The Antlia Sulphur-II 2.5nm Ultra narrowband 2" filter has a FWHM (full width half maximum) of an incredible 2.5nm +0.3/-0.1nm and a high transmission efficiency of > 93% at the central wavelength.
These filters are made from quartz glass which has an ultra-low thermal expansion coefficient and outstanding thermal and mechanical properties. Utilizing Antlia's precisely-controlled advanced coating process, these filters are exceptionally durable and can withstand the most challenging environmental conditions, making them ideal for remote observatories.
Compared to the 3nm Pro series, the 2.5nm Ultra filters have a higher transmittance with Ha/SII at ≥95% and OIII at ≥93%. This results in an approximately 20-30% greater signal to noise ratio and excellent contrast. To even further enhance the contrast, and suppress the stray light and internal reflections, Antlia applies edge-blackening coating on each filter.
The maximum transmission of the Hydrogen Alpha and Sulphur-II lines is 95% and Oxygen-III is 93% within 1nm of the centre bandwidth with a flat-top spectral profile, minimizing loss in transmission due to CWL-shift. For best optical performance, the 2.5nm filters are recommended for use with telescopes that have a focal ratio of ≥f/3.5.
Out of band blocking specification is an exceptional OD5 (0.001%), blocking interference from other wavelengths and minimizing halos around bright stars.
Every single filter is individually scanned to ensure a high quality standard, and the included test sheets included in the box are the actual measured spectra and transmission. The tight tolerance of the filters substrate assure a maximum deviance of ±0.05 from specifications, important for parfocality.
The filter cuts off the ultraviolet and infrared light so there is no need to use a UV/IR-cut filter. The quartz glass substrate and improved coatings make these filters more resistant to fractures and scratches.
DO NOT LOOK AT THE SUN WITH THE ANTLIA FILTERS. Serious eye damage will occur.
|2.5 nm +0.3/-0.1 nm (FWHM)
|2.0 mm ±0.05
|1/4 λ (wavefront)
|97% (Ha & SII), 95% (OIII)
|OD5 @ 300-1050 nm
|Double-sided multilayer nano-coating
|60/40 (in accordance with US military watch MIL-O-13830)
|Monolithic optical substrate (non glued)