Announcement Baader Narrowband F

Astrodon has introduced two new narrowband filter sets with different passbands, 5nm and 3nm. Each set consists of H-alpha, O-III, and S-II narrowband filters. The new transmission curves for these second generation filters are seen below. SBIG is pleased to offer the Astrodon narrowband filters in both 1.25" and 50mm sizes. The 1.25" filters are in threaded cells and fit the CFW9 and CFW10 filter wheels. The 50mm round unmounted filters for the STL series cameras will drop into the standard 5 position internal filter wheel or the optional FW8 eight position filter wheel for the STL cameras.

The narrow range of wavelengths is defined as the FWHM (full-width at half- maximum intensity). Narrower filters decrease the background noise. However, narrower filters are more difficult to manufacture consistently, and are thus more expensive. Furthermore, it is difficult to maintain high transmission through the bandpass of the filter as it becomes narrower. If the peak transmission decreases as the filter is made narrower, the emission signal decreases and the gain in S/N (signal-to-noise) is not realized.

Astrodon has evolved its narrowband product line from 6 nm to 5 nm FWHM, significantly lowered the prices on all filters, and added the ultra-narrow 3 nm FWHM filters for H-a, OIII and SII. A Red Continuum filter has also been added to the line. The Red Continuum filter (645 nm, 5 nm FWHM) produces a star map without the H-a or SII emission in order to subtract stars from emission images.

The 3 nm OIII filter provides the best protection from the effects of moonlight, producing half the background signal of a 90% T, 6 nm FWHM filter, resulting in an increase in S/N of ~21%. Astrodon narrowband filters feature:

28 mm (1.25" threaded cells) for ST series cameras
50.4 mm diameter unmounted for STL cameras
3 mm (+/-0.05) thick
Parfocal to f/4 and parfocal with Astrodon LRGB
H-a, OIII, SII, Red Continuum
5 nm FWHM filters guaranteed >90% transmittance (typically 94-97%)
3 nm FWHM filters typically 90-92% (scan included)
>4 O.D. (out-of-band blocking) 300 - 1150 nm
1/4 wave, striae-free fused silica substrates
30 arcsecond parallelism
sides are blackened
hardest available sputtered coating for durability
3 nm filters can be used on systems to f/3
Designed to have lower blue spectral shift with faster optics