PS: The final images in this article were all taken by Dscad at the Ningxia Habahu Observatory.
It's truly not easy to capture the stunning images when faced with the vast distances and faint light of celestial bodies! To clearly bring out the intricate details and rich colors of nebulae and galaxies, you might just need a few filters.
Astronomical filters play a crucial role in monochrome imaging, helping to create more refined astrophotography images. Combining different filters not only helps reduce the impact of city light pollution but also reveals celestial details and colors. This, in turn, opens up a view for us to explore celestial objects in Hubble false colors.
The light emitted by numerous celestial bodies in the universe spans the entire electromagnetic spectrum. Astrophotographers typically determine which light to block and which to allow through based on the observation target and location.
Astronomical filters selectively transmit certain wavelengths while blocking others. Common filters include LRGB broadband and HSO narrowband filters.
Broadband filters
LRGB filters are essential accessories for monochrome cameras to capture color images, as they enhance contrast in the target area and highlight details. ToupTek Astro 36mm LRGB filters offer a high transmission rate of 95%, covering a wide range of the spectrum. By separately exposing through the RGB channels and later compositing, these filters reveal a color-balanced and natural deep-sky scene.
L filters function as red UV cut-off filters. With a high transmission rate of 98%, they allow visible light between 420 nm and 685 nm to pass through, enhancing contrast in the target area.
R filters allow red light in the range of 590 nm to 700 nm to pass through, while maintaining maximum transmission for H-Alpha and [SII] emissions.
G filters transmit wavelengths between 490nm and 580nm, effectively blocking emission lines from mercury and sodium within this spectral range.
B filters allow transmission within the 400nm to 510nm range, making it more suitable for targets that include the 486nm H-Beta line, such as the Horsehead Nebula.
LRGB final images showcase
Photographer: Dscad
Location: Haba Lake Observatory in Ningxia
Telescope: Airy Disk 106 APO
Main Camera: ToupTek Astro SkyEye62AM
Mount: CEM40
Target: M81 RGB Total Exposure: 2h
Target: Purple Mountain - Atlas comet RGB Total Exposure: 1h
Target: M8 LRGB Total Exposure: 10h
Narrowband filters
Narrowband filters make astrophotography more interesting. Emission nebulae contain rich and complex narrowband emission lines, such as the deep red 656.28 nm Hα emission line, the red [SII] (671.6 nm and 673.1 nm), and the blue-green [OIII] (500.7 nm and 495.9 nm).
Unlike broadband filters, narrowband filters focus on a few very specific wavebands, typically preserving bandwidths of just a few to a dozen nanometers. This precision allows for a more targeted emphasis on the details and characteristics of the observed object within those wavebands.
The latest 36mm HSO filters from ToupTek Astro include an Hα filter centered at a wavelength of 656.3nm with a bandwidth of 3.5nm, as well as [SII] and [OIII] filters, both with a bandwidth of 4nm. The central wavelengths for the [SII] and [OIII] filters are 671.6 nm and 500.7 nm, respectively.
The filters have an Optical Density (OD) value as high as 5.0, effectively blocking other interfering light. An Optical Density (OD) exceeding 5.0 means the filter can reduce transmitted light to less than 1/10^5 of its original intensity. This enhances imaging accuracy and highlights the faint details of deep-sky targets.
In heavily light-polluted environments, the combined use of narrowband filters such as [SII], Hα, and [OIII] can not only mitigate the effects of light pollution and atmospheric scattering but also bring new imaging enjoyment through Hubble Palette.
SHO final images showcase
Photographer: Dscad
Location: Haba Lake Observatory in Ningxia
Telescope: Airy Disk 106 APO
Main Camera: ToupTek Astro SkyEye62AM
Mount: CEM40
Target: NGC2244 SHO Total Exposure: 5h
surface and detail processing
ToupTek Astro LRGB and SHO filters feature a plane optical polish on their surface and are coated with a scratch-resistant layer for repeatable cleaning. To reduce reflections, the edges of the filter are blackened, effectively blocking stray light caused by reflections from the filter's edge. The low scatter design of the surface also helps to block light pollution, minimizing interference from artificial light sources and scattering phenomena.
Products Link
LRGB 36mm Filters: https://www.touptekastro.com/products/lrgb-36mm-filters
SHO 36MM Filters: https://www.touptekastro.com/products/sho-36mm-filters