The Antlia SHO Ultra 2.5 nm set combines the H-alpha, SII, and OIII filters from the Ultra series. It allows you to capture the main emissions from nebulae in these three spectral bands separately. Each option listed here corresponds to the complete set of three filters in the same format—either 2″ mounted or 36 mm unmounted.
Price range: CHF 1'196.91 through CHF 1'518.66
The Antlia SHO Ultra 2.5 nm set combines the H-alpha, SII, and OIII filters from the Ultra series. It allows you to capture the main emissions from nebulae in these three spectral bands separately. Each option listed here corresponds to the complete set of three filters in the same format—either 2″ mounted or 36 mm unmounted.
The Ultra series has a half-width at half-maximum of 2.5 nm, with a tolerance of +0.3/−0.1 nm. The manufacturer specifies a transmission of at least 95 % at 656.3 nm for H-alpha and at the 671.6 and 673.1 nm lines for SII. For OIII, the specified transmission is at least 92 % at 500.7 nm. The flat-top spectral profile is designed to minimize transmission loss caused by the centerband shift within the optical beam.
Ultra filters are manufactured on a quartz substrate, whose low coefficient of thermal expansion contributes to the component’s stability. Antlia combines this glass with fine polishing on both sides and a controlled optical coating process. Out-of-band rejection is specified at a minimum of OD5. The design is intended to reduce spurious signals outside the useful bands as well as halos around bright stars.
The 2″ version uses slim, black-anodized M48 × 0.75 threaded mounts. The 36 mm option consists of unmounted discs with blackened edges; it requires a housing designed for these filters. The nominal thickness is 2 mm for both sizes. Antlia recommends a focal ratio of f/3.5 or greater to achieve the best optical performance from the Ultra 2.5 nm series. This recommendation should be taken into account before selecting this set for a fast instrument.
Antlia states that each filter is individually measured and that the transmission and block curves provided in the box correspond to actual measurements. The attention to detail regarding thickness and polishing ensures good parfocality among the filters. This package differs from the SHO Pro 3 nm kit and the three Ultra filters sold individually: it includes H-alpha, SII, and OIII. Antlia does not recommend using these filters for solar imaging or nighttime visual observation. Never use these filters to view the Sun.
| Contents | Three filters: H-alpha, SII, and OIII |
|---|---|
| FWHM | 2.5 nm, +0.3/−0.1 nm |
| Substrate | Quartz |
| Transmission | H-alpha and SII ≥ 95 %; OIII ≥ 92 % |
| Blocking | ≥ OD5 |
| Nominal thickness | 2 mm |
| Recommended Focus Report | ≥ f/3.5 |
| Formats | 2″ mounted or 36 mm unmounted |
