Altair ColourPRO ULTRA 3nm HSO Narrowband Filter SET 2" CERTIFIED

Product Description

The complete set of 3 Altair 3nm ColourPRO ULTRA narrowband filters at a discounted price.

Another Altair first - each filter comes with an individual spectrographic report, your guarantee the filter is within tolerance.

Altair Astro 3nm ColourPRO ULTRA filters are designed for astro imaging of nebulae with Mono CMOS cameras, blocking light pollution by cutting out the light pollution wavelengths. The filter blocks UV IR and has an anti-halo AR coating to suppress halos around bright stars.

Each filter comes with an individual high resolution spectrographic test 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. You can image in London city centre with these filters and still acquire very good data - in conditions where you cannot even see stars.
New higher blocking of unwanted wavelengths at OD7 ~0.00001% average between 200nm and 1100nm for ultra high contrast on very faint objects. We believe this is the highest blocking factor of any astronomy filter we know of.
Halo suppression with V3R anti reflection coatings. We have not had any reports of halos caused by this filter, and the V3R coatings offer increased transmission of about 2.5% giving an average transmission of 92% across the batch. No filter has less than 90% transmission.
AR (Anti Reflection) coatings suppress halo effects and internal reflections for more pleasing star images and they increase transmission at desired wavelengths.
The emission lines of artificial lighting such as mercury (Hg) and sodium (Na), as well as natural skyglow are completely suppressed, allowing for long exposures in urban conditions. LED lighting outside the filter bandpass is also blocked. Customers have found it's even possibly to image with these filters a couple of hours outside astronomical darkness - within reason of course. Furthermore it's now possible to image at Bortle 9.
Steep transmission curves with narrow pass-bands give high image contrast. Advanced UV/IR blocking coatings give tight star sizes even with refractor optics which show slight bloating in visual wavelengths.
After extensive testing by customers we can confirm these filters perform best from F3.5 or slower optics. Optics faster than F3.5 will still work, but there will be a reduction in contrast and you could get some artefacts. For best performance, we recommend optics slower than F3.5. For example 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 Quartz 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 95% with a 2% tolerance across the batch. No filter has less than 90% transmission.