H-alpha filter passes light at 656nm wavelength. Best choice of narrowband H-alpha astrophotography filter for high-contrast imaging and revealing rich details of the nebula even in areas with strong light pollution,
The 36mm filters fit perfectly into all 36mm filter wheels from ZWO, QHY, QSI, Starlight Xpress, SBIG, Moravian and Atik. The design with a protective ring and blackened filter edges prevents stray light, protects the filters mechanically and makes them easier to handle.
The orientation of the filter in the filter wheel does not matter. It does not change the optical performance.
Photography with narrowband line filters: If you are observing under bright skies, line filters are the best way to get started in astrophotography and take great pictures. An H-alpha filter is usually the first sensible purchase: with this filter, you can easily take detailed pictures even when the moon is full or the sky is very bright! It is also the right filter for all nebulae that glow in red light.
The OIII filter greatly expands your possibilities, as it allows you to capture all greenish/bluish structures in detail and with high contrast. Planetary nebulae and star-forming regions are particularly rewarding targets! With the SII filter, your HSO filter set is complete, and with the three channels you can take colour images like the Hubble Space Telescope!
The H-beta filter is not available in the 6nm version, as this filter has virtually no useful application.
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 lower half-width does 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 6nm filters allow even faint objects to be displayed with high contrast without getting lost in the swarm of stars.
In short, we recommend using 12nm filters for DSLRs and all cameras with limited dark current.
The 6nm 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!
