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Astronomik H-Alpha 6nm CCD Filter 1.25" (E28.5)


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Astronomik H-Alpha 6nm CCD Filter 1.25" (E28.5)
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Astronomik H-Alpha 6nm CCD Filter 1.25" (E28.5)

The Astronomik 6nm H-alpha filter is an extremely narrow emission-line filter for CCD photography. The filter lets the H-alpha light of emission nebulae pass and blocks nearly the whole remainder of the spectrum where your CMOS/CCD camera is sensitive.

The full width at half-maximum (FWHM) of 6nm is optimized for a maximum contrast between the (H-alpha emitting) object and the background. The contrast gain is much higher than with our 12nm emission line filters but you won’t see as many stars in the resulting images. The design of the transmission curve makes it possible to use the filters with instruments from f/3.75 to f/15. Selected filters for faster system are available upon special request.

Main use

The Astronomik H-alpha-CCD (6nm version) increases the contrast between objects, in this case between the H-alpha emission line and the skyglow background in the same way as the 12nm version. The gain in contrast is much higher due to the smaller FWHM. The 6nm H-Alpha filter is the right choice for extremely dim objects, even in the Milky Way, and for imaging from heavily light-polluted places. The Astronomik 6nm H-alpha-CCD completely suppresses the emission lines of artificial lighting (mercury (Hg) and sodium (Na)) and skyglow. Transmission losses and chromatic distortions, which arise with other filters, only occur with Astronomik filters when extremely fast focal ratios come into play. Selected filters for faster systems are available upon special request.

Other uses

  • Using the Astronomik 6nm H-Alpha together with the 12nm H-Alpha gives you the ability to have a maximum contrast in the HII objects and to keep the maximum amount of stars in the final image.

  • The Astronomik 6nm H-Alpha filter may NOT be used for solar observation.


If you plan to do (false-)color imaging with other emission line filters, you should get our filters with 12nm FWHM. Images taken with filters with differing FWHM are very difficult to combine into the final image.

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