Altair Astro ULTRA 3 nm filters are designed for astronomical imaging of nebulae with Mono CCD or CMOS cameras, and block light pollution by removing wavelengths of light pollution. The filter blocks ultraviolet and infrared rays and has an AR anti-halo coating to prevent halos around bright stars.
Another new feature from Altair: each filter comes with an individual spectrographic report, ensuring that the filter is within tolerance.
- A 3 nm FHWM filter provides higher contrast compared to e.g. 6 nm FHWM filters for urban areas with high light pollution.
- OD4 blocking at visual wavelengths (~0.01%), for ultra-high contrast on very faint objects.
- No halos. We have received no reports of halos caused by this filter.
- AR (anti-reflection) coatings suppress halo effects and internal reflections for more pleasing star images.
- Artificial illumination emission lines (mercury (Hg) and sodium (Na), as well as sky glow, are completely suppressed, allowing long exposures in urban conditions. LED illumination outside the filter bandpass is also blocked.
- Steep transmission curves with narrow pass bands provide high image contrast. Advanced UV and IR blocking coatings provide small star sizes even with refractive optics.
These filters work best with F4.8 or slower optics. Optics faster than F4.8 will still work, but there will be a reduction in contrast. For best performance, we recommend an F4.8 or slower optic. An F6 refractor with a 0.8x reducer would give F4.8, and an F7 refractor with a 0.8x reducer would give F5.6.
Ultra-thin BK7 glass housed in a precision CNC-machined filter cell for stress-free, tilt-free mounting. Filters are 1.85mm thick, 1/4 wave flatness and 30 arc second parallelism. Tough SIO2 coating for easy cleaning with commercially available optical cleaners. CWL tolerance is 0.5 nm and measured transmission at the target wavelength is approximately 90% with a 1% tolerance.
