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Broadband Vs Narrowband Images: What's the big deal?

Many images that you see of the night sky are mostly taken through normal phone cameras or even DSLRs. They are what astronomers refer to as "True Colour Images". The reason is simple: all photons that are emitted from space fall onto the camera sensors. What gives these images their colour is via a Baayer matrix that's manufactured together with the camera sensor. However, in deep space, researchers and scientists have discovered that deep space is rich in Hydeogen-Alpha/H-Alpha (Hα) regions.

What is it? H-alpha (Hα) is a specific deep-red visible spectral line with a wavelength of 656.28 nm in air. It occurs when a hydrogen electron falls from its third to second lowest energy level. H-alpha light is the brightest hydrogen line in the visible spectral range. It is important to astronomers as it is emitted by many emission nebulae and can be used to observe features in the Sun's atmosphere, including solar prominences and the chromosphere.

NGC 6188 in H-Alpha

More images of H-Alpha images can be found in my gallery.

That is where narrowband imaging shines: it allows many imagers to capture the specific details of these nebulae while preventing other unwanted wavelengths of light from being captured by the camera sensor. This also means that data can now be captured even with severe light pollution. Of course, it is by no means a magic filter as eventually, light pollution will still slowly creep into your sub-exposures/individual frames should you choose to aim for longer exposures through narrowband filters.

Below is a picture of NGC 3371, a wonderful target in the Southern Hemisphere. Both were taken from the same location with the same sky conditions and telescope. The only difference is that one was taken with a Canon 60D DSLR (Broadband), the other was taken with a dedicated astronomical camera via Narrowband filters (Narrowband)


Canon 60D, Total of 66 mins exposure time (Broadband)

QHY163m, Total of 15 hours of exposure time (Narrowband)

So what's the difference in image 'quality'? Aplenty. In fact, Hubble Images that you see online are mostly constructed via narrowband data taken by the famous Hubble Space Telescope (HST). Since I image from a light polluted city almost 90% of the time, it is only wise that I shoot most of my targets via Narrowband filters.

Disclaimer: this image comparison is not a fair compariosn (It's all I've got at the moment). Within the next few months, I'll be imaging M16, the Eagle nebula with narrowband filters. This is a direct comparison with an image I shot under Bortle 4 skies with a DSLR to present the difference given the better Signal-to-Noise-Ratio (SNR) of the DSLR exposures.

In another blog post, I'll be giving a non biased review with ANTLIA Ultranarrowband filters. Stay tuned!

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