Used with a colour astro camera, they help to combat light pollution and make it easier to image deep-sky targets from cities. Compared to mono cameras, one-shot colour cameras also help in this regard as they save time imaging. Combining data captured with a multi-band filter and with a standard light-pollution filter allows some good creativity when it comes to processing; the colour can be changed, and stars moved from one image to another to give some very impressive results.
Here we have examined a selection of multi-band filters to look at the differences in the wavelength of light they let pass through to the camera sensor. There are dual-band filters, which mainly pass the light emission from ionised hydrogen alpha (Ha) and oxygen III (OIII) (though some are now passing sulphur II (SII) and Olll emission), which can enhance the detail within nebulae. There are tri-band filters too, which generally have the addition of passing hydrogen beta emission, useful for adding detail to areas that contain OllI.
The target we chose to image with the eight filters was the Orion Nebula; it has a good mix of gases to image and, in the outer areas beyond the Trapezium, great detail which is harder to capture with standard light-pollution filters. For each multi-band filter, we captured 40x 180-second exposures, processing this with a full set of calibration frames in PixInsight. Further processing was limited to noise control and gentle stretching, but no colour calibration, as we wanted to show what each filter produced.
Optolong L-Ultimate dual-band 3nm filter
2-inch, £389
هذه القصة مأخوذة من طبعة April 2023 من BBC Sky at Night Magazine.
ابدأ النسخة التجريبية المجانية من Magzter GOLD لمدة 7 أيام للوصول إلى آلاف القصص المتميزة المنسقة وأكثر من 8500 مجلة وصحيفة.
بالفعل مشترك ? تسجيل الدخول
هذه القصة مأخوذة من طبعة April 2023 من BBC Sky at Night Magazine.
ابدأ النسخة التجريبية المجانية من Magzter GOLD لمدة 7 أيام للوصول إلى آلاف القصص المتميزة المنسقة وأكثر من 8500 مجلة وصحيفة.
بالفعل مشترك? تسجيل الدخول
Unearthing galaxies in the archives
Comparing old Hubble data to today is revealing distant active galaxies
Voyager 1 is back online and exploring the unknown
An interstellar rescue brings the venerable spacecraft back after months out of action
When Haydn met the Herschels
Jonathan Powell on how the astronomer siblings inspired the famous composer
A quicker way to colourise your narrowband frames
Create a bicolour image in Siril using data from just two narrowband filters
Manhattanhenge
New York's urban island of Manhattan, with its gridiron street layout, sees summer Suns set neatly between skyscrapers. Jamie Carter explains the phenomenon
A very British eclipse
In 1927, Britain experienced its first total solar eclipse since 1724. Mike Frost looks at how, like 8 April 2024's US spectacle, eclipse fever swept the nation
The spirit of the eclipse
Eclipse chaser Yvette Cook reports on what it was like in the path of totality in Texas during 8 April's Great American Eclipse
Cosmic rays
In part two of our series, Govert Schilling looks at cosmic rays, the high-energy particles that bombard Earth from space
Stones of the SOLSTICE
Jamie Carter explores 12 ancient stones, tombs and temples across the world that align with the Sun at the solstice
Surfing spacetime with LISA
A new era of gravitational wave astronomy is on its way as the ambitious upcoming LISA space mission joins a host of huge detectors on Earth. Charlie Hoy explains