Astronomik 6 nm H-alpha Filter - 50 mm x 50 mm (square), unmounted

This H-alpha Filter is suitable for imaging of hydrogen nebulas from observation sites with light pollution and from dark sites as well. The contrast between an object glowing at 656 nm and the background is increased enormously!

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 from other wavelengths than 656 nm is blocked from UV up to the IR. This results in an extremely 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 star-crowded 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 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 H-alpha line at 656 nm.

Tips and hints for more applications:

Using the H-alpha filter together with OIII 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:

The lower priced 12 nm filters are the right choice for you if you own a typical DSLR or 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.

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 600 nm red. At 656 nm is the famous "H-Alpha" emission line of hydrogen.

The transmission in % is plotted on the vertical axis.

The red line shows the transmission of the filter.