Average Rating (1 Review): | |
Optical Filters having a 3 nm bandwidth 15 November 2023 | Ian
Owing to difficult sky conditions, only one session has been possible with the 3 nm filters installed. Below are some notes that I made primarilly for myself, but I am happy to share these with you. There are two other issues that I would wish to comment on, and your response would be appreciated:
1. The physical outer diameter of the filter housing seems to be slightly larger than the Baader ones that are being replaced, this has meant that it has not been possible to fully screw them into the filter carousel - especially the Halpha one.
2. I carry out fine focusing using a wide-band IR/UV filter, and assume that the characteristics of the narrowband filters are identical. On examining my raw images collected, I feel as though the focus is just a tiny bit off. Could it be that there is some variation of substrate between manufacturers? Carrying out fine focusing through a narrowband filter will take a good while, which I would wish to avoid.
Initial Comparison of 3nm and 7nm Optical Filters
These notes refer to imaging of the object NGC7023 using the Hɑ 3 nm optical filter in a 1.25 inch format. (This filter and the two others were purchased from FLO, order PO261345). The telescope is a 1200mm F4.7 Newtonian having a Baader Mark-III MPCC Coma Corrector (Also purchased from FLO). The exposure duration was 300 seconds per raw image, and guidance was controlled by the PhD Mk2 software, and over a period of 3 hours - the RMS error for the duration on both axes was 0.8 arc-seconds.
Two sessions using the same target were executed during which 10 raw images were collected for the original 7 nm filter, and then 10 images using the new 3 nm filter Antlia 3nm H-alpha Pro Astronomy Filter. The optical train was unchanged, save for the filter substitution. The camera was an ASI 1600MM PRO with the sensor cooled to -20° C.
To establish the gain from using the 3 nm filter, specific measurements were made on one raw image selected from the middle of each set. The following parameters were obtained using Pixinsight 1.8.9-2:
(all values are x10E-2) 7 nm filter 3nm filter
(a) Mean of entire raw image 2.93 1.30
(b) Mean of a small non-star region (background) 3.06 1.25
(c) Mean of a small region of nebulosity 5.42 3.40
There is literature that sets out the typical spectral distribution of the current generation of LED street illumination, and it shows that the spectral density is fairly uniform across the visible band. I strongly believe it is the scattering of this source that constitutes the predominant background interference at the location of my observatory. This locality is classed as Bortle 6, and is the main reason for investing in the 3nm filter set – the 7 nm set which I have used for many years has not delivered satisfactory images at this location. Consequent;y it seems not unreasonable to expect that the “noise” component of my images to be reduced in the ratio of the respective bandwidths i.e. 7:3 or 2.33 times. Looking at (b) above we see that the measured ratio of the background noise is 2.45. This seems pretty close to expectation.
We can make a further deduction from the data above, on the basis that the background (b) could well be added to those regions where a wanted signal exists, for example, the nebulosity. If the background (c) is subtracted from the nebulosity signal (c), we obtain an estimate of the uncontaminated wanted
7 nm filter 3nm filter
(d) Estimate of uncontaminated nebulosity (c - b) 2.36 2.15
(e) Ratio of wanted to background (d/b) 0.77 1.72
We see some improvement in the signal to noise ratio, which was the objective. When suitable sky conditions return further analysis will be carried out'
IW 15/11/2023.
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