Product no.: 16454Manufacturer: Astrodon
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Narrow-band filters achieve a contrast enhancement in emission nebulae, except that they can only nominate a member of the wavelength range of light to the spectral lines of hydrogen (Ha, 656nm), oxygen (OIII, 501 nm), sulfur (SII, 672nm), and so throughout. The filter can always be used for photography, even when the moon is in the sky, or as a filter against the light pollution in a major city. Here, the length of exposure time does not matter - can also be made long-term photography. The narrow-band range of wavelengths than FWHM (English full-width at half-maximum intensity) is defined. Narrow-band filters reduce background noise. Therefore narrowband filters in the production are much more difficult and more expensive, because here are respected not only on the wave length range, but also to the passage in this small wavelength range needs. The hardest part is to achieve a high transmittance for only a very small wavelength range. If for example, would decrease the transmission curve, the signal would drop for the wavelength range and the gain for the S / N (signal to noise ratio) would no longer be achieved.
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