H-alpha: This filter is suitable for photographing hydrogen nebulae from areas with artificial light pollution, but also from locations with dark skies. The contrasts between objects that glow in H-alpha light and the sky background are greatly enhanced.
Due to the narrow half-width and high transmission of almost 100% in the H-alpha line, the filter achieves a significantly greater contrast increase than broadband filters. The half-width of 12nm is optimally matched to the use of typical CCD and CMOS sensors.
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 tracking stars for almost all cameras with built-in tracking sensors.
The new MFR coating technology makes it possible to use the filter on all instruments up to an aperture ratio of f/3.
Astronomik H-alpha filters are not suitable for solar observation!
The SII filter increases the contrast between SII regions and the sky background. Due to its narrow half-width and high transmission of almost 100% in the SII line, the filter achieves a significantly greater contrast increase than broadband filters. The half-width of 12nm is optimally matched to the use of typical CCD and CMOS sensors.
Even in large cities, images taken with cooled 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.
Narrowband filter for the OIII line at 500.1 nm
This filter is suitable for observation and photography of OIII regions from areas with artificial light pollution or areas with dark skies.
The OIII filter increases the contrast between certain types of astronomical objects (mainly supernova remnants and planetary nebulae) and the sky background. Due to its narrow half-width and high transmission in the OIII line range, it achieves a greater contrast increase than filters with a wider bandwidth. The range of application extends over an aperture ratio of 1:3 to 1:15 for telescopes from 6" (150 mm) aperture for observation at medium magnification and lenses and telescopes of all diameters for astrophotography.
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 two OIII lines can pass through the filter with very high transmission.
Which half-width is the right one? When shooting under dark skies, images taken with a DSLR and even with many cooled CCD cameras are limited by the dark current of the camera and not by the background brightness of the sky. In this case, further suppression of the sky background by a smaller half-width will not reveal any more details in the object! Compared to the 6 nm filters, the 12 nm filters have the advantage that they usually make it easier to find tracking stars with cameras that have a built-in tracking sensor!
If you have a camera with particularly low dark current and good cooling, the 6 nm filters offer all their advantages: Even stronger suppression of sky brightening allows even longer exposure times and thus even deeper images! Due to the low half-width, the stars become tiny, and faint stars disappear almost completely. Especially in Milky Way regions with many stars, the 6 nm filters allow even faint objects to be displayed with high contrast without getting lost in the swarm of stars.
In short, we recommend using 12 nm filters for DSLRs and all cameras with limited dark current.
The 6 nm filters are the right choice in locations with strong light pollution, for cameras with extremely low dark current, and when faint objects require maximum contrast in the image!
