Manufacturer: Astronomik Filter
Product number: 8h00mh

EUR 129,00


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The Astronomik H-alpha filter is a narrow band filter for astro photography. The filter lets the H-alpha 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 availability of guiding stars for cameras with a built-in-autoguider (SBIG). If you use a very strong filter like the 6 nm filter, you often won’t find a usable guidestar.

An example for an exposure made at the rim a city can be found in "Reviews".

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.

Main use:

The Astronomik H-alpha filter (12 nm version) increases the contrast between objects, in this case H-alpha emitting nebulae, and the skyglow background. This filter completely suppresses the emission lines of artificial lighting (mercury (Hg) and sodium (Na)) and skyglow.

Other uses:
With using the [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.
Achromatic refractors still have chromatic aberrations which make the star images bigger. With lines filters like this one, star images will shrink.
The Astronomik 12 nm H-alpha filter may NOT be used for solar observation.
If you plan to create color images from emission line data, the CLS-CCD filter is a great choice for the Luminance channel.


Suitability:
Visual observation (dark skies): Unsuitable
Visual observation (urban skies): Unsuitable
Film photography: Reasonable, but very long exposure times
CCD and CMOS photography: Very good, huge contrast enhancement at H II-emission nebulae
DSLR photography (original): Good, reduced sensitivity in the H-alpha band
DSLR photography (astro modified): Very good, huge contrast enhancement at H II-emission nebulae
DSLR photography (MC modified): Very good, huge contrast enhancement at H II-emission nebulae
Webcam / Video (Planets): Unsuitable
Webcam / Video (Deep Sky): Good, good contrast enhancement with bright objects


Technical Data:
Transmission of over 97% with the H-alpha line (656 nm)
Complete blocking from all disturbing wavelengths up to infrared
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.


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). 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 see 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.

Transmission at the H-alpha line (656 nm):over 97%
FWHM:12 nm
Carrier material:optically polished substrate
Glass thickness:1 mm
Parfocal:with other Astronomik filters
Anti reflective coating:completely resistant against high humidity, scratches and aging effects
1 filter in plastic box

Image (c) by Wolfgang Ransburg

Location: Munich east
Instrument: William Fluorstar 110 Refractor
Camera: Artemis 4021
Filter: Astronomik H-Alpha 12 nm






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