The Antlia ALP-T 3 nm SII/OIII filter is a narrowband dual-band filter designed for imaging emission nebulae. It transmits the SII line of ionized sulfur at 672.4 nm and the OIII line of doubly ionized oxygen at 500.7 nm. It is primarily designed for color cameras, which can thus capture both of these regions of the spectrum during a single exposure.
CHF 350.06incl. Swiss VAT
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Estimated shipping: Between November 5 and 6, 2026
The Antlia ALP-T 3 nm SII/OIII filter is a narrowband dual-band filter designed for imaging emission nebulae. It transmits the SII line of ionized sulfur at 672.4 nm and the OIII line of doubly ionized oxygen at 500.7 nm. It is primarily designed for color cameras, which can thus capture both of these regions of the spectrum during a single exposure.
Each band has a half-width at half-maximum of 3 nm, with a specified tolerance of ±0.5 nm. The manufacturer’s table lists a peak transmittance of 90 % for SII and 85 % for OIII. Out-of-band rejection reaches at least OD4.5 between 300 and 1100 nm. This combination helps minimize unwanted contributions from light pollution, moonlight, and atmospheric luminescence in nebula images.
Antlia presents this model as a complement to its ALP-T H-alpha/OIII filter. Separate exposures taken with these two filters provide H-alpha, SII, and OIII emissions that can be used to create false-color images. The H-alpha/OIII filter remains a separate product and is not included in this product sheet. The manufacturer also mentions using the SII/OIII filter with a monochrome camera, particularly to simultaneously record both bands in a luminance exposure.
For this standard version, Antlia recommends optics slower than f/4 to achieve optimal performance. For instruments faster than f/4, the manufacturer recommends a version with pre-shifted bands. The model shown here uses a single, non-bonded optical substrate with a thickness of 2 mm ± 0.05 mm. The polishing of both surfaces, the multi-layer coatings, and the anti-reflective coating are designed to minimize internal reflections and halos around stars.
This product is a 2″ filter with an M48 × 0.75 thread. The slim, black-anodized filter holder is designed to preserve the effective aperture and features a laser-engraved design. This photographic filter should not be confused with the HB-OIII model, which is also intended for nighttime observation. Antlia does not recommend visual nighttime observation or solar imaging with the ALP-T SII/OIII. Never look directly at the Sun through this filter, as doing so may cause serious eye damage.
| Strips | SII 672.4 nm; OIII 500.7 nm |
|---|---|
| FWHM | 3 nm ± 0.5 nm per band |
| Peak Transmission | SII: 90 %; OIII: 85 % |
| Blocking | ≥ OD 4.5, 300 to 1,100 nm |
| Thickness | 2 mm ± 0.05 mm |
| Mount | 2″, M48 × 0.75 |
| Recommended Focus Report | Slower than f/4 |
Here are a few accessories we've selected for this model, depending on your needs.
H-alpha/OIII filter set (select 2″ format) for color cameras. Take the images separately and then combine them during processing; check the focal ratio and the alignment.
