Astronomik S II 6 nm Filter 36 mm, unmounted

Codice articolo: 8h00n5

The Astronomik [S II] filter is a super-narrow band filter for astro photography. The filter lets only the light of the single ionized sulfur ([S II]) pass.

♦ 97% transmission of the [S II] line

♦ 90 % guaranteed transmission at 672 nm [[S II] line]

♦ 96 % typical transmission at 672 nm [[S II] line]

♦ FWHM 6 nm

♦ Blocks UV and IR completely, necessary for digital photography

♦ Main operational use: planetary nebulae & supernova remnants

♦ Parfocal with other Astronomik filters

♦ No moisture-sensitivity, no aging, and totally scratch-proof

♦ Substrate optically polished

♦ 10 years warranty by manufacturer

♦ Connection: round filter 36 mm, unmounted, protective ring

The Astronomik SII filter is a super-narrow band filter for astro photography from observation sites with light pollution and from dark sites as well.

The filter lets the light of the ionized sulfur [S II] pass, and blocks nearly the whole remainder of the visual spectrum as well as IR, in which the sensor is sensitive.

The contrast between an object glowing at 672 nm and the background is increased enormous!

Due to the combination of the narrow bandwidth of 6 nm and the high transmission of typically 96%, the filter gives you an enormous contrast boost, as all unwanted light is blocked form UV up to the IR. This results in an extremly dark background.

The FWHM of 6 nm is matched to give you optimal performance with CCD and CMOS sensors with a very low dark current! The 6 nm filter is the best choice if you are observing from a heavily light polluted site or if you are imaging faint objects in starcrowded regions of the Milky Way.

Due to the MFR coating technique, you may use one single filter on all instruments up to f/4 without a significant reduction in performance.

Imaging with narrow band emission line filters

If you have to observe from light polluted sites (like most of us ...), imaging with narrow band emission line filters is the best way to take great images, as all kind of light pollution can be blocked very effective! Normaly an H-alpha filter should be your first step into this amazing field of astrophotography! With a narrow band H-alpha filter you will be able to take deep and contrasty images even wih very heavy light pollution or with the full moon high up in the sky! If you look at other astrophotos, an H-alpha is the best choice for all nebulas glowing red! An [O III] filter expands your imaging possibilities, as you are able to image all greenish/blueish structures. Planetary nebulas and star forming regions are great targets! The [S II] filters completes your HSO-set of filters. With these three filters you are able to process your images like the ones from the Hubble space telescope!

The H-beta filter is not available in a 6 nm version, as this filter has nearly no meaningfull application. it is better to use the 6 nm H-alpha filter.

Operation of the filter:

The Astronomik [S II] filter increases the contrast between objects, in this case between the [S II] emission line and the skyglow background. The filter completely suppresses the emission lines of artificial lighting (mercury (Hg) and sodium (Na)) and skyglow. Due to the high optical quality of the Astronomik substrate, you will see the same needle-sharp stars as you would from your regular telescope.

Other uses:

Using the H-alpha and the [O III] filters, you can obtain three-color images of emission line objects (gas nebulae) from locations with very strong light pollution. To do so, you would take an image in three different wavelengths, select each one as a color-channel in Photoshop and paste them together as one single color image.

Alternatives:

The lower priced 12 nm filters are the right choice for you, if you own a typical DSLR or a astro camera with a high dark current! The 12 nm filters should be the fist choice for cameras with an integrated guiding sensor, as you will have about twice as much stars compared to the 6 nm filter.

Note on the protective ring:

Astronomik delivers the round filters from 31 mm diameter with a protective ring at the edge. The corresponding declarations of the manufacturer are available for download as PDF.

Filter transmission curve:




♦ The horizontal axis is the wavelength in nanometers (nm). 500 nm is blue-green, at 600 nm the human eye senses orange and at 650 nm red.
♦ The transmission in % is plotted on the vertical axis.
♦ The red line shows the transmission of the filter.
♦ The [S II] line of single ionized sulfur in nebulae is shown in orange yellow. The square brackets indicate that these lines are forbidden.

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