Astronomik 12 nm OIII Filter - 50 mm x 50 mm (square), unmounted

This Astronomik [O III] Filter is suitable for imaging of OIII nebulas from observation sites with light pollution and from dark sites as well. The contrast between an object glowing at 501 nm and the background is increased enormously!

Due to the combination of the narrow bandwidth of 12 nm and the high transmission of typically 96% the filter gives you a contrast boost, as all unwanted light from other wavelengths than 501 nm is blocked (from UV to IR). This results in a very dark background compared with any filters with a higher bandwidth.

The FWHM of 12 nm is optimized for typical DSLR and astro cameras with a normal/high dark current: with these cameras the background signal in images taken from heavily light-polluted sites is dominated by the dark current of the sensor, not by flux coming from light pollution. In this case a further reduction of FWHM does not improve the image, as the background will not get darker. Compared to the 6 nm filters you have more stars in the field of view which gives you more guiding stars when working with an integrated/dual guiding chip!

Due to the new MFR coating technique you may use one single filter on all instruments up to f/3 without a significant reduction in performance.

Imaging with narrowband emission line filters:

If you have to observe from light polluted sites (like most of us ...), imaging with narrowband emission line filters is the best way to take great images, as all kind of light pollution can be blocked very effective! Normally an H-alpha filter should be your first step into this amazing field of astrophotography! With a arrowband H-alpha filter you will be able to take deep and contrasty images even with very heavy light pollution or with the full moon high up in the sky!

If you look at other astrophotos, an H-alpha filter is the best choice for all nebulas glowing red! An OIII filters expands your imaging possibilities, as you are able to image all greenish/blueish structures. Planetary nebulas and star forming regions are great targets! The SII filter 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.

Operation of the filter:

The filter blocks all unwanted light from artifical light pollution, natural airglow and moonlight. Especially light from high and low pressure sodium and mercury lights and all lines of natural airglow are 100% blocked. The filter increases the contrast between the sky background and objects glowing at the [O III] line at 501 nm.

Tips and hints for more applications:

Using the OIII filter together with H-alpha and SII filters, you can produce false color emission line images (HSO) in the same way as the Hubble Space Telescope. This is possible even from heavily light-polluted sites

Alternatives:

If want to image faint objects in star-crowded regions of the milky way, propably using short focal lengths, the 6 nm filter will be the better choice, as the number of stars is reduced by a factor of ~2. You should even take the 6 nm version if you have a camera with a low thermal current or if you have to observe from a really heavily light-polluted site.

Filter transmission curve:

The horizontal axis is the wavelength in nanometers (nm). 400 nm is deep blue, at 520 nm the human eye senses green and at 630 nm bright red. At 656 nm is the famous "H-Alpha" emission line of hydrogen.

The transmission in % is plotted on the vertical axis.

The green line shows the transmission of the filter.