Astronomik ASHBCCD50S - H-beta Filter 12 nm, 50 mm, square, unmounted

The Astronomik H-beta filter is a narrow band emission-line filter for astro photography. The filter lets the H-beta light of emission nebulae pass and blocks nearly the whole remainder of the spectrum where the sensor is sensitive.

The full width at half-maximum (FWHM) of 12 nm is optimized for the use with common astro cameras and allows the use of very fast optics. It should be noted that the filter has a transmission of up to 99%. Another advantage of the 12 nm filters is the better availability of guiding stars for cameras with a built-in autoguider (SBIG). If you use a very strong filter like the H-alpha 6 nm filter, you often won’t find a usable guidestar.

Together with two of the other three Astronomik emission-line filters, you can make great color images even from very light polluted places!

The filter has a built-in IR-blocker up to 1150 nm. You don’t need an additional IR-blocker with this filter.

Main use:

The Astronomik H-beta filter increases the contrast between objects, in this case between the H-beta emission line and the skyglow background. This filter completely suppresses the emission lines of artificial lighting (mercury (Hg) and sodium (Na)) and skyglow. The optimal aperture ratio for this filter is 1:3.5 to 1:6. The range of application extends from 1:2.8 to 1:15. 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.

Other uses:

When using the Astronomik H-beta filter together with the H-alpha, [O III] and the [S II] 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 a color image.

When using the Astronomik H-beta filter together with the H-alpha filter, you can create charts of the ionization energy in nebulas by creating an image from the ratio of H-alpha vs. H-beta.

If you plan to create color images from emission line data, the CLS-CCD filter is a great choice for the Luminance channel

The H-beta filter is also great for visual observation. If you plan to get filters for visual observation and for astrophotography, get the photgraphic filter: You may use this filter visual as well as in front of you camera. The built-in IR-blocker doesn’t disturb visual observation, but you need an additional IR-blocker if you want to use the visual filter with your camera.

Suitability:

Visual observation (dark skies): Very good, but only suitable for a few objects

Visual observation (urban skies): Unsuitable

Film photography: It depends, very long exposure time

CCD and CMOS photography: Very good, but only suitable for a few objects

DSLR photography (original): Very good, but only suitable for a few objects

DSLR photography (astro modified): Very good, but only suitable for a few objects

DSLR photography (MC modified): Very good, but only suitable for a few objects

Webcam / Video (Planets): Unsuitable

Webcam / Video (Deep Sky): Unsuitable

Technical Data:

98% transmission at 486 nm (H-beta)

full width at half maximum: 12 nm

complete blocking from 350 nm to 470 nm and 500 nm to 1100 nm

Parfocal with other Astronomik filters

Glass thickness: 1 mm

Completely resistant against high humidity, scratches and aging effects

Diffraction limited, the filter will not reduce the optical performance of your telescope!

Astronomik filters are delivered in a high-quality, long lasting, filter box

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.

Visual filters: The grey line in the background shows the relative sensitivity of the human eye at night. The maximum is at ~510 nm and drops to longer and shorter wavelengths. You can easily see, that you can´t see anything of the H-alpha line at night (even if you can during daylight!) The sensitivity at 656 nm is 0% at night!

Photographic filters: The grey line in the background shows the sensitivity of a typical astro camera sensor.

The most important artifical emission lines are shown in orange. The artifical light pollution is dominated by mercury (Hg) and sodium (Na), which are used in nearly all streetlights.

The most important emission lines from nebulas are shown in green. The most important lines are from ionized hydrogen (H-alpha and H-beta), double ionized oyxgen ([O III]) and ionized sulfur ([S II]). The square brackets indicate that these lines are forbidden.