This filter is suitable for photographing hydrogen nebulae from areas with artificial light pollution, but also from places with dark skies. The contrasts between objects that glow in H-alpha light and the sky background are greatly enhanced.
The H-alpha filter increases the contrast between hydrogen nebulae and the sky background. Due to the narrow half-width and high transmission in the H-alpha line, the filter achieves a greater contrast increase than broadband filters. The half-width of 12nm is optimally matched to the use of common CCD and CMOS sensors. The half-width makes it possible to use fast optics. In addition, the filter has a transmission of almost 100%, which cannot be achieved with narrower filters.
Even in large cities, images taken with cooled CCD cameras are usually limited by dark current. Therefore, further suppression of the sky background by lower half-widths does not reveal more details in the object. Compared to very narrow-band filters, the H-alpha 12nm filter has the advantage that you can usually find guide stars for almost all cameras with built-in tracking sensors. The useful range extends over an aperture ratio of 1:2.8 to 1:15 for lenses and telescopes of all diameters.
Mode of action
The filter completely blocks the emission lines of low- and high-pressure lamps (mercury (Hg) and sodium (Na)) and the lines of the airglow. The filter increases the contrast between objects that glow in the H-alpha emission line and the sky background.
Tips and further usage information
Together with the OIII CCD and SII CCD filters, you can also take three-colour images of emission line objects from locations with very strong light pollution, as is known from images taken by the Hubble Space Telescope, for example. The Astronomik H-alpha filters are not suitable for solar observation!
Suitability of the filter
- Visual observation (country): Not suitable
- Visual observation (city): Not suitable
- Conventional film: Neutral, but very long exposure times
- CCD astrophotography: Very good, extreme contrast gain with H II emission nebulae
- DSLR astrophotography (unmodified): Good, but significantly lower sensitivity in H-alpha than with modified cameras
- DSLR astrophotography (astronomically modified): Very good, extreme contrast gain with H II emission nebulae
- DSLR astrophotography (converted with MC clear glass): Very good, extreme contrast gain with H II emission nebulae
- Webcam / video (Planets): Not suitable
- Webcam / video (deep sky): Good, good contrast gain with bright objects
Technical data for the filter
- Transmission of over 97% at the H-alpha line (656 nm)
- HWB 12 nm
- Complete blocking of all interfering wavelength ranges down to infrared
- Homofocalwith all other Astronomik filters
- Filter thickness: 1 mm
- Not sensitive to moisture, does not age, scratch-resistant
- Fine-optically polished carrier material
- The filter is supplied in a durable case
