The Altair Astro 3nm ULTRA filters are designed for astro imaging of nebulae with Mono CCD or CMOS cameras, blocking light pollution by cutting out the light pollution wavelengths. The filter blocks UV IR and has an anti-reflection AR coating to suppress halos around bright stars.
Another Altair first - each filter comes with an individual spectrographic report, your guarantee the filter is within tolerance.
A 3nm FHWM gives higher contrast compared to say 6nm FHWM filters, for heavily light-polluted urban areas.
OD4 blocking in visual wavelengths (~0.01%), for ultra high contrast on very faint objects.
AR (Anti Reflection) coatings suppress halo effects and internal reflections for more pleasing star images.
The emission lines of artificial lighting (mercury (Hg) and sodium (Na) as well as skyglow are completely suppressed, allowing for long exposures in urban conditions. LED lighting outside the filter bandpass is also blocked.
Steep transmission curves with narrow pass-bands give high image contrast. Advanced UV/IR blocking coatings give small star sizes even with refractor optics.
These filters perform best from 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 F4.8 or slower optics. An F6 refractor with an 0.8x reducer would give F4.8, and an F7 refractor with 0.8x reducer would give F5.6.
Ultra-flat BK7 glass housed in a precision CNC machined filter cell for strain-free mounting, and freedom from tilt. Filters are 1.85mm thick, 1/4 wave flatness, with 30 arc seconds parallelism. SIO2 tough overcoating for easy cleaning using commercially available optical cleaning products. CWL tolerance is 0.5nm and the measured Transmission at the target wavelength is approximately 90% with a 1% tolerance.