Astronomik - O III CCD Filter 12 nm - SC thread

The Astronomik [O III] CCD filter is a narrow band emission line filter for CCD photography. The filter lets the light of double ionized oxygen of emission nebulae pass and blocks nearly the whole remainder of the spectrum where the CCD is sensitive. The full width at half maximum (FWHM) of 12 nm is optimal suitable for common CCD cameras and allows the use of very fast optics. The optimal aperture ratio for the use of the filter is 1:3 to 1:15 with apertures of more than 6" (150 mm). It should be noted that the filter has a transmission of up to 99%, which cannot be attained by stacking more narrow-band filters. A further note, which led to selecting the half width (FWHM), is the dark current of common CCD imagers. Exposures with a CCD cooled to -15 °C are limited by the dark current of the CCD, even in large cities with a bright background.

Another advantage of the 12 nm filter is the better availability of guiding stars for cameras with a built-in autoguider (SBIG). If you use a very strong filter like our H-alpha 6 nm filter, you often won’t find a usable guidestar.

Together with our other two Astronomik emission-line CCD filters ([S II] and H-alpha), you can make great color images even from very light polluted places!

Main use:

The Astronomik [O III] CCD filter increases the contrast between objects, in this case between the [O III] emission lines and the skyglow background. This filter 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 bright aperture ratios of 1:2 and more come into play. The filter has a built-in IR-blocker up to 1150 nm. You don’t need an additional IR-blocker with this filter.

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