Narrowband filters increase contrast in emission nebulae by only allowing a specific wavelength range of light to pass through around the spectral lines of hydrogen (H-a, 656 nm), oxygen (OIII, 501 nm), sulphur (SII, 672 nm), etc. The filters can always be used for photography, even when the moon is in the sky, or as filters against light pollution in a large city. The length of the exposure time is irrelevant – even long-exposure photographs can be taken.
The narrow band range of wavelengths is defined as FWHM (full width at half maximum intensity). Narrower band filters reduce background noise. This makes narrow-band filters much more difficult and expensive to manufacture, as attention must be paid not only to the wavelength range but also to the transmission in this small wavelength range. The most difficult part is achieving high transmission for only a very small wavelength range. If, for example, the transmission curve were to drop, the signal for the wavelength range would also drop and the gain for the S/N (signal-to-noise ratio) would no longer be achieved.
This high-quality light pollution filter can be used visually and photographically to increase contrast and allows observations of nebulae, galaxies and star clusters even in light-polluted areas.
The IDAS-NBZ is a new, dual UHC narrow band filter for H-alpha and OIII ranges.
It also counteracts light pollution and considerably increases the contrast within many nebula structures. The NBZ has a very high transmission of 96% and is in no way inferior to other IDAS filters in terms of quality. The filter can be used for observations and photography (DSLR photography) and can even be successfully used on an extremely high-speed RASA or Hyperstar systems with an aperture ratio of up to f/2. This NIR range is blocked up to 1200nm.
As a dual filter, the NBZ allows both oxygen and hydrogen lines pass through. The oxygen range (OIII) is between 495.9nm and 500.7nm here. The hydrogen lines (H-alpha) are allowed through at 656.3nm.
